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CHAMPAGNE, C. P., F. GIRARD, and N. MORIN. "Inhibition of the Psychrotrophic Bacteria of Raw Milk by Addition of Lactic Acid Bacteria." Journal of Food Protection 53, no. 5 (May 1, 1990): 400–403. http://dx.doi.org/10.4315/0362-028x-53.5.400.
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Two commercial cultures of lactic acid bacteria (LAB) were added to raw milk in order to inhibit the development of psychrotrophic bacteria. The effects of inoculation level, pH development, media for culture preparation, and milk heat treatment on the inhibitory activity of LAB were studied. Inoculation levels of 2.5 × 106/mL and less of LAB did not significantly reduce psychrotrophic growth. Maximum inoculation level of LAB studied was 25 × 106/mL and this reduced psychrotrophic development by a factor of 10; however, milk pH was reduced to 6.54 over 48 h of incubation at 7°C with this inoculation level. This acidification was not responsible for the inhibitory activity of LAB on psychrotrophs. The LAB were more effective when psychrotroph populations had high multiplication rates. Initial populations of Pseudomonas putida in pasteurized milk did not influence the activity of the LAB. Pseudomonas putida grew faster in sterile milk than in pasteurized milk, but average inhibition rates of LAB were similar in both media.
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Ahmed, S., S. MMR Sumon, MD Hossain, ABM Rubayet Bostami, and MM Rahman. "Prevalence of Psychrotrophic Bacteria During Frozen Storage of Raw Milk." Annals of Bangladesh Agriculture 24, no. 1 (February 8, 2021): 65–76. http://dx.doi.org/10.3329/aba.v24i1.51936.
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The study was aimed to enumerate the load of psychrotrophic bacteria in raw milk stored in freezer. Raw milk was collected from 18 different sized dairy farms located in Gazipur and Mymensingh district. From each location equal number (three of each) of small, medium or large farms were randomly selected. The raw milk samples were stored in freezer (-18 to -22 oC) for 28 days and analyzed for psychrotrophic bacterial load at every 7 days interval. For total viable count, bacteria was grown onto plate count agar at 70C for 10 days. Bacteria grown under such conditions referred as psychrotrophs. However, to determine the type of psychrotrophs selected colonies were grown further onto pseudomonas agar base and gram staining, oxidase, catalase and methyl red test for each isolate were perfomed. The psychrotrophic bacterial load in all the samples were low until 14 days of storage. However, from the third week of storage the bacterial load was observed to increase which reached to as high as 1.1 ± 2.3×107 cfu/mL at the end of the storage period (28 days). The milk samples obtained from large farms were lower (1.3×105 to 6.6×106) than that of medium (1.7×105 to 8.8×106) and small (2.0×105 to 1.1×107) type farms. The bacterial load was significantly (P<0.01) varied among the samples suggesting the heterogeneous management practices in dairy farms. All the morphological and biochemical tests confirmed the isolates as pseudomonas. Based on the present findings, it could be suggested that raw milk can store in the freezer maximum for two weeks in terms of psychrotrophic bacterial load.
Ann. Bangladesh Agric. (2020) 24(1) : 65-76
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Malimon, Z., M. Kukhtyn, N. Grynevych, and N. Mekh. "Analysis of the insemination of the mesophilic and psychrotrophic microflora of frozen fish." Naukovij vìsnik veterinarnoï medicini, no. 1(149) (May 30, 2019): 22–29. http://dx.doi.org/10.33245/2310-4902-2019-149-1-22-29.
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The article presents the results of research on the dehiscence of frozen fish with mesophilic and psychrotrophic microflora. Physico-chemical and organoleptic changes which appear in fish during refrigeration are connected with the life of the psychotropic group of microflora, which is more active than mesophilic. Fish are a nutrient medium for the development of microorganisms of all groups, due to its high nutritional and biological value, so the fish are perishable food products, the conditions and terms of their storage require appropriate temperature regimes to stop the development of microorganisms. The aim of the work was carrying out a comparative analysis of insemination of frozen fish with mesophilic and psychrotrophic microflora to make an amend to standards according to microbiological criteria. The microbial number in frozen fish samples was estimated with the temperature of (30 ± 1) ºC incubation of crops for 72 hours (mesophilic microflora) and incubation for 10 days (psychrotrophic microflora) with the temperature (6.5 ± 0.5) ºC. It was identified that there were taken the samples from frozen fish with a quantity of mesophilic bacteria to 102 CFU/g, 1.4-1.8 times (p <0.05) more psychotropic microorganisms. The researched samples with the number of mesophilic microorganisms from 103 to 104 CFU/g were contaminated with psychotropic microflora, which in 1.7-6.8 times (p <0.05) exceeded the content of the mesophilic microflora. With such amount of mesophilic microorganisms, on average of up to 25% of samples, this had a content of psychotrophs of more than 105 CFU/g of fish. According to the content of mesophilic bacteria the samples of frozen fish, which were mathed to a certain norm of 5 × 104 CFU/g, basically in the number of psychrotrophic microflora did not correspond to this indicator, and exceeded it 2 times or more. In the cold period of the year, 63.6 ± 2.1% of frozen fish samples were mesophilic bacteria containing less than 101 CFU/g. At the same time, samples with such content mesophilic bacteria in the warm period of the year was 9.0%, or 7.0 times (p <0.05) less. In addition, in the cold period of the year, only 9.0% of samples were detected, which, according to the content of mesophilic bacteria exceeded the maximum allowable level. At the same time, during the warm period, the number of samples with an excess of mesophilic bacteria content was 27.3 ± 0.3%. Practically the same pattern was observed regarding the insemination of the psychrotrophic microflora in these periods of the year, which was characterized by the fact that in the warm period of the year, frozen fish contains a large number of psychrotrophic microorganisms. Consequently, the results of studies on the amount of microflora in the warm period of the year established 3,0 times (p <0,05) more samples of frozen fish, which, according to the content of mesophilic bacteria, exceeded the maximum permissible level compared with the cold period of the year. It was established that samples of frozen fish containing mesophilic microorganisms less than 101 CFU/g were most unevenly contaminated with psychrotrophic microflora. Among these samples, only 30.1 ± 1.4% were with the number of psychrotrophic microflora less than 101 CFU/g, at the same time, 60.0 ± 0.5% of the samples were contaminated with a psychrotrophic microflora of 101 to 105 CFU/g and 10, 0 ± 0.2% over 105 CFU/g. In the study of frozen fish samples with the number of mesophilic bacteria from 101 to 102 CFU/g revealed a coincidence in the content of psychrotrophs in only 16,7 ± 0,3% of samples, and 33,3 ± 0,3% of fish samples were with the content of psychrotrophic microflora from 102 to 103 CFU/g and 103 to 104 CFU/g and 16.7 ± 0.3% were contaminated with psychrotrophy more than 104 CFU/g. It was established that samples of frozen fish containing mesophilic microorganisms less than 101 CFU/g were most unevenly contaminated with psychrotrophic microflora. Among these samples, only 30.1 ± 1.4% were with the number of psychrotrophic microflora less than 101 CFU/g, at the same time, 60.0 ± 0.5% of the samples were contaminated with a psychrotrophic microflora of 101 to 105 CFU/g and 10, 0 ± 0.2% over 105 CFU/g. In the study of frozen fish samples with the number of mesophilic bacteria from 101 to 102 CFU/g revealed a coincidence in the content of psychrotrophs in only 16,7 ± 0,3% of samples, and 33,3 ± 0,3% of fish samples were with the content of psychrotrophic microflora from 102 to 103 CFU/g and 103 to 104 CFU/g and 16.7 ± 0.3% were contaminated with psychrotrophy more than 104 CFU/g. It was found that that the psychrotrophic microflora of frozen fish is quantitatively predominantly content of mesophilic bacteria several orders of magnitude. During the warm period of the year, more samples of frozen fish were detected in 3,0 times (p <0,05), which, according to the content of mesophilic bacteria, exceeded the maximum permissible level in comparison in the cold period of the year. It was found that 92,6 ± 2,5% of frozen fish samples were in compliance with the requirements of DSTU 4868: 2007. The fish is frozen. At the same time, during the fish evaluation, the contents of the psychrotrophic microflora showed that samples exceeding 5 × 104 CFU/g was in 2.6 times (p <0.05) more than the mesophilic bacteria content. In future the generic and species composition of the psychrotrophic microflora of frozen fish will be studied and the fish evaluating criteria according to the psychrotrophs in order to make corrections according to the microbiological criteria. Key words: frozen fish, psychrotrophic microflora, mesophilic bacteria, contamination, microbial number.
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Munsch-Alatossava, Patricia, Jean-Pierre Gauchi, Bhawani Chamlagain, and Tapani Alatossava. "Trends of Antibiotic Resistance in Mesophilic and Psychrotrophic Bacterial Populations during Cold Storage of Raw Milk." ISRN Microbiology 2012 (March 12, 2012): 1–13. http://dx.doi.org/10.5402/2012/918208.
