Academic literature on the topic 'Polyphenol oxidase activity (PPO)'
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Journal articles on the topic "Polyphenol oxidase activity (PPO)"
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Sabir, Dlawer M., and Basima Y. Putros. "The Role of Polyphenol Oxidase (PPO) in Antiprolactin Activity." Journal of Zankoy Sulaimani - Part A 7, no. 1 (May 28, 2003): 55–59. http://dx.doi.org/10.17656/jzs.10123.
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Escobar, Matthew A., Andrew Shilling, Pine Higgins, Sandra L. Uratsu, and Abhaya M. Dandekar. "Characterization of Polyphenol Oxidase from Walnut." Journal of the American Society for Horticultural Science 133, no. 6 (November 2008): 852–58. http://dx.doi.org/10.21273/jashs.133.6.852.
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The enzyme polyphenol oxidase (PPO) is nearly ubiquitous in Kingdom Plantae and catalyzes the oxidation of phenolic compounds into highly reactive quinones. Although the functional importance of PPO in plants remains uncertain, a putative antipathogen role for walnut (Juglans regia) PPO was posited as early as 1911. However, despite the rich diversity of phenolics present in walnut leaves and hulls, walnut PPO has been little studied since the early 1900s. We cloned a PPO-encoding gene from a walnut pistillate flower cDNA library and designated the gene jrPPO1. Genomic Southern analysis demonstrated that jrPPO1 is the sole PPO gene in walnut. Transgenic tobacco (Nicotiana tabacum) plants expressing jrPPO1 display greater than 10-fold increases in leaf PPO activity compared with wild-type tobacco, demonstrating that jrPPO1 encodes a functional enzyme. The jrPPO1 protein is expressed primarily in the leaves, hulls, and flowers of walnut trees and is not regulated by wounding or methyl jasmonate. To examine whether walnut PPO could affect pathogen resistance, tobacco plants expressing jrPPO1 were challenged with Pseudomonas syringae pv. tabaci. Based on both symptom development and quantitative analyses of bacterial growth in planta, the PPO-expressing plants did not display increased resistance to this pathogen. Leaf extract browning assays indicated that tobacco leaves lack the endogenous phenolic substrates required for significant jrPPO1 activity and quinone production in planta.
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Holderbaum, Daniel Ferreira, Tomoyuki Kon, Tsuyoshi Kudo, and Miguel Pedro Guerra. "Enzymatic Browning, Polyphenol Oxidase Activity, and Polyphenols in Four Apple Cultivars: Dynamics during Fruit Development." HortScience 45, no. 8 (August 2010): 1150–54. http://dx.doi.org/10.21273/hortsci.45.8.1150.
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Enzymatic browning is one of the most important reactions that occur in fruits and vegetables, usually resulting in negative effects on color, taste, flavor, and nutritional value. The reaction is a consequence of phenolic compounds' oxidation by polyphenol oxidase (PPO), which triggers the generation of dark pigments. This is particularly relevant for apples, which are rich in polyphenols and highly susceptible to enzymatic browning. The objective of the present work was to quantify enzymatic browning and PPO activity and identify and quantify target polyphenols in apple [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] pulp in the cultivars (cvs.) Aori27, Elstar, Fuji, and Mellow at three fruit developmental stages (FDS). The enzymatic browning was quantified by tristimulus colorimetry; PPO activity was quantified by an enzyme–substrate spectrophotometric assay; phenolic compounds were determined and quantified by reverse-phase high-performance liquid chromatography–ultraviolet/visible–mass spectrometry. Enzymatic browning showed significant difference among cvs. and FDSs and interaction between both factors. PPO activity showed significant difference among cultivars and FDSs. A significant difference was evidenced for polyphenol content among cultivars and FDSs with interaction between both factors. Chlorogenic acid was the major phenolic compound in ‘Aori27’ and ‘Mellow’. In ‘Fuji’, chlorogenic acid and (–)-epicatechin were the major phenolics and in ‘Elstar’ (–)-epicatechin and procyanidin B2 were the major phenolics at different FDSs. The enzymatic browning showed high correlation to polyphenol content in all cultivars and high correlation was observed between browning and PPO activity in ‘Aori27’ and ‘Elstar’. The magnitude of the correlation between browning and polyphenols and PPO activity is genotype-specific. At the commercial harvest, ‘Fuji’ showed the highest polyphenol content and ‘Aori27’ showed the lowest level for enzymatic browning. Chemical names used: 3-(3,4-dihydroxycinnamoyl) quinic acid (chlorogenic acid), (–)-cis-3,3′,4′,5,7-pentahydroxyflavane (epicatechin), and cis,cis″-4,8″-Bi(3,3′,4′,5,7-pentahydroxyflavane) (procyanidin B2).