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Psychrotrophic bacteria in raw milk are most well known for their spoilage potential and cause significant economic losses in the dairy industry. Despite their ability to produce several exoenzyme types at low temperatures, psychrotrophs that dominate the microflora at the time of spoilage are generally considered benign bacteria. It was recently reported that raw milk-spoiling Gram-negative-psychrotrophs frequently carried antibiotic resistance (AR) features. The present study evaluated AR to four antibiotics (ABs) (gentamicin, ceftazidime, levofloxacin, and trimethoprim-sulfamethoxazole) in mesophilic and psychrotrophic bacterial populations recovered from 18 raw milk samples, after four days storage at C or C. Robust analysis of variance and non parametric statistics (e.g., REGW and NPS) revealed that AR prevalence among psychrotrophs, for milk samples stored at C, often equalled the initial levels and equalled or increased during the cold storage at C, depending on the AB. The study performed at C with an intermediate sampling point at day 2 suggested that (1) different psychrotrophic communities with varying AR levels dominate over time and (2) that AR (determined from relative amounts) was most prevalent, transiently, after 2-day storage in psychrotrophic or mesophilic populations, most importantly at a stage where total counts were below or around CFU/mL, at levels at which the milk is acceptable for industrial dairy industrial processes.
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Shtenikov, M. D., O. Y. Zinchenko, and V. V. Boldyreva. "ANTAGONISTIC ACTIVITY OF MARINE BACTERIA OF BACILLUS, PRIESTIA AND PAENIBACILLUS GENERA OF DIFFERENT THERMOTYPES." Microbiology&Biotechnology, no. 2(55) (September 20, 2022): 50–65. http://dx.doi.org/10.18524/2307-4663.2022.2(55).261778.
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SummaryAim. To study the antagonistic activity of bacteria of genera Bacillus, Priestia and Paenibacillus at different conditions of cultivation. Methods. Antagonistically active spore-forming bacteria isolated from deep-sea bottom sediments of the Black Sea were used for the study. Determination of thermotypes was performed using the results of analysis of fatty acid profile parameters. Antagonistic activity to test strains of bacterial opportunistic pathogens was detected by the method of agar blocks on Gauze № 1 and Nutrient Agar media at different cultivation temperatures. Results. Aerobic bacilli of genera Bacillus, Priestia and Paenibacillus of all three thermotypes – thermotolerants, mesophiles and psychrotrophes, in general show lower antagonistic activity when cultured at 37 °C on both media, except for a marked increase in psychrotrophe antagonistic activity at 37 °С on Gauze № 1. Conclusions. It was established that belonging to a certain thermotype affects the character of the antagonistic activity of sporeforming bacteria. The antagonistic activity of mesophilic and thermotolerant bacteria at a higher temperature of cultivation is lower, and that of psychrotrophic bacteria at a higher temperature and on Gauze № 1 medium is higher.
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Verhegghe, M., J. De Block, S. Van Weyenberg, L. Herman, M. Heyndrickx, and E. Van Coillie. "Effect of a pre-milking teat foam and a liner disinfectant on the presence of mesophilic and (proteolytic) psychrotrophic bacteria prior to milking." Journal of Dairy Research 86, no. 4 (November 2019): 432–35. http://dx.doi.org/10.1017/s0022029919000700.
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AbstractContamination of raw milk by psychrotrophs can lead to the production of heat-resistant proteases and subsequent spoilage of UHT milk. Therefore, this research communication evaluated the effect of a pre-milking teat disinfectant (active components: L-(+)-lactic acid and salicylic acid) and a liner disinfectant (active components: peracetic acid and hydrogen peroxide) on the number of mesophilic and (proteolytic) psychrotrophic bacteria prior to milking. The teat orifices of 10 cows were sampled using a swabbing procedure before and after treatment with a pre-milking teat disinfectant on six subsequent days. On the teat orifices, there was a small but statistically significant decrease in the psychrotrophic bacterial counts between pre and post dipping. No differences were observed for the mesophilic bacterial counts and proteolytic active counts. Liners were also sampled using swabs pre and post disinfection. No statistically significant decrease in the bacterial counts was observed post liner disinfection, although there was a numerical decrease. Sixty-two percent of the proteolytic psychrotrophs were pseudomonads: 16.5% of which were P. fragi, 14.3% P. lundensis, 10.0% P. fluorescens and 2.9% P. putida. Trinitrobenzenesulfonic acid (TNBS) analysis revealed a wide variety in proteolytic activity (from 0 to 55 µmol glycine/ml milk) and the presence of high producers. It can be concluded that there was only a minor effect of teat and liner disinfection on the psychrotrophic bacterial counts indicating that the measures presented did not result in a reduction of the targeted bacteria on teat orifices and liners.
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Przemieniecki, Sebastian Wojciech, Tomasz Paweł Kurowski, Karol Korzekwa, and Anna Karwowska. "The effect of psychrotrophic bacteria isolated from the root zone of winter wheat on selected biotic and abiotic factors." Journal of Plant Protection Research 54, no. 4 (December 30, 2014): 407–13. http://dx.doi.org/10.2478/jppr-2014-0061.
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Abstract The roots of winter wheat plants, cv. Mikon, grown in 45-year monoculture, were analysed in the study. Twenty-two bacterial isolates obtained from the rhizosphere, rhizoplane, and endorhizosphere that were capable of growth at 8°C and at 28°C, were selected for further analysis. The isolated psychrotrophs accounted for 25% of all bacteria present in the wheat rhizosphere and capable of growth at 8°C. Psychrotrophic bacteria were analysed at a temperature of 10°C and 28°C to determine their ability to inhibit the growth of pathogenic fungi, solubilise mineral phosphates, and to determine their ability to degrade chitin and cellulose. Similarity between the isolates was determined by Enterobacterial Repetitive Intergenic Consensus – Polymerase Chain Reaction (ERIC-PCR) and Random Amplification of Polymorphic DNA – Polymerase Chain Reaction (RAPD-PCR). The majority of isolated psychrotrophs inhibited the growth of pathogenic fungi and solubilised mineral phosphates at both incubation temperatures. Psychrotrophic bacteria exerted a two-fold stronger inhibitory effect on mycelial growth at 10°C than at 28°C. The growth of Fusarium culmorum and F. oxysporum was inhibited to the highest extent at 10°C and at 28°C, respectively. Phosphate solubilisation rates were higher at 28°C, particularly in the rhizosphere. Regardless of temperature, the bacteria exhibited low chitin-degrading potential, and none of the isolates was capable of degrading cellulose. A high similarity between the selected psychrotrophs was revealed by ERIC-PCR and RAPD- -PCR analyses. Based on RAPD-PCR, the analysed population was divided into a group of isolates obtained from the rhizosphere, and two groups comprising representatives of both the rhizoplane and the endorhizosphere. Due to their ability to grow over a wide temperature range and increase phosphorus availability to plants, and their antagonism against pathogens, psychrotrophic bacteria can be used to improve the growth and yield of cereal crops.
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Teider Junior, Pedro I., José C. Ribeiro Júnior, Eric H. Ossugui, Ronaldo Tamanini, Juliane Ribeiro, Gislaine A. Santos, Amauri A. Alfieri, and Vanerli Beloti. "Pseudomonas spp. and other psychrotrophic microorganisms in inspected and non-inspected Brazilian Minas Frescal cheese: proteolytic, lipolytic and AprX production potential." Pesquisa Veterinária Brasileira 39, no. 10 (October 2019): 807–15. http://dx.doi.org/10.1590/1678-5150-pvb-6037.
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ABSTRACT: The most consumed cheese in Brazil, Minas Frescal cheese (MFC) is highly susceptible to microbial contamination and clandestine production and commercialization can pose a risk to consumer health. The storage of this fresh product under refrigeration, although more appropriate, may favor the growth of spoilage psychrotrophic bacteria. The objective of this study was to quantify and compare Pseudomonas spp. and other psychrotrophic bacteria in inspected and non-inspected MFC samples, evaluate their lipolytic and proteolytic activities and their metalloprotease production potentials. Twenty MFC samples were evaluated: 10 inspected and 10 non-inspected. Counts of psychrotrophic bacteria and Pseudomonas spp., evaluation of the proteolytic and lipolytic potential of the isolates, and identification of potential producers of alkaline metalloprotease (AprX) were assessed. The mean total psychrotrophic counts were 1.07 (±2.18) × 109CFU/g in the inspected samples and 4.5 (±5.86) × 108CFU/g in the non-inspected, with no significant difference (p=0.37). The average score of Pseudomonas spp. was 6.86 (±18.6) × 105 and 2.08 (±3.65) × 106 CFU/g for the inspected and non-inspected MFC samples, respectively, with no significant difference (p=0.1). Pseudomonas spp. represented 0.06% and 0.004% of psychrotrophic bacteria found in inspected and non-inspected MFC samples, respectively. Collectively, 694 psychrotrophic strains and 47Pseudomonas spp. were isolated, of which 59.9% and 68.1% were simultaneously proteolytic and lipolytic, respectively. Of the 470 psychrotrophs isolated from inspected and 224 from non-inspected cheese samples, 5.74% and 2.23% contained aprX, respectively, while 100 and 86.96% of the Pseudomonas spp. isolates in inspected and non-inspected cheese samples contained the gene. The production potential of AprX did not, however, determine the proteolytic activity on plates of these isolates under the conditions evaluated in this study. Of total, 65.63% of the psychrotrophs that contained aprX gene were confirmed as Pseudomonas spp., using genus-specific PCR. Phylogenetic analysis of the 16S rRNA gene of the other psychrotrophs that were potential producers of AprX identified them as Serratia spp. (n=7), Raoultella ornithinolytica (n=1), and Acinetobacter schindleri (n=1) in the inspected samples and Psychrobacter sanguinis (n=1) and Leuconostoc mesenteroides (n=1) in the non-inspected samples. The production conditions of Brazilian MFC of these samples, while meeting the legal determinations, are not sufficient to control Pseudomonas and other spoilage-related psychrotrophs. Thus, stricter hygienic measures are required during the formal production of this type of cheese.
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Hantsis-Zacharov, Elionora, and Malka Halpern. "Culturable Psychrotrophic Bacterial Communities in Raw Milk and Their Proteolytic and Lipolytic Traits." Applied and Environmental Microbiology 73, no. 22 (September 21, 2007): 7162–68. http://dx.doi.org/10.1128/aem.00866-07.
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ABSTRACT During cold storage after milk collection, psychrotrophic bacterial populations dominate the microflora, and their extracellular enzymes, mainly proteases and lipases, contribute to the spoilage of dairy products. The diversity, dynamics, and enzymatic traits of culturable psychrotrophs in raw milk from four farms were investigated over a 10-month period. About 20% of the isolates were found to be novel species, indicating that there is still much to be learned about culturable psychrotrophs in raw milk. The psychrotrophic isolates were identified and classified in seven classes. Three classes were predominant, with high species richness (18 to 21 species per class) in different seasons of the year: Gammaproteobacteria in spring and winter, Bacilli in summer, and Actinobacteria in autumn. The four minor classes were Alphaproteobacteria, Betaproteobacteria, Flavobacteria, and Sphingobacteria. The dominant classes were found in all four dairies, although every dairy had its own unique “bacterial profile.” Most but not all bacterial isolates had either lipolytic or both lipolytic and proteolytic activities. Only a few isolates showed proteolytic activity alone. The dominant genera, Pseudomonas and Acinetobacter (Gammaproteobacteria), showed mainly lipolytic activity, Microbacterium (Actinobacteria) was highly lipolytic and proteolytic, and the lactic acid bacteria (Lactococcus and Leuconostoc) displayed very minor enzymatic ability. Hence, the composition of psychrotrophic bacterial flora in raw milk has an important role in the determination of milk quality. Monitoring the dominant psychrotrophic species responsible for the production of heat-stable proteolytic and lipolytic enzymes offers a sensitive and efficient tool for maintaining better milk quality in the milk industry.
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Whyte, Lyle G., Charles W. Greer, and William E. Inniss. "Assessment of the biodegradation potential of psychrotrophic microorganisms." Canadian Journal of Microbiology 42, no. 2 (February 1, 1996): 99–106. http://dx.doi.org/10.1139/m96-016.
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Bioremediation of polluted temperate and cold temperature environments may require the activity of psychrotrophic bacteria, because their low temperature growth range parallels the ambient temperatures encountered in these environments. In the present study, 135 psychrotrophic microorganisms isolated from a variety of ecosystems in Canada were examined for their ability to mineralize14C-labelled toluene, naphthalene, dodecane, hexadecane, 2-chlorobiphenyl, and pentachlorophenol. A number of the psychrotrophic strains mineralized toluene, naphthalene, dodecane, and hexadecane. None of the psychrotrophs were capable of mineralizing 2-chlorobiphenyl or pentachlorophenol. Those strains demonstrating mineralization activity were subsequently screened by the polymerase chain reaction (PCR) and Southern hybridization of PCR products for the presence of catabolic genes (alkB, ndoB, todC1, and xylE) involved in known bacterial biodegradative pathways for these compounds. Some of the psychrotrophs able to mineralize toluene and naphthalene possessed catabolic genes that hybridized to xylE or todC1, and ndoB, respectively. The alkB PCR fragments obtained from the strains that mineralized dodecane and hexadecane did not hybridize to an alkB gene probe derived from Pseudomonas oleovorans. Psychrotrophic strain Q15, identified as a Rhodococcus sp., also mineralized the C28n-paraffin octacosane. A gene probe constructed from the "alkB" PCR fragment from strain Q15 did hybridize with the alkB PCR fragments from most of the psychrotrophic alkane biodegraders, indicating that the alkB primers may be amplifying another gene(s), perhaps with low homology to P. oleovorans alkB, which may be involved in the biodegradation of both short chain (dodecane) and longer chain alkanes (hexadecane, octacosane). All of the psychrotrophic biodegradative isolates examined were capable of mineralization activity at both 23 and 5 °C, indicating their potential for low temperature bioremediation of petroleum hydrocarbon contaminated sites.Key words: psychrotrophic microorganisms, biodegradation, catabolic gene probes, organic pollutants.
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Khalafalla, F., and A. El-Sherif. "Psychrotrophic bacteria in sausage." Food / Nahrung 37, no. 5 (1993): 428–32. http://dx.doi.org/10.1002/food.19930370504.
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YUAN, LEI, FAIZAN A. SADIQ, METTE BURMØLLE, NI WANG, and GUOQING HE. "Insights into Psychrotrophic Bacteria in Raw Milk: A Review." Journal of Food Protection 82, no. 7 (June 21, 2019): 1148–59. http://dx.doi.org/10.4315/0362-028x.jfp-19-032.
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ABSTRACT Supply of high-quality dairy products is the goal of every dairy producer throughout the world. However, psychrotrophic bacteria in raw milk, generally comprising bacterial species of the genera Pseudomonas, Acinetobacter, Aeromonas, Serratia, Bacillus, Lactococcus, Microbacterium, and Staphylococcus, are of special concern to the dairy industry because they can produce heat-stable enzymes. These enzymes may withstand various heat treatments during dairy processing, causing quality defects over the product storage period. The levels and diversity of psychrotrophic bacteria in raw milk are tightly linked to natural habitats, milking practices, and hygiene practices of farms in different countries. Most psychrotrophic bacteria can form biofilms on various milk storage and processing equipment, which serve as persistent sources of microbial contamination due to their biotransfer potential. A comprehensive review of the diversity of psychrotrophic bacteria in raw milk, the spoilage potential of these bacteria, the specific technological problems caused by biofilms and heat-resistant enzymes, and potential strategies for controlling dairy spoilage starting at the farm level is needed for improving our understanding of these spoilage bacteria. HIGHLIGHTS
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Henry, J. G., and D. Prasad. "Microbial Aspects of the Inuvik Sewage Lagoon." Water Science and Technology 18, no. 2 (February 1, 1986): 117–28. http://dx.doi.org/10.2166/wst.1986.0021.
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A facultative sewage lagoon in Inuvik, N.W.T. was studied in August (ice free) and November (ice covered) 1984. Emphasis was placed on the microbiological aspects and their relation to lagoon performance. Analyses performed included, pH, total alkalinity, total solids, suspended solids, volatile solids, COD and BOD5 determinations. The microbiological tests included total plate counts (20°C) and psychrotrophic counts (1°C). Results indicated that the Inuvik sewage lagoon system achieved removal efficiencies, ranging from 90% BOD5 removal in summer to about 80% in winter. The total bacterial count was found to decrease in the liquid of the primary cells in the winter, but the bacterial count in the secondary cell was similar under both winter and summer conditions. No significant difference existed in bacterial counts in the sludge samples between primary and secondary cells. The total bacterial number decreased by one order of magnitude in the winter in sludges from all cells. A shift from mesophilic to psychrotrophic bacteria occurred in the winter. The percentage of psychrotrophs increased from less than 1% to over 80% with the change in season. The role of psychrotrophs in lagoon performance is discussed.
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NORTJÉ, G. L., L. NEL, E. JORDAAN, K. BADENHORST, G. GOEDHART, W. H. HOLZAPFEL, and R. J. GRIMBEEK. "A Quantitative Survey of a Meat Production Chain to Determine the Microbial Profile of the Final Product." Journal of Food Protection 53, no. 5 (May 1, 1990): 411–17. http://dx.doi.org/10.4315/0362-028x-53.5.411.
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Samples from carcasses, personnel surfaces, equipment, and minced meat, packaged and displayed in cabinets were taken at a city abattoir, a wholesaler, and 10 different supermarkets. Bacteria enumerated were 1) psychrotrophs; 2) Enterobacteriaceae; 3) enterococci; 4) micrococci; 5) Pseudomonas spp; and 6) Brochothrix thermosphacta. The non integrated production system of abattoirs, wholesalers, and retailers yielded psychrotrophic and enterococci counts at retail which compared fairly well with those reported in literature, while the Enterobacteriaceae and micrococci counts were higher. Besides the psychrotrophs the pseudomonads were the most numerous group in the final product. Different surfaces were not sanitized with the same efficacy, while a general tendency towards lower counts at one supermarket group was monitored. The counts described 96% of the variation in the psychrotrophic count at the abattoir, while the success in using these counts in estimating the psychrotrophic count at the wholesaler and retailers was not as significant. At the abattoir the Enterobacteriaceae and psuedomonads were the biggest contributors to the psychrotrophic count, at the wholesaler the Enterobacteriaceae and micrococci counts, and at the retailers the micrococci and pseudomonads respectively. This indicates that Enterobacteriaceae might be common psychrotrophs in the meat production chain, maybe originating from the abattoir and wholesale environments.
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BOULARES, MOUNA, LOBNA MEJRI, and MNASSER HASSOUNA. "Study of the Microbial Ecology of Wild and Aquacultured Tunisian Fresh Fish." Journal of Food Protection 74, no. 10 (October 1, 2011): 1762–68. http://dx.doi.org/10.4315/0362-028x.jfp-11-057.