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Lee, Jo-Won, Sohee Yoon, Y. Martin Lo, Haohao Wu, Sook-Young Lee, and BoKyung Moon. "Intrinsic polyphenol oxidase-like activity of gold@platinum nanoparticles." RSC Advances 5, no. 78 (2015): 63757–64. http://dx.doi.org/10.1039/c5ra07636f.
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Au@Pt NPs showed PPO mimetic activity over a wider range of pH and temperatures compared to PPO. In the oxidation of all substrates, Au@Pt NPs exhibited higher affinity to the substrates, especially to catechol and pyrogallol, compared with PPO.
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Okpuzor, J., and O. Omidiji. "Peroxidase-Polyphenol Oxidase Association in Dioscorea esculenta." Zeitschrift für Naturforschung C 53, no. 11-12 (December 1, 1998): 957–60. http://dx.doi.org/10.1515/znc-1998-11-1204.
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Abstract A crude enzyme extract from Dioscorea esculenta var. fasiculata tissue subjected to ion exchange chromatography on DEAE-Sephadex A-50 column. This proced ure resolved the extract into two main protein peaks one of which eluted through the column relatively unbound while the other protein peak which remained bound to the column was eluted with 1.0 ᴍ NaCl. Both protein peaks contained polyphenol oxidase (PPO) and peroxidase (POD) activities. The non-binding protein peak was resolved by gel filtration on Sephadex G-200 into distinct PPO and POD activities and by virtue of their apparent molecular weights of 95.5 Kd and 38.0 Kd for PPO and POD respectively were determined to be the typical enzymes. The PPO activity was completely inhibited invitro by 5 mᴍ polyvinyl pyrrolidone (PVP). The binding protein peak was not resolved by gel filtration. It contained PPO activity which was not inhibited by PVP and a POD activity which was completely inhibited by dithiothreitol (DTT) This ionic protein peak contained 60% of total POD in the tissue, has an apparent molecular weight of 56 Kd and is suggested to be a strongly anionic peroxidase which also exhibits polyphenol oxidase activity.
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Mccaig, T. N., D. Y. K. Fenn, R. E. Knox, R. M. Depauw, J. M. Clarke, and J. G. Mcleod. "Measuring polyphenol oxidase activity in a wheat breeding program." Canadian Journal of Plant Science 79, no. 4 (October 1, 1999): 507–14. http://dx.doi.org/10.4141/p98-135.