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Eighty samples of fresh fish were collected in Tunisia and analyzed for microbial load. Quality and hygienic safety of the meat and intestines of wild and aquacultured fresh fish were determined. The mesophilic aerobic plate count and populations of psychrotrophic lactic acid bacteria (LAB) and other psychrotrophic bacteria ranged from 5.67 to 7.29, 4.51 to 6, and 5.07 to 6.21 log CFU/g, respectively. For all microbiological determinations, bacterial counts were lower in meat than in the intestines of fresh fish. For all samples lower microbial populations were found in most of the wild fish than in the aquacultured fish. No isolates of the pathogenic genera Salmonella and Listeria were detected in any sample. Among the 160 strains of biopreservative psychrotrophic LAB and the 150 strains of spoilage psychrotrophic gram-negative bacteria identified by biochemical and molecular methods, Lactobacillus (six species) and Pseudomonas (six species) predominated. Lactococcus, Leuconostoc, Carnobacterium (C. piscicola and C. divergens), Aeromonas, and Photobacterium were the most common genera, and Lactococcus lactis, Lactobacillus plantarum, Pseudomonas fluorescens, and Aeromonas hydrophila were the most common species. These findings indicate that the microbiological quality of fresh fish in Tunisia can be preserved by controlling pathogenic and psychrotrophic bacteria.
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TATINI, S. R., P. MEKALA, A. EL-HABAZ, and M. W. GRIFFITHS. "Rapid Detection of Psychrotrophic Bacteria In Manufacturing Grade Raw Milks." Journal of Food Protection 54, no. 11 (November 1, 1991): 861–67. http://dx.doi.org/10.4315/0362-028x-54.11.861.
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Methods to rapidly assess the bacteriological quality of raw milk were investigated. Whereas direct microscopic count, modified psychrotrophic plate count, and direct epifluorescent filter technique (DEFT) did not correlate well with initial psychrotrophic bacterial count of raw milk, improvements were obtained after preincubation of the milk samples. The best preincubation conditions were identified as 30°C for 6 h, 21°C for 10 h, 13°C for 15 h, 13°C for 20 h, or 7°C for 37 h. The “square root” equation was applied to the data, and a model was produced for predicting growth of the native microflora of raw milk. Using this equation, a DEFT count after preincubation of the milk at 21°C for 10 h could accurately predict the initial psychrotroph count and the count after storage of the milk at 6°C for 48 h.
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Suárez, Beatriz, Carlos M. Ferreirós, and Maria-Teresa Criado. "Adherence of psychrotrophic bacteria to dairy equipment surfaces." Journal of Dairy Research 59, no. 3 (August 1992): 381–88. http://dx.doi.org/10.1017/s002202990003065x.
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SummaryPsychrotrophic bacteria isolated from raw milk were tested for their ability to adhere to steel, two types of rubber, and glass, materials employed in the construction of milking equipment. The adherence assays were carried out by exposure of the materials to radioactively labelled bacteria in both a buffering solution (Ringer's) and milk. The degree of adherence of Gram-positive bacteria was lower (P< 0·001) than that of Gram-negative bacteria. Glass was the material least prone to bacterial adherence (P< 0·001); there were no significant differences between the other three materials. Milk was found to inhibit adhesion significantly (P< 0·05), this inhibition being more evident with the most adherent bacteria. There was no statistically significant correlation between bacterial surface hydrophobicity and adherence. Our results suggest that intrinsic bacterial adherence cannot be considered a relevant factor in the contamination of milking equipment.
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MEER, R. R., J. BAKER, F. W. BODYFELT, and M. W. GRIFFITHS. "Psychrotrophic Bacillus spp. in Fluid Milk Products: A Review." Journal of Food Protection 54, no. 12 (December 1, 1991): 969–79. http://dx.doi.org/10.4315/0362-028x-54.12.969.
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Psychrotrophic bacteria have been recognized as a recurring problem in the refrigerated storage and distribution of fluid milk and cream and other perishable dairy products for several decades. Much emphasis has been focused on postpasteurization contaminants that are psychrotrophic, (e.g., Pseudomonas, Flavobacterium, and Alcaligenes spp.). Common sources of these gram-negative, non-sporeforming organisms are equipment surfaces and water supplies. Although these organisms are generally heat sensitive, many of their associated proteinases and lipases can withstand moderate to severe heat treatments and cause product deterioration. With the advance of improved control of postpasteurization contamination by nonheat-resistant psychrotrophs, more recent attention has been directed at psychrotrophic sporeformers and their potential impact on milk quality and shelf life properties. Heat-resistant psychrotrophs include members from the genera Clostridium, Arthrobacter, Microbacterium, Streptococcus, Corynebacterium, and Bacillus. However, the predominant microorganisms which comprise this category are Bacillus species. These bacteria can be introduced into milk supplies from water, udder and teat surfaces, or from soil and milkstone deposits on farm bulk tanks, pumps, pipelines, gaskets, and processing equipment. There is speculation that they can also be postpasteurization contaminants. When in the spore state, these microorganisms easily survive the typical range of pasteurization conditions with subsequent germination and outgrowth of vegetative cells. These organisms produce degradative enzymes (e.g., proteinases, lipases, and phospholipases) similar to those of non-sporeforming psychrotrophs. Enzymatic activity results in the development of objectionable flavor and quality defects in dairy products. The unique combination of both heat-resistant and psychrotrophic properties with the same microorganism represents substantial potential for causing spoilage of perishable milk products. Recent trends of higher pasteurization temperatures and extended refrigerated storage time of both raw and pasteurized milk and cream products exacerbates the significance of this group of microorganisms for the dairy foods industry.
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Salata, V. "Characteristics of the composition of the psychrotrophic microflora of frozen beef in the process of storage." Scientific Messenger of LNU of Veterinary Medicine and Biotechnologies 20, no. 83 (March 2, 2018): 308–13. http://dx.doi.org/10.15421/nvlvet8362.
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In the technological process of obtaining raw materials and food products, the main task is to ensure their safety. During the curing of beef meat, the risks are most often associated with microbial contamination. The purpose of the work was to investigate the dynamics of quantitative content and generic composition of psychrotrophic microflora in the process of storage of frozen beef with different initial microbial sowing. The investigated samples were divided into four groups, depending on the initial content of the psychrotrophic microflora. The first group of psychrotrophic microorganisms was up to 103 CFU/cm3 from the surface; second group of 103 to 104 CFU/cm3 of washed away; the third – from 104 to 105 CFU/cm3 of washed away; the fourth is more than 105 CFU/cm3 of washed away. It was established that during the storage of beef in the frozen state, the rate of development of the psychrotrophic microflora is 3,0-32,6 times faster than the mesophilic microflora. Also it was found the higher the initial microbial sowing of beef, the faster the pace of development of the microflora in the process of storing meat in the frozen state. Therefore, when choosing meat storage conditions (temperature, term), the initial microbial contamination of the carcass surface with a psychrotrophic microflora is important. It was found that from beef with low microbial sowing it is allocated three classes of psychrotrophic bacteria: Acinetobacter, Alcaligenes i Pseudomonas. The largest part of the cooled meat was 56.2 ± 2.4% of the genus Acinetobacter, and the smallest 12.5 ± 0.8% Pseudomonas. After 20 days of storage of beef in the frozen state, the growth of bacteria of the genus Pseudomonas was 1,4 times (P ≤ 0.05) due to the reduction of the Acinetobacter species of microorganisms. At the same time, the bacteria of the genus Alcaligenes were stably high in both frosty and frozen meat – 31.2–32.7%, respectively. Identification of psychrotrophic microflora with an initial content of mesophilic and psychrotrophic microorganisms 6.5 ± 0.5×103 and 4.2 ± 0.2×103 CFU/cm3 of the washed away, has established an increase in the number of identified genera. Among the already identified three genera in the washed away from beef of this group, bacteria of the genus Flavobacterium i Aeromonas are isolated, both in frozen meat and after storage in a frozen state. When identifying a psychrotrophic microflora with a significant initial microbial sowing (the number of mesophilic bacteria is greater than 5.9 ± 0.4 × 104 and psychrotrophic 3.7 ± 0.2×104 CFU/cm3 washed away the surface) was established an increase in generic composition. Thus, in the psychrotrophic microflora, 5 to 10% of bacteria of the Enterobacteriaceae genus, gram-positive sticks and cow's bacterial forms began to stand out from 3 to 5%. Consequently, the conducted searches have found that with an increase in the initial microbial contamination of beef, the quantitative genetic composition of the psychrotrophic microflora increases. As a result, the storage period of frozen beef and the hygienic and technological quality of meat is reduced.
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Picard, Catherine, Isabelle Plard, Dominique Rongdaux-Gaida, and Jean-Claude Collin. "Detection of proteolysis in raw milk stored at low temperature by an inhibition ELISA." Journal of Dairy Research 61, no. 3 (August 1994): 395–404. http://dx.doi.org/10.1017/s0022029900030818.
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SummaryAn inhibition ELISA (enzyme-linked immunosorbent assay) was developed for the determination of caseinomacropeptide (CMP) in order to estimate the proteolysis of κ-casein due to the enzymes of psychrotrophic bacteria in bulk raw milk. The CMP present in milk was quantified specifically by an antibody. The limit of detection was ∽ 0·1 μg/ml and the CV was < 10%. This method was used to study the proteolytic activity of three strains of psychrotrophic Pseudomonas fluorescens in raw milk and to analyse different raw milk samples supplied by four dairy plants. The proteolytic activity for different strains of psychrotrophs and for different milk samples varied considerably, but no correlation was established between the level of microbial flora and κ-casein proteolysis. It is thus not possible to determine the extent of proteolysis from the bacterial count alone. However, by CMP determination in bulk raw milk samples after 6 d storage at 4°C, the mean κ-casein proteolysis was ∽ 4%. Among the milk samples analysed that contained < 107 cfu psychrotrophs/ml, 30% exhibited a proteolysis of κ-casein < 0·5%, i.e. < 5μg CMP/ml.