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High levels of polyphenol oxidase (PPO) have been associated with discoloration of end-use products of wheat, especially certain noodle types. Two whole-seed methods of measuring PPO, one based on 10 mM tyrosine as substrate and the other on 90 mM catechol, were examined and modified to determine their potential as screening tools in large-scale breeding programs. Thirteen spring wheat and two spring triticale genotypes were used to compare the methods. Both methods could measure PPO on individual seeds. All genotypes displayed large seed-to-seed variation for PPO with both substrates. The mean coefficient of variation for the PPO values of individual seeds within genotypes was 39% with tyrosine and 34% with catechol. Furthermore, the PPO values of individual seeds within genotypes were not normally distributed for most genotypes. Identifying genotypes with incremental improvements in PPO would probably require measurement of 70–100 seeds. Approximately 50% of the catecholase activity was associated with the water extract after soaking seeds for 16 h, while all of the tyrosinase activity was still associated with the seed, suggesting that different enzymes are responsible for oxidizing tyrosine and catechol in wheat. While the 10 mM tyrosine assay was nondestructive and allowed plants to be generated from seeds low in PPO, 90 mM catechol reduced germination to less than 20%. Reducing the catechol to 30 mM improved germination to 85%, did not substrate-limit the reaction, and reduced the health risk associated with the assay. Spectral and kinetic differences between the assays were also considered. Key words: Triticum sp., wheat, polyphenol oxidase, catechol, tyrosine
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Toro-Uribe, Said, Jhair Godoy-Chivatá, Arley René Villamizar-Jaimes, María de Jesús Perea-Flores, and Luis J. López-Giraldo. "Insight of Polyphenol Oxidase Enzyme Inhibition and Total Polyphenol Recovery from Cocoa Beans." Antioxidants 9, no. 6 (May 27, 2020): 458. http://dx.doi.org/10.3390/antiox9060458.
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A full factorial design (ascorbic acid/l-cysteine inhibitors, temperature, and time as factors) study was conducted to enhance inhibition of polyphenol oxidase (PPO) activity without decreasing cocoa polyphenol concentrations. The data obtained were modelled through a new equation, represented by Γ, which correlates both high polyphenol content with reduced specific PPO activity. At optimized values (70 mM inhibitory solution at 96 °C for 6.4 min, Γ = 11.6), 93.3% PPO inhibition and total polyphenol of 94.9 mg GAE/g were obtained. In addition, microscopy images confirmed the cell morphological changes measured as the fractal dimension and explained the possible cell lysis and denaturation as a result of heat treatment and chemical inhibitors. Results also showed that PPO enzyme was most suitable (higher vmax/Km ratio) for catechol, with a reduction in its affinity of 13.7-fold after the inhibition heat treatment. Overall, this work proposed a suitable and food-safe procedure for obtaining enriched polyphenol extract with low enzyme activity.
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E, Kale, and Yuzugullu Karakus Y. "Application of Aqueous Two-Phase System to the Purification of Persimmon Polyphenol Oxidase." Open Access Journal of Microbiology & Biotechnology 7, no. 3 (July 4, 2022): 1–7. http://dx.doi.org/10.23880/oajmb-16000232.
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Polyphenol oxidases (PPOs), which have recently become very popular among many researchers, catalyze the oxidation of phenolic compounds. Polyphenol oxidases are generally found in plants. Among them, persimmon (Diospyros kaki L.) is known as a good source for polyphenol oxidases. In this study, the polyphenol oxidase enzyme was purified from persimmon fruit using aqueous two-phase (ATPS). The optimized system was composed of 18% (w/w) PEG4000, 7% (w/w) NaH2 P04 and 1% (w/w) NaCl (pH 8.5, 25°C and 5 g). The PPO enzyme was obtained from the system by 4.8-fold purification with 191% activity recovery. The molecular weight of the enzyme, 28 kDa, was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. In summary, it has been shown that the PPO enzyme can be obtained from persimmon in a short time and at low cost using a non-chromatographic method-ATPS.
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Rathjen, H., and SP Robinson. "Characterisation of a Variegated Grapevine Mutant Showing Reduced Polyphenol Oxidase Activity." Functional Plant Biology 19, no. 1 (1992): 43. http://dx.doi.org/10.1071/pp9920043.