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BYRNE, R. D., J. R. BISHOP, and J. W. BOLING. "Estimation of Potential Shelf-life of Pasteurized Fluid Milk Utilizing a Selective Preliminary Incubation." Journal of Food Protection 52, no. 11 (November 1, 1989): 805–7. http://dx.doi.org/10.4315/0362-028x-52.11.805.
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Selective preliminary incubation, followed by bacterial enumerations or detection techniques, was used to indicate potential shelf-life of pasteurized fluid milk. Commercial whole milk samples, stored at 7°C, were analyzed for bacterial and biochemical parameters and potential shelf-life using daily organoleptic evaluation. Prior to analysis, each sample was subjected to the following preliminary incubations: milk alone, milk with benzalkonium chloride, milk and broth, milk and broth with benzalkonium chloride, and milk and a dairy gram-negative broth. The following bacterial enumerations were conducted: Psychrotrophic Bacteria Count, modified Psychrotrophic Bacteria Count (Petrifilm and agar methods), and Moseley Keeping Quality test (Petrifilm and agar methods). Catalase detection (headspace pressure and flotation time) and impedance detection times were also determined. Initial Standard Plate and Coliform counts (Petrifilm and agar methods) were conducted on each fresh sample but were not used for shelf-life prediction. Many of the preliminary incubations, in conjunction with enumeration or detection combinations, (especially modified Psychrotrophic Bacteria Count and impedance microbiology) gave good correlations to shelf-life (−0.89 and 0.91, respectively). Thus, these methods could be used to indicate the potential shelf-life of pasteurized fluid milk.
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Cempírková, R., and M. Mikulová. "Incidence of psychrotrophic lipolytic bacteria in cow’s raw milk." Czech Journal of Animal Science 54, No. 2 (February 18, 2009): 65–73. http://dx.doi.org/10.17221/1667-cjas.
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The contamination of bulk samples of cow’s raw milk (<I>n</I> = 491) by psychrotrophic lipolytic bacteria (PLiBC), total count of psychrotrophic bacteria (PBC) and mesophilic bacteria (TBC) was monitored for two years on eight dairy farms and the correlations among these groups of bacteria were analysed. An increase in TBC, PBC and PLiBC and in the values of free fatty acids (FFA) was tested experimentally in three milk samples in relation to time (analyses were done in 24-hour intervals until 96 hours) and storage temperature of milk samples (4; 6.5 and 10°C). Bacterial contamination of milk was determined by culture methods in accordance with IDF standards, the values of FFA were determined by an extraction-titration method. These mean values were determined in the set of samples (<I>n</I> = 491): PLiBC 659 CFU/ml, PBC 2 932 CFU/ml and TBC 18 932 CFU/ml. A high correlation was proved between values of PBC and PLiBC (<I>r</I> = 0.87; <I>P</I> < 0.001) while the correlation between TBC and PBC (<I>r</I> = 0.65; <I>P</I> < 0.001) and between PLiBC and TBC (<I>r</I> = 0.59; <I>P</I> < 0.001) was on a medium level. The proportional index <I>p<sub>I</sub></I> for PLiBC/PBC was 0.20, for PLiBC/TBC 0.03 and for PBC/TBC 0.16. In seasonal dynamics a statistically significant difference (<I>P</I> < 0.001; <I>P</I> < 0.05) between the increased values of TBC in the summer season was proved compared to the winter and spring season. The differences in the seasonal variation of PBC and PLiBC values were not significant. Experimental investigation of an increase in the values of tested parameters showed that at temperatures of milk sample storage 4 and 6.5°C TBC did not exceed the permissible hygienic value (100 000 CFU/ml) even after 96 hours while at 10°C it amounted to 90 000 CFU/ml after 48 hours and the limit for TBC was exceeded several times after 96 hours. PBC, which is not inhibited by cold storage to such a large extent, did not exceed the hygienic limit value for PBC (50 000 CFU/ml) even after 96 hours when milk samples were stored at 4°C, but at 6.5°C after 72 hours and at 10°C already after 48 hours the values 6 and 20 times higher, respectively, than the hygienic limit were recorded. A similar trend was observed in PLiBC, which exceeded the hazardous limit (43 000 CFU/ml) at 6.5°C after 96 hours and at 10°C already after 48 hours whereas at 4°C the limit value was not exceeded even after 96 hours. The content of FFA also increased in relation to the storage time and temperature of milk samples but in comparison with the increase in the tested groups of microorganisms the increase in FFA showed a higher correlation with storage time compared to storage temperature. A medium correlation was calculated between PLiBC and/or PBC and FFA content (<I>r</I> = 0.52; <I>r</I> = 0.57; <I>P</I> < 0.001).
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Bashir, Ahmad, Javed Imran, Ali Shah Aamer, Hameed Abdul, and Hasan Fariha. "Psychrotrophic bacteria isolated from -20C freezer." African Journal of Biotechnology 9, no. 5 (February 1, 2010): 718–24. http://dx.doi.org/10.5897/ajb09.1613.
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Ruas-Madiedo, Patricia, Juan Carlos Bada-Gancedo, Teresa Delgado, Miguel Gueimonde, and Clara G. de los Reyes-Gavilán. "Proteolysis in rennet-coagulated Spanish hard cheeses made from milk preserved by refrigeration and addition of carbon dioxide." Journal of Dairy Research 70, no. 1 (February 2003): 115–22. http://dx.doi.org/10.1017/s0022029902005952.
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On-farm refrigeration of milk reduces the growth rate of mesophilic bacteria so allowing longer storage time of raw milk before processing. However, refrigeration creates a selective pressure favouring the multiplication of psychrotrophic bacteria present as normal contaminants in raw milk. Psychrotrophs are killed by most of the currently employed pasteurization and sterilization treatments of milk but they can produce extracellular heat-stable proteinases and lipases, which are capable of degrading various milk components, affecting the storage-life of heat-processed milk and the quality of dairy products (Champagne et al. 1994; Shah, 1994).
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DELAQUIS, P. J., C. GARIÉPY, and FRANCE DUSSAULT. "Bacteriology of Hot and Cold Boned Pork Preblends." Journal of Food Protection 55, no. 11 (November 1, 1992): 910–12. http://dx.doi.org/10.4315/0362-028x-55.11.910.
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Ground pork and preblends containing 2% NaCl or 2% NaCl plus 200 ppm NaNO2 were prepared from hot (HB) and cold (CB) boned pork in a commercial slaughtering plant. Total aerobic mesophiles, psychrotrophs, Enterobacteriaceae, salt tolerant, and lactic acid bacteria were enumerated in freshly ground meat and in preblends stored for 1 week at 2°C. Boning method had no effect on mesophillic, psychrotrophic, and salt tolerant counts in freshly ground meat, but Enterobacteriaceae and lactic acid bacteria were found in higher numbers in CB than HB meat (P < 0.05). Addition of salt plus nitrite led to the inhibition of most bacterial groups, although lactic acid bacteria were found in higher numbers in HB preblends after one week of storage (P < 0.05). The data revealed that HB pork preblends of excellent bacteriological quality and stability can be produced in an industrial context.
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BYRNE, ROBERT D., and J. RUSSELL BISHOP. "The Limulus Amoebocyte Lysate Assay and the Direct Epifluorescent Filter Technique as Estimators of Potential Shelf-life of Pasteurized Fluid Milk." Journal of Food Protection 53, no. 2 (February 1, 1990): 151–53. http://dx.doi.org/10.4315/0362-028x-53.2.151.
Full textAbstract:
The Limulus Amoebocyte Lysate Assay, Direct Epifluorescent Filter Technique and modified Psychrotrophic Bacteria Count were used to indicate potential shelf-life of pasteurized fluid milk. Commercial whole milk samples, stored at 7°C, were analyzed for bacterial and biochemical parameters, as well as for potential shelf-life by daily sensory evaluation. Each sample was evaluated before and after the following preliminary incubations: milk alone, milk with benzalkonium chloride, milk and broth, and milk and broth with benzalkonium chloride. The Limulus Amoebocyte Lysate Assay, Direct Epifluorescent Filter Technique, and modified Psychrotrophic Bacteria Count in conjunction with the preliminary incubations, produced relatively high correlations to shelf-life (−0.78, −0.85, and −0.86 respectively). Thus, these bacterial detection techniques could be used as rapid methods of shelf-life estimation.
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ŚMIECIŃSKA, KATARZYNA. "Microbiological quality of beef stored under different modified atmospheres." Medycyna Weterynaryjna 76, no. 12 (2020): 6471–2020. http://dx.doi.org/10.21521/mw.6471.