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Fruit of the variegated grapevine mutant Bruce's Sport is known to dry to a lighter colour than other seedless varieties. The biochemical basis for this decreased browning capacity was investigated. Bruce's Sport grapes had similar levels of phenolic compounds to Sultana H5. Activity of the enzyme polyphenol oxidase (PPO EC 1.10.3.1) in mature berries of Bruce's Sport was only 20-30% of that in Sultana H5. No evidence of inhibitors or activators of PPO was found when berry extracts were mixed. PPO activity on a fresh weight basis was highest in the grape seed traces, intermediate in the skin, and lowest in the pulp in both varieties. In each tissue type, however, PPO activity in Bruce's Sport was less than 25% of that in Sultana H5. On a fresh weight basis, PPO activity in Sultana H5 berries was high at fruit set then declined as the berry developed. PPO activity per berry increased from fruit set until veraison, then remained constant. PPO activity showed similar changes during development of Bruce's Sport berries but was lower than in Sultana H5 at all stages. The Bruce's Sport grapes were variegated and the green regions of skin had similar PPO activity to Sultana H5 skin while the white regions had very low activity. Only the green regions of skin of Bruce's Sport grapes stained for PPO activity with endogenous or exogenously applied phenolic substrates. The decreased browning in this grapevine mutant apparently results from decreased levels of PPO activity in the white regions of the berry, possibly arising from a disruption in chloroplast development.
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Demir, D., C. Eken, E. Çelik, and N. Alkan. "Effect of Rhizoctonia spp. on Polyphenol Oxidase Enzyme Activity in Alfalfa Seedling." Research Journal of Biotechnology 16, no. 11 (October 25, 2021): 47–50. http://dx.doi.org/10.25303/1611rjbt4750.
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Soil borne diseases cause significant losses on quantity and quality of many crop species annually. Rhizoctonia is a widespread and ecologically diverse soilborne fungus causing different types of diseases in many plant species including alfalfa (Medicago sativa). Rhizoctonia species have been traditionally identified based on the cell nuclear condition. Polyphenol oxidases (PPOs) are ubiquitous copper-containing enzymes that are widely occurring enzymes among plants. PPOs are involved in the oxidation of polyphenols into quinones (antimicrobial compounds) and lignification of plant cells that contribute to the formation of defense barriers against pathogens. The study was conducted with the aim to determine the effect of indigenous isolates of a multinucleate (Rhizoctonia solani AG-4) and nineteen isolates of binucleate Rhizoctonia on PPO activity in alfalfa (cv. Gea) seedling under in vitro conditions. The activity of PPO enzyme was determined in inoculated and uninoculated control alfalfa plants after ten days from inoculation. There was a significant increase in the activity of PPO after treatment of alfalfa seedling with isolates of Rhizoctonia. Among Rhizoctonia isolates, highest induction of PPO activity was recorded with pathogenic R. solani AG-4. In present study, increased amounts of PPO were also observed in plants that were challenged with Rhizoctonia spp. PPO has a role in catalyzing phenolic oxidation in limiting disease development. PPO may therefore be involved in induction of defense resistance against plant diseases.
Dissertations / Theses on the topic "Polyphenol oxidase activity (PPO)"
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Stojanovic, Jelena. "Determination of polyphenol oxidase (PPO) activity, anthocyanin contents and the phytonutrient changes in blueberry juice as influenced by different processing methods." Diss., Mississippi State : Mississippi State University, 2008. http://library.msstate.edu/etd/show.asp?etd=etd-05292008-172900.
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Sadeque, Abdus. "Genetic mapping of noodle quality characters and rust resistance in hexaploid wheat." Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/3795.