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The aim of this study was to analyze changes in the microbiological quality of Longissimus lumborum (LL) muscles collected from young Polish Holstein-Friesian Black-and-White (PHF BW) bulls and stored for 7, 14, and 21 days under different modified atmospheres (MA) (vacuum, 80% O2 + 20% CO2, 60% O2 + 30% CO2 + 10% N2, 40% CO2 + 60% N2, 30% CO2 + 70% Ar). Before and after the specified storage periods, crosssectional samples of the LL muscle were collected under aseptic conditions to determine total microbial counts, and the total counts of psychrotrophic bacteria and mesophilic lactic acid bacteria. The effects of storage time and MA composition on changes in the parameters analyzed were evaluated, and the effectiveness of argon in delaying microbial growth in cold-stored beef was determined. Between days 7 and 14 of storage, total microbial counts were lowest in meat packaged under the MA composed of 30% CO2 + 70% Ar, whereas between days 14 and 21 they were lowest in both MA packages containing O2. The greatest increase in total microbial counts between days 7 and 14 of storage was noted in the MAs containing O2, and between days 14 and 21 of storage in the MA containing Ar. Beef stored for 7 days in the MA containing 60% O2 was characterized by the lowest total microbial counts, whereas the highest total microbial counts were noted in samples stored for 14 days in the MA containing 80% O2. Between days 7 and 14 of storage, the counts of psychrotrophic bacteria increased significantly in all MAs. Between days 14 and 21 of storage, the counts of psychrotrophic bacteria did not increase in meat samples packaged under vacuum or the MA composed of 80% O2 + 20% CO2. The counts of psychrotrophs were significantly lower in beef stored for 7 days in the oxygen-free MAs than they were in both MA packages containing O2. The counts of psychrotrophic bacteria were significantly lower in beef stored for 14 days in the MA containing Ar, compared with samples packaged under vacuum and the MA containing 80% O2. Gas composition in MA packaging had no significant effect on total microbial counts or the counts of psychrotrophic bacteria in meat stored for 21 days. Between days 14 and 21 of storage, the counts of lactic acid bacteria did not increase significantly only in meat packaged in the MAs composed of 60% O2 + 30% CO2 + 10% N2 and 40% CO2 + 60% N2. After 7 days of storage, the counts of lactic acid bacteria were higher in beef packaged in oxygen-free MAs than they were in both MA packages containing O2. After 14 days of storage, the counts of lactic acid bacteria were higher in meat packaged in the MA composed of 80% O2 + 20% CO2 than they were in the other MAs. Beef samples stored for 21 days under the MA composed of 80% O2 + 20% CO2 were characterized by significantly lower counts of lactic acid bacteria, compared with samples stored under the other MAs, except for the MA composed of 40% CO2 + 60% N2. It can be concluded that beef can be stored in the MA composed of 30% CO2 + 70% Ar for shorter periods of time (up to 14 days). The modified atmosphere composed of 30% CO2 + 70% Ar contributed to slower microbial growth in meat and resulted in lower counts of psychrotrophs and lactic acid bacteria, relative to the other samples. However, there is a need for further research on different concentrations of argon in MA packages to confirm that this gas can effectively delay microbial growth in beef. Meat stored for 14 days in the MA composed of 80% O2 + 20% CO2 was characterized by the lowest microbiological quality. The composition of MAs had a minor influence on the growth rates of the microbial groups analyzed in beef stored for 21 days; certain changes were observed only in the counts of lactic acid bacteria.
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JAY, JAMES M., and MAY E. BUE. "Ineffectiveness of Crystal Violet Tetrazolium Agar for Determining Psychrotrophic Gram-Negative Bacteria." Journal of Food Protection 50, no. 2 (February 1, 1987): 147–49. http://dx.doi.org/10.4315/0362-028x-50.2.147.
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Gram-negative psychrotrophic and nonpsychrotrophic mesophiles grew equally well on crystal violet tetrazolium (CVT) agar at 30°C in 48 h, hence this medium is not suitable for enumerating or recognizing psychrotrophic bacteria.
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Capita, R., C. Alonso-Calleja, M. T. García Arias, B. Moreno, and M. C. García-Fernández. "Note. Effect of trisodium phosphate on mesophilic and psychrotrophic bacterial flora attached to the skin of chicken carcasses during refrigerated storage Nota. Efecto del fosfato trisódico en los microorganismos mesófilos y psicrotrofos presentes en la piel de canales de pollo durante su almacenamiento en refrigeración." Food Science and Technology International 6, no. 4 (August 2000): 345–50. http://dx.doi.org/10.1177/108201320000600410.
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The potential for using trisodium phosphate (TSP) to reduce mesophilic and psychrotrophic popula tions on the skin of chicken carcasses was explored. Skin samples were immersed in sterile tap water (control) or an 8%, 10% or 12% solution of TSP at 20 °C for 15 min. Surface pH values and mesophilic and psychrotrophic plate counts were determined after 0, 1, 3 and 5 days of storage at 2° C. After washing, bacterial populations were significantly smaller in the samples treated with TSP than in the controls. The concentration of the TSP solution was a significant factor in reducing the populations of the bacteria on chicken skin. Before storage, the reduction in the presence of bacteria achieved in treated samples with respect to controls ranged between 0.95 log10 cycles and 1.78 log10 cycles in the case of mesophilic microorganisms, and 0.92 log10 cycles and 1.94 log10 cycles in the case of psychrotrophic strains. These differences between the concentrations of bacteria in samples immersed in water and those treated with TSP increased over time, ranging from 2.35 log 10 cycles to 3.08 log10 cycles (mesophilic microorganisms), and from 2.79 log10 cycles to 4.09 log10 cycles (psychrotrophic microorganisms) on day 5 of storage. The pH of the skin remained more or less constant throughout the study period, ranging between 8 and 9 in skin treated with TSP, depending on the concentration, while it was two units lower in the control samples.
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BISHOP, J. R., and C. H. WHITE. "Estimation of Potential Shelf-life of Pasteurized Fluid Milk Utilizing Bacterial Numbers and Metabolites." Journal of Food Protection 48, no. 8 (August 1, 1985): 663–67. http://dx.doi.org/10.4315/0362-028x-48.8.663.
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A study was conducted on use of bacterial numbers and their metabolites, and any possible interaction thereof, as estimators of the potential shelf-life of pasteurized fluid milk. Whole and skim milk samples were obtained on the day of processing. Samples of each milk were inoculated in duplicate with 0, 1,000, or 100,000 bacteria/ml with a pure strain of Pseudomonas fluorescens P27. Samples, stored at 7°C, were analyzed for microbiological and bioichemical parameters every 5 d for up to 20 d, with organoleptic evaluations conducted on a daily basis. On days of analysis, each sample was subjected to various preliminary incubations. Bacterial enumerations conducted were psychrotrophic bacteria count, standard plate count, gram-negative bacteria count, and modified psychrotrophic bacteria count. Lipopolysaccharide (endotoxin) concentrations, degree of proteolysis and impedance detection were also determined. All bacterial enumerations and proteolysis were significantly related to potential shelf-life of pasteurized fluid milk (whole, skim, and combined) but were of little predictive value. Endotoxin concentration and impedance detection were highly significantly related to shelf-life, and provided predictive regression equations. Using combined data from whole and skim milk, impedance detection resulted in the preferred prediction equation suitable for pasteurized fluid milks.
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GREER, G. GORDON, and BRYAN D. DILTS. "Enumeration of Meatborne Spoilage Bacteria with Hydrophobic Grid Membrane Filtration†." Journal of Food Protection 60, no. 11 (November 1, 1997): 1388–90. http://dx.doi.org/10.4315/0362-028x-60.11.1388.
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Hydrophobic grid membrane filtration (HGMF) was investigated as an alternative to conventional plate counts for enumerating spoilage bacteria recovered from raw beef. The HGMF method was compared to conventional procedures for the selective enumeration of total psychrotrophic bacteria, pseudomonads, total Enterobacteriaceae. Brochothrix thermosphacta, and lactic acid bacteria. Bacteria were recovered both from beef which had been artificially inoculated with identified strains and from naturally contaminated beef from a commercial abattoir. There were no significant differences (P > 0.05) in numbers of any bacterial group recovered from naturally contaminated beef using HGMF procedures when compared to conventional plating on selective media. The recoveries of the total psychrotrophic population, Escherichia coli. B. thermosphacta, and Lactobacillus sake inoculated onto meat were unaffected by the enumeration procedure (P > 0.05). However, the populations of Pseudomonas sp. recovered from inoculated beef by a HGMF procedure were 0.8 log cycles lower (P < 0.05) when compared to the conventional spread plate procedure.
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DAHER, N. SAYEM EL, and R. E. SIMARD. "Putrefactive Amine Changes in Relation to Microbial Counts of Ground Beef During Storage." Journal of Food Protection 48, no. 1 (January 1, 1985): 54–58. http://dx.doi.org/10.4315/0362-028x-48.1.54.
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Seven amines currently found in ground beef, 1,3 diaminopropane, histamine, cadaverine, putrescine, spermine, spermidine and tyramine, were evaluated as indicators of total bacterial, psychrotrophic and coliform counts in raw ground beef stored for 12 d at 4, 7 and 10°C. At 2-d intervals, amines were analyzed by extraction with 0.6 N HC104, separation by ion exchange column chromatography, and detection by ninhydrin. Lysine decarboxylase positive bacteria (LD+) during storage at 4°C were also studied. Correlation and regression analysis were used to determine the relationship of amine concentration to bacterial count. The percentage of lysine decarboxylase-positive bacterial colonies increased until the 6th day of storage and then decreased until the 12th day. Total and psychrotrophic bacterial counts ranged from 102 to 109 bacteria/g and were correlated significantly with putrescine, 1,3 diamino-propane, tyramine, cadaverine and spermidine. Cadaverine was the only amine that correlated significantly with coliforms (P≥0.95).
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JEONG, DONG K., and JOSEPH F. FRANK. "Growth of Psychrotrophic Bacteria in Solids Fortified Skim Milk." Journal of Food Protection 51, no. 8 (August 1, 1988): 643–47. http://dx.doi.org/10.4315/0362-028x-51.8.643.