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Polyphenol oxidase (PPO) catalyses undesirable darkening in wheat products such as Asian noodles. Genetic variation for PPO activity is characterized in bread wheat. Australian wheat breeding programmes recognize that reduced PPO activity is an important quality target. Despite this interest from breeders, no varieties possessing extremely low and null PPO activity exist. The development of null PPO wheat varieties is dependant on an understanding of the genetic control of the null phenotype. Knowledge of these factors will accelerate efforts to develop them. The inheritance of PPO activity was investigated in two populations that were derived from hybrids between a null PPO genotype and Australian wheat varieties Lang and QAlBis. Observed genetic ratios were consistent with two and three gene control, respectively in these populations. QTL mapping was performed in the QALBis x VAW08-A17 population. The Diversity Array Technology (DArT) approach was employed to genotype the QALBis x VAW08-A17 population. Three highly significant QTLs that control PPO activity were identified on chromosomes 2AL, 2BS and 2DL. Close associations between PPO activity and DArT marker loci wPt-7024, wPt-0094 and wPt-2544 were observed, respectively. Collectively, these loci explained 74% of the observed variation in PPO activity across seasons. Significant QTLs on chromosomes 1B and 3B were also identified that together explained an additional 17% of variation in PPO activity. The relationship between PPO activity and yellow alkaline noodles (YAN) colour stability parameters was investigated in a DM5637*B8 x H45 doubled haploid population. PPO activity and changes in YAN brightness (ΔL* 0-24h) and yellowness (Δb* 0-24h) in both seasons were analysed. Quantitative trait analyses of PPO activity, flour yellowness (b*) and YAN colour stability was also conducted in this population. QTL mapping of variation in PPO activity in the DM5637*B8 x H45 DH population identified a highly significant QTL on chromosome 2AL, which explained 52% of the observed variation across seasons. Regression analysis identified that wPt-7024 was highly significantly associated with PPO activity in this population. A highly significant association between this marker and PPO was also identified in the QALBis x VAW08-A17 population. Collectively, the three identified QTLs (on chromosomes 2AL, 7A and 7B) explained 71% of variation in PPO activity across seasons. A highly significant (P<0.001) QTL on chromosome 2B along with significant (P<0.01) QTLs on the chromosomes 1A, 3B, 4B and 5B were found to control flour yellowness. The QTLs on 2B, 4B and 5B were detected in both seasons analysed and accounted for 90% of variation in flour b* across seasons. The study on YAN colour stability located two highly significant (P<0.001) QTLs and two significant (P<0.01) QTLs that controlled the change in brightness of yellow alkaline noodle. The 2A QTL accounted for 64% of observed variation across seasons. It was in the same location as the PPO QTL and shared a common closest marker wPt-7024. Only one significant QTL for YAN a* (0-24h) was identified. It accounted for 12% of variation across seasons and was only detected in one season. One highly significant (P<0.001) QTL and two significant (P<0.01) QTLs were identified that controlled the change in yellowness of yellow alkaline noodle. The 2A QTL accounted for 68% of observed variation across seasons. The location of this QTL corresponded with that of 2A QTLs for PPO activity and L* of YAN in this study. Furthermore, wPt-7024 was also identified as the marker with the most significant association with L*. The identification of a correlation between the characters and a common location of a highly significant QTL for each of these characters indicates that it is likely that PPO activity is directly responsible for a large proportion of the changes in brightness and yellowness of YAN. QTLs for L* and b* of YAN were detected in a common location on chromosome 1A. However, no corresponding QTL was identified that controls PPO activity, highlighting the complexity of the relationship between these traits. Resistance to three rust pathogens (Puccinia graminis, Puccinia striiformis, and Puccinia triticina) was also investigated in the DM5637*B8 x H45 DH population because they are major yield limiting diseases in wheat. Disease response data at the seedling stage were converted to genotypic scores for rust genes Sr24/Lr24, Sr36, Lr13 and Yr7 to construct a genetic linkage map. No recombination was observed between rust resistance genes Sr36, Lr13 and Yr7 in this DH population. Therefore, these genes mapped in the same position on chromosome 2B. The Lr24/Sr24 locus was incorporated into the chromosome 3D map. Interval mapping analysis identified QTLs on chromosomes 2B, 3B, 4B and 5B that control adult plant resistance (APR) to stripe rust. Two QTLs on chromosomes 2B and 3D were identified that controlled APR to leaf rust in this DH population.
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Sadeque, Abdus. "Genetic mapping of noodle quality characters and rust resistance in hexaploid wheat." University of Sydney, 2008. http://hdl.handle.net/2123/3795.
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Doctor of PhilosophyPolyphenol oxidase (PPO) catalyses undesirable darkening in wheat products such as Asian noodles. Genetic variation for PPO activity is characterized in bread wheat. Australian wheat breeding programmes recognize that reduced PPO activity is an important quality target. Despite this interest from breeders, no varieties possessing extremely low and null PPO activity exist. The development of null PPO wheat varieties is dependant on an understanding of the genetic control of the null phenotype. Knowledge of these factors will accelerate efforts to develop them. The inheritance of PPO activity was investigated in two populations that were derived from hybrids between a null PPO genotype and Australian wheat varieties Lang and QAlBis. Observed genetic ratios were consistent with two and three gene control, respectively in these populations. QTL mapping was performed in the QALBis x VAW08-A17 population. The Diversity Array Technology (DArT) approach was employed to genotype the QALBis x VAW08-A17 population. Three highly significant QTLs that control PPO activity were identified on chromosomes 2AL, 2BS and 2DL. Close associations between PPO activity and DArT marker loci wPt-7024, wPt-0094 and wPt-2544 were observed, respectively. Collectively, these loci explained 74% of the observed variation in PPO activity across seasons. Significant QTLs on chromosomes 1B and 3B were also identified that together explained an additional 17% of variation in PPO activity. The relationship between PPO activity and yellow alkaline noodles (YAN) colour stability parameters was investigated in a DM5637*B8 x H45 doubled haploid population. PPO activity and changes in YAN brightness (ΔL* 0-24h) and yellowness (Δb* 0-24h) in both seasons were analysed. Quantitative trait analyses of PPO activity, flour yellowness (b*) and YAN colour stability was also conducted in this population. QTL mapping of variation in PPO activity in the DM5637*B8 x H45 DH population identified a highly significant QTL on chromosome 2AL, which explained 52% of the observed variation across seasons. Regression analysis identified that wPt-7024 was highly significantly associated with PPO activity in this population. A highly significant association between this marker and PPO was also identified in the QALBis x VAW08-A17 population. Collectively, the three identified QTLs (on chromosomes 2AL, 7A and 7B) explained 71% of variation in PPO activity across seasons. A highly significant (P<0.001) QTL on chromosome 2B along with significant (P<0.01) QTLs on the chromosomes 1A, 3B, 4B and 5B were found to control flour yellowness. The QTLs on 2B, 4B and 5B were detected in both seasons analysed and accounted for 90% of variation in flour b* across seasons. The study on YAN colour stability located two highly significant (P<0.001) QTLs and two significant (P<0.01) QTLs that controlled the change in brightness of yellow alkaline noodle. The 2A QTL accounted for 64% of observed variation across seasons. It was in the same location as the PPO QTL and shared a common closest marker wPt-7024. Only one significant QTL for YAN a* (0-24h) was identified. It accounted for 12% of variation across seasons and was only detected in one season. One highly significant (P<0.001) QTL and two significant (P<0.01) QTLs were identified that controlled the change in yellowness of yellow alkaline noodle. The 2A QTL accounted for 68% of observed variation across seasons. The location of this QTL corresponded with that of 2A QTLs for PPO activity and L* of YAN in this study. Furthermore, wPt-7024 was also identified as the marker with the most significant association with L*. The identification of a correlation between the characters and a common location of a highly significant QTL for each of these characters indicates that it is likely that PPO activity is directly responsible for a large proportion of the changes in brightness and yellowness of YAN. QTLs for L* and b* of YAN were detected in a common location on chromosome 1A. However, no corresponding QTL was identified that controls PPO activity, highlighting the complexity of the relationship between these traits. Resistance to three rust pathogens (Puccinia graminis, Puccinia striiformis, and Puccinia triticina) was also investigated in the DM5637*B8 x H45 DH population because they are major yield limiting diseases in wheat. Disease response data at the seedling stage were converted to genotypic scores for rust genes Sr24/Lr24, Sr36, Lr13 and Yr7 to construct a genetic linkage map. No recombination was observed between rust resistance genes Sr36, Lr13 and Yr7 in this DH population. Therefore, these genes mapped in the same position on chromosome 2B. The Lr24/Sr24 locus was incorporated into the chromosome 3D map. Interval mapping analysis identified QTLs on chromosomes 2B, 3B, 4B and 5B that control adult plant resistance (APR) to stripe rust. Two QTLs on chromosomes 2B and 3D were identified that controlled APR to leaf rust in this DH population.