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The effect of fortifying skim milk with non-fat dried milk on growth and proteolysis of psychrotrophic bacteria was determined. Raw skim milk of 8.7% total solids was fortified to 10% and 12% total solids and pasteurized. Growth rates of proteolytic psychrotrophic bacteria were determined in these milks during incubation at 4°C. Proteolysis was determined by measuring the concentration of free amino groups throughout the incubation period. Seven of nine psychrotrophic isolates grew to greater numbers in the fortified milks during the early log phase of growth than they did in the unfortified milks. Growth stimulation was slight in most cases, however, one isolate exhibited a ten-fold increase in numbers when growing in the 10% solids fortified milk. The greatest increases in growth were observed when comparing unfortified milk to milk at 10% solids. Early log phase growth in 12% solids milk was often less than in 10% solids milk but still greater than in unfortified milk. All isolates exhibited increased proteolysis in the fortified milks within 48 h of incubation. These results indicate that increasing the solids content of skim milk with non-fat milk powder produces a microbiological growth medium more suitable for growth and protease production for selected psychrotrophic bacteria.
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Sinha, Nupur. "Psychrotrophic Bacteria: A Boonto Higher Altitude Agriculture." Indian Journal of Agricultural Biochemistry 32, no. 1 (2019): 10. http://dx.doi.org/10.5958/0974-4479.2019.00002.9.
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Margesin, Rosa, Norbert Palma, Franz Knauseder, and Franz Schinner. "Proteases of psychrotrophic bacteria isolated from glaciers." Journal of Basic Microbiology 31, no. 5 (1991): 377–83. http://dx.doi.org/10.1002/jobm.3620310515.
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LUTGRING, K. R., R. H. LlNTON, N. J. ZIMMERMAN, M. PEUGH, and A. J. HEBER. "Distribution and Quantification of Bioaerosols in Poultry-Slaughtering Plantst†." Journal of Food Protection 60, no. 7 (July 1, 1997): 804–10. http://dx.doi.org/10.4315/0362-028x-60.7.804.
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Four poultry-slaughtering plants (2 turkey, 2 duck) were investigated for airborne concentration of microorganisms, including mesophilic and psychrotrophic bacteria and yeasts and molds. Approximately 40 sites were sampled in each plant during four visits (fall, winter, spring, and summer) by using an Anderson N-6 Air Sampler containing either tryptic soy agar (for mesophilic and psychrotrophic bacteria), or Rose Bengal agar (for yeasts and molds). Sampling sites inside the plants were categorized into the following areas: shackling, picking, evisceration, post chiller, cut-up, portion packaging and whole bird packaging. Areas outside the plant were sampled as controls. Airborne microbial counts in each plant were highest in shackling areas and decreased toward the packaging areas. Bacteria were the most common airborne microorganisms identified. In general, mesophilic bacterial counts ranged from an average high of 6 log CFU/m3 in shackling to an average low of 2.5 log CFU/m3 outside the plant. Mean psychrotrophic bacterial levels were usually within 1 log unit (90%) less than mesophilic bacterial levels and ranged from 2.5 to 5 log CFU/m3 Yeasts and molds typically represented only a small proportion of the microbial population and usually were between 2.5 to 4 log CFU/m3 Air flow, distribution, temperature, relative humidity, and design of the slaughtering facility were all important factors affecting overall bioaerosol contamination. This study identified the sources and concentrations of bioaerosols that may affect product safety and shelf life. This information is useful for developing appropriate strategies for poultry-slaughtering plant design.
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VENUGOPAL, RAVEENDRAN J., and JAMES S. DICKSON. "Growth Rates of Mesophilic Bacteria, Aerobic Psychrotrophic Bacteria, and Lactic Acid Bacteria in Low-Dose–Irradiated Pork." Journal of Food Protection 62, no. 11 (November 1, 1999): 1297–302. http://dx.doi.org/10.4315/0362-028x-62.11.1297.
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Frozen pork patties, thawed overnight at 0°C or temperature abused through storage at 15°C for 24 h, were packaged using both vacuum and air packaging methods. Immediately after packaging, both sets of patties were irradiated at 0, 0.5, 1, and 2 kGy. All the samples were stored at 2°C and were analyzed for populations of mesophilic, psychrotrophic, and lactic acid bacteria every 3 days for 30 days. By using a mesophilic population of 107 cells/g as a criteria for spoilage, fresh pork patties receiving a dose of 0 kGy had shelf lives of 11 and 16 days with air and vacuum packaging methods, respectively, whereas temperature-abused patties had a shelf life of 7 days with both air and vacuum packaging methods. Both fresh and abused patties that received a dose of 2 kGy had shelf lives that were greater than 30 days at 2°C with both air and vacuum packaging methods. Descriptive models based on the Gompertz equation for mesophilic, psychrotrophic, and lactic acid bacteria were developed, and the generation time and lag-phase duration for each bacterial population were calculated.
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CHRISTEN, GENEVIEVE L., and M. SENICA. "Casein, Fluorescein Isothiocyanate as a Substrate for Measuring Protease Production by Psychrotrophic Bacteria." Journal of Food Protection 50, no. 9 (September 1, 1987): 744–49. http://dx.doi.org/10.4315/0362-028x-50.9.744.
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Fluorescein isothiocyanate-labelled casein was evaluated as a substrate for measuring bacterial protease activity in milk. Using protease from Bacillus amyloliquefaciens, effects of substrate type, pH, temperature and enzyme concentration were determined. The procedure was sensitive to .012 unit of enzyme activity. The procedure was then used as a method to detect protease production by psychrotrophic bacteria growing in pasteurized skim milk at 7°C for 5 d. Three psychrotrophic bacteria were added at three different initial populations. Bacterial population, protease activity and cumulative free amino groups were monitored daily. Bacterial populations were not correlated with either protease activity or cumulative free amino groups. Pro-tease activity and cumulative free amino groups were correlated (r=.46, p=.001). Both protease activity and cumulative free amino groups peaked as the microorganisms entered the late log phase (approximately 108 colony forming units per ml). This occurred after incubation for 2 d at 7°C in two replications and after 3 d in the third. Both values decreased with continued storage.
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Cempírková, R. "Psychrotrophic vs. total bacterial counts in bulk milk samples." Veterinární Medicína 47, No. 8 (March 30, 2012): 227–33. http://dx.doi.org/10.17221/5829-vetmed.
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The objective of the study was to determine psychrotrophic bacteria counts (PBC) and total bacterial counts (TBC) in bulk milk samples collected during a longer period (1999 to 2000). Two sets of samples were analysed. Set 1, including samples collected in three herds, was analysed by the Central Laboratory at České Budějovice. TBC was determined using the apparatus Bactoscan, and PBC by culture according to IDF standards. Relative index pi expressing the PBC/TBC ratio was calculated for each sample. The value of pi for Set 1 was 0.09, ranging in herds included in this set from 0.05 to 0.20. The correlation between PBC and TBC was highly significant (r = 0.69; P < 0.01). Correlation coefficients for the individual herds ranged from 0.32 to 0.81. The correlation was highly significant (P < 0.01) in two herds, and significant (P < 0.05) in one herd. Microbiological milk quality is markedly influenced by housing and milking technologies. Another objective of this study was therefore to compare the microbiological quality of milk produced by cows housed in loose boxes and milked in parlours with that produced by cows housed in stanchion barns and milked with pipeline milking machines (Set 2). Bulk milk samples were collected and transported by standard methods and TBC and PBC were determined by culture on GTK agar supplemented with dried inhibitor-free milk according to the IDF standards. The results have confirmed favourable effects of milking in parlours on milk quality expressed in terms of counts of both technologically relevant groups of bacteria. The difference in TBC and PBC between the two milking technologies was significant (P < 0.05). Relative index for the milk obtained in milking parlours was pi= 0.18 and that for the milk from pipeline milking machines pi = 0.23. Correlation coefficients for PBC and TBC were almost identical (r = 0.92; r = 0.93; both P < 0.01).
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GUTIÉRREZ, ROSALBA, ISABEL GONZÁLEZ, TERESA GARCÍA, ESTER CARRERA, BERNABÉ SANZ, PABLO E. HERNÁNDEZ, and ROSARIO MARTÍN. "Monoclonal Antibodies and an Indirect ELISA for Detection of Psychrotrophic Bacteria in Refrigerated Milk." Journal of Food Protection 60, no. 1 (January 1, 1997): 23–27. http://dx.doi.org/10.4315/0362-028x-60.1.23.
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Monoclonal antibodies generated against live cells of Pseudomonas fluorescens have been used in an indirect ELISA format for the detection of Pseudomonas spp. and related psychrotrophic bacteria in refrigerated milk. The immunorecognition of monoclonal antibodies adsorbed to bacteria bound to the wells of a microtiter plate was performed with rabbit anti-mouse immunoglobulins conjugated to horseradish peroxidase. Subsequent enzymic conversion of the substrate resulted in distinct absorbance differences when assaying milk samples containing psychrotrophic bacteria in the range 105 to 109 CFU ml−1. The detection threshold for the ELISA assay developed in this work is 105 CFU ml−1.
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García-Armesto, María-Rosario, Miguel Prieto, Carlos Alonso, María-Luisa GarcíLópez, María-Camino García-Fernández, and Andrés Otero. "Numerical taxonomy of psychrotrophic bacteria isolated from raw ewes' milk." Journal of Dairy Research 60, no. 3 (August 1993): 371–83. http://dx.doi.org/10.1017/s0022029900027710.