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Ferreira, Elys Raquel Andrade. "Filmes de polipirrol como matrizes para a imobilização da polifenol oxidase e aplicação como biossensores amperométricos na análise de compostos fenólicos." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-01122014-112608/.
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Nesta dissertação, a polifenol oxidase (PFO) como extrato bruto de abacate (Persea americana) foi imobilizada em filmes de polipirrol (PPI) sintetizados eletroquimicamente utilizando o glutaraldeído (GA) como um agente de ligação entrecruzada. Os filmes PPI e PPI/PFO-GA foram caracterizados por eletroquímica, principalmente voltametria cíclica, sendo avaliadas a eletroatividade e a reversibilidade eletroquímica. A detecção de compostos fenólicos em soluções padrão foi feita por cronoamperometria, tendo um controle sobre a concentração dos compostos. O processo de transferência de massa foi monitorado com uma microbalança de cristal de quartzo eletroquímica. Os resultados indicaram uma boa reprodutibilidade das medidas na detecção dos compostos fenólicos. A estabilidade do biossensor em uma solução tampão manteve-se durante 27 dias, um resultado aceitável já que é encontrado na literatura um tempo de vida estável para sistemas semelhantes em tomo de 30 diasIn this dissertation, polyphenol oxidase (PPO) as crude extract of avocado (Persea americana) was immobilized on electrochemical1y synthesized polypyrrole (PPY) films using glutaraldehyde (GA) as a crosslinking agent. PPY and PPY/PPO-GA films were electrochemical1y characterized, mainly by cyclic voltametry, where electroactivity and electrochemical reversibility were evaluated. The detection of phenolic compounds in standard samples was made by chronoamperometry with a control over the compound concentration. The process of mass transfer was monitored with an electrochemical quartz crystal microbalance (EQCM). Our results indicated a good repeatability of the measurements for the detection of phenolic compounds. The stability of biosensor in a buffer solution has remained for 27 days, a result acceptable since it is found in the literature a time of life stable for similar systems around 30 days
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Falguera, Pascual Víctor. "Polyphenol oxidase: Activity, properties of its products and inactivation by innovative technologies." Doctoral thesis, Universitat de Lleida, 2012. http://hdl.handle.net/10803/107819.
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Polyphenol oxidase (PPO) affects both kinds of matters that are nowadays at the forefront of the quality concept: those aspects related to health and those regarding organoleptic perception of food. In this Thesis, PPO activity has been characterized in different fruits and situations, and mathematical models to describe melanin formation from monophenolic and o diphenolic substrates have been developed. In addition, potential toxicity of these melanins on the pancreatic proteases carboxypeptidase A, carboxypeptidase B and trypsin has been studied. The second part of the Thesis covers PPO inactivation by innovative technologies, and the side effects that they cause on different parameters. Ultraviolet-visible irradiation has been modeled, and PPO inactivation by this method has been assessed in model solutions and in apple, pear and grape juices. Moreover, the effects of must irradiation on the quality of wine have also been assessed. In addition, high-hydrostatic pressure effectiveness in inactivating apple PPO was tested, as well as its effects on juices color.La polifenol oxidasa (PPO) afecta a ambdós tipus de qüestions que són actualment al capdavant del concepte de qualitat: els aspectes relacionats amb la salut i els relatius a la percepció organolèptica dels aliments. En aquesta Tesi, l'activitat de la PPO s'ha caracteritzat en diferents fruites i situacions, i s'han desenvolupat models matemàtics per descriure la formació de melanina a partir de substrats monofenòlics i o difenòlics. A més, s'ha estudiat la toxicitat potencial d'aquestes melanines sobre les proteases pancreàtiques carboxipeptidasa A, carboxipeptidasa B i tripsina. La segona part de la Tesi tracta la inactivació de la PPO per tecnologies innovadores, i els efectes secundaris que causen en diferents paràmetres. La irradiació ultraviolada-visible ha estat modelitzada, i la inactivació de la PPO per aquest mètode s'ha avaluat en solucions model i en sucs de poma, pera i raïm. A més, els efectes de la irradiació del most sobre la qualitat del vi també han estat avaluats. En darrer lloc, s'estudià l'eficàcia de l'alta pressió hidrostàtica en la inactivació de la PPO de poma, així com els seus efectes sobre el color dels sucs.
La polifenol oxidasa (PPO) afecta a ambos tipos de cuestiones que se encuentran actualmente al frente del concepto de calidad: los aspectos relacionados con la salud y los relativos a la percepción organoléptica de los alimentos. En esta Tesis, la actividad de la PPO se ha caracterizado en diferentes frutas y situaciones, y se han desarrollado modelos matemáticos para describir la formación de melanina a partir de sustratos monofenólicos y o difenólicos. Además, se ha estudiado la toxicidad potencial de estas melaninas sobre las proteasas pancreáticas carboxipeptidasa A, carboxipeptidasa B y tripsina. La segunda parte de la Tesis trata la inactivación de la PPO por tecnologías innovadoras, y los efectos secundarios que causan en diferentes parámetros. La irradiación ultravioleta-visible ha sido modelizada, y la inactivación de la PPO por este método se ha evaluado en soluciones modelo y en zumos de manzana, pera y uva. Además, los efectos de la irradiación del mosto sobre la calidad del vino también han sido evaluados. Por último, se estudió la eficacia de la alta presión hidrostática en la inactivación de la PPO de manzana, así como sus efectos sobre el color de los zumos.
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Barioto, Valquiria da Cruz Rodrigues. "Influência do contra-íon usado na eletrossíntese do polipirrol em sua resposta como biossensor eletroquímico após a imobilização da polifenol oxidase." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-24092009-144106/.
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Neste trabalho, foram fabricados biossensores amperométricos a partir do uso da polifenol oxidase (PFO), obtida do abacate como fonte enzimática, imobilizada em filmes de polipirrol (PPI) e que foram eletrossintetizados em meio de três diferentes eletrólitos de suporte (NaCl e NaClO4 e NaDDS). O método de imobilização enzimática foi o da adsorção, sendo a solução de enzima adicionada à solução com o pirrol e o eletrólito durante o processo de eletropolimerização. Os filmes de PPI/PFO foram caracterizados por técnicas eletroquímicas, principalmente por voltametria cíclica. A detecção de compostos fenólicos (catecol e pirogalol) foi realizada pela técnica de cronoamperometria após se variar a concentração do analito. A morfologia dos filmes foi estudada por microscopia de força atômica (AFM), sendo observado que a presença da enzima no filme polimérico assim como o uso de diferentes eletrólitos de suporte levou a diferenças na superfície dos filmes. Além disto, verificou-se que o biossensor construído a partir do uso do NaCl, apresentava uma resposta mais eficiente, ou seja, ele foi capaz de detectar catecol e pirogalol em um menor limite de detecção.In this study amperometric biosensors were manufactured from the use of polyphenol oxidase (PPO) obtained from avocado as a source of enzyme immobilized in polypyrrole (PPY) films that were electrosynthesized with three different support electrolytes (NaCl, NaClO4 and NaDDS). The method of enzyme immobilization was the adsorption. The PPO was added in the solution containing pyrrole and electrolyte during electropolymerization. The PPY/PPO films were characterized by electrochemical techniques mainly by cyclic voltammetry. Detection of phenolic compounds (catechol and pyrogallol) was performed by the technique of chronoamperometry after varying the concentration of the analyte. The morphology of the films was studied by the atomic force microscopy (AFM) and observed