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SummaryA total of 204 psychrotrophic isolates from raw ewes' milk (hand and machine milked) were identified by conventional methods. In addition, a numerical taxonomic study was conducted on 180 of these isolates and 19 reference strains. Three of the isolates were yeasts. Using identification schemes, 54 isolates were assigned to genera of Gram-negative aerobic rods (Pseudomonas, Acinetobacter, Flavobacterium, MoraxellaandPsychrobacter), 48 were Enterobacteriaceae (Entero-bacter, Hafnia, Klebsiella, CitrobacterandSerratia) and one was identified asAeromonas hydrophila. The 98 Gram-positive isolates were identified asEnterococcus, Streptococcus, Leuconostoc, Lactococcus, Bacillus, Staphylococcus, Micrococcus, Aureobacterium, KurthiaandMicrobacterium. At the 82% similarity level (SSM), 18 clusters were formed. Cluster I included 34 strainsof Lactococcus, StreptococcusandLeuconostoc. Most of the 35 strains in cluster II wereEnterococcus. Clusters III and IV were identified asKurthiaandMicrobacteriumrespectively. Cluster V was identified asAureobacteriumand cluster VI consisted of coagulase-negative staphylococci. Gram-negative isolates formed 12 clusters:Aeromonas(one cluster), Enterobacteriaceae (two clusters),Flavobacterium(two clusters),PseudomonasandPsychrobacter immobilis(three clusters) andAcinetobacter(four clusters). Non-motile variants ofPs. fragiwere found.Enterococcusand Enterobacteriaceae did not have significant spoilage properties. As expected, Gram-negative aerobic rods were proteolytic and/or lipolytic even at low temperature. Contamination with certain types of psychrotrophs (Gram-negative aerobic rods and enterococci) seemed to be associated with the milking method. The isolate ofAes. hydrophilahad properties associated with virulence.
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عبد المنعم, معتز عبد الواحد, نجم هادي الخزرجي, and عماد ابراهيم علي سلطان. "Role of some psychrotrophic aerobic sporeforming bacteria in spoilage of raw milk." Iraqi Journal of Veterinary Medicine 28, no. 1 (June 28, 2004): 134–46. http://dx.doi.org/10.30539/ijvm.v28i1.1073.
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This study was planned to isolated and identify some psychrotrophic aerobic sporeforming bacteria from raw milk and determine the predomenant isolate.
Microbiological estimations were performed for (100) raw milk samples collected from four sources (filters, stations, bulk tanks and milk containers) and for the same samples after heat treatment at 80°C for (12) minutes and upon subsequent storage at (7)°C for 0,7,14 and 21 days.
The Aerobic plate count (APC) was determined and the total bacterial count were compared with each of the mesophilic sporeformer count (MSFC) at (0) & (7) days of storage & the psychrotrophic sporeformer count (PSFC) upon storage at (7)°C for 0,7,14 and 21 days. Positive relationship existed between the increase in (APC) before heat treatment & the increase in (MSFC) at (0) or (7) days or (PSFC) at 0,7,14 & 21 days of storage at 7°C. Immediately after heat treatment at (80)°C for 12 minutes 59% of the samples had psychrotrophic sporeformer counts of <10 cfu/ml, but after (21) days of storage at (7)°C, 79% of the samples had counts of > 109 cfu/ml.
Bacillus cereus and Bacillus mycoides were identified as the predominant psychrotrophic sporeformers in the heated milk, stored at 7°C.
The results confirmed that growth of heat-resistant psychrotrophicsporeforming organisms co-incide with spoilage of heated milk, and was a higher than of the normal pasteurization temperatures or longer time which enhanced the germination of these spores. psychrotrophic sporeformers have been shown to be responsible for such off-flavors (bitter, stale, rancid and putrid) of heated milk stored at (7)°C for (21) days, and sweet curdling observed in 70% of the samples in the forms of "buttons” at the bottom of the containers after (21) days of storage at (7)°C.
Most of the isolated psychrotrophic B cercus were able to produce porteinase, lipases and lecithinase enzymes beside the haemolysin.
It was concluded that the number of (PSFC) in raw milk
conditions prevailing sanitary
the depends upon apparently during production and upon time and temperature of milk storage before processing.
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Janiyani, Kamala L., and M. K. Ray. "Cloning, Sequencing, and Expression of the Cold-Inducible hutU Gene from the Antarctic Psychrotrophic Bacterium Pseudomonas syringae." Applied and Environmental Microbiology 68, no. 1 (January 2002): 1–10. http://dx.doi.org/10.1128/aem.68.1.1-10.2002.
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ABSTRACT A promoter-fusion study with a Tn 5-based promoter probe vector had earlier found that the hutU gene which encodes the enzyme urocanase for the histidine utilization pathway is upregulated at a lower temperature (4° C) in the Antarctic psychrotrophic bacterium Pseudomonas syringae. To examine the characteristics of the urocanase gene and its promoter elements from the psychrotroph, the complete hutU and its upstream region from P. syringae were cloned, sequenced, and analyzed in the present study. Northern blot and primer extension analyses suggested that the hutU gene is inducible upon a downshift of temperature (22 to 4°C) and that there is more than one transcription initiation site. One of the initiation sites was specific to the cells grown at 4°C, which was different from the common initiation sites observed at both 4 and 22°C. Although no typical promoter consensus sequences were observed in the flanking region of the transcription initiation sites, there was a characteristic CAAAA sequence at the −10 position of the promoters. Additionally, the location of the transcription and translation initiation sites suggested that the hutU mRNA contains a long 5′-untranslated region, a characteristic feature of many cold-inducible genes of mesophilic bacteria. A comparison of deduced amino acid sequences of urocanase from various bacteria, including the mesophilic and psychrotrophic Pseudomonas spp., suggests that there is a high degree of similarity between the enzymes. The enzyme sequence contains a signature motif (GXGX2GX10G) of the Rossmann fold for dinucleotide (NAD+) binding and two conserved cysteine residues in and around the active site. The psychrotrophic enzyme, however, has an extended N-terminal end.
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Stannard, C. J., A. P. Williams, and P. A. Gibbs. "Temperature/growth relationships for psychrotrophic food-spoilage bacteria." Food Microbiology 2, no. 2 (April 1985): 115–22. http://dx.doi.org/10.1016/s0740-0020(85)80004-6.
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Mitchell, Gregory E., Ken N. Ewings, and John P. Bartley. "Physicochemical properties of proteinases from selected psychrotrophic bacteria." Journal of Dairy Research 53, no. 1 (February 1986): 97–115. http://dx.doi.org/10.1017/s0022029900024705.
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SUMMARYThe physicochemical properties of eight extracellular proteinases secreted by psychrotrophic bacteria of dairy origin have been studied. Seven of these proteinases were able to withstand ultra heat treatment (UHT) with D values at 140 °C ranging from 2 to 300 s. The sixPseudomonas fluorescensproteinases were glycoproteins of mol. wt 47000–49500. The twoSerratia marcescensproteinases, of mol. wt of 51000, did not contain carbohydrate but in other respects were similar to the Pseudomonas proteinases. The proteinases were inhibited by various metal chelators and all contained Ca and Zn in similar proportions. Their amino acid compositions were similar, with alanine as the N-terminal group, cysteine completely absent and very low levels of methionine. Isoelectric points ranged from 5·10 to 8·25. Their physical and chemical properties enabled them to be classified as alkaline metalloendopeptidases. A similarity index (S▵n) was used to predict sequence homology between ten proteinases of known amino acid composition. Comparisons of S▵n of these proteinases showed only minor sequence differences except for those ofPs. fluorescensMC60. Heat resistance could not be related wholly to similarities in protein sequence, but could be related both to the strength of stabilizing Ca2+–protein interactions and to the randomness inherent within the folding of the peptide chain.
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Margesin, R., and F. Schinner. "Extracellular protease production by psychrotrophic bacteria from glaciers." International Biodeterioration & Biodegradation 29, no. 2 (January 1992): 177–89. http://dx.doi.org/10.1016/0964-8305(92)90015-g.
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Munsch-Alatossava, P., and T. Alatossava. "Phenotypic characterization of raw milk-associated psychrotrophic bacteria." Microbiological Research 161, no. 4 (November 2006): 334–46. http://dx.doi.org/10.1016/j.micres.2005.12.004.
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Munsch-Alatossava, P., and T. Alatossava. "Antibiotic resistance of raw-milk-associated psychrotrophic bacteria." Microbiological Research 162, no. 2 (April 2007): 115–23. http://dx.doi.org/10.1016/j.micres.2006.01.015.
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KATOR, HOWARD, and ROBERT A. FISHER. "Bacterial Spoilage of Processed Sea Scallop (Placopecten magellanicus) Meats." Journal of Food Protection 58, no. 12 (December 1, 1995): 1351–56. http://dx.doi.org/10.4315/0362-028x-58.12.1351.
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During extended summer trips (16 days), mid-Atlantic sea scallop (Placopecten magellanicus) meats hand-shucked at sea and stowed on ice in linen bags become unmarketable because of a spoilage process called “yellowing.” Studies were performed to evaluate spoilage of shucked scallop meats by psychrotrophic bacteria under conditions of simulated and actual commercial stowage, and to examine the effects of various prestowage washes and bag materials on this process. A scallop medium and enumeration method based on measuring bacterial populations at the bag/meat interface were developed for this purpose. Results showed that large populations of psychrotrophic bacteria (> 1010 culturable cells per in2) grew on the meats and meat/bag interfaces at 2°C over a 15-day stowage period. Associated with this growth was a rise in surface pH and the appearance and gradual increase of fluorescence on cut muscle surfaces and bags under long-wave UV illumination. Freshly shucked meat surfaces never fluoresced. Of the various deck treatments and bag materials tested, only treatment with 1.25% lactic acid solution retarded pH and bacterial density increases.
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Champagne, Claude P. "Inhibition of psychrotrophic bacteria in raw milk by immobilized lactic acid bacteria." Biotechnology Letters 12, no. 10 (October 1990): 771–76. http://dx.doi.org/10.1007/bf01024738.
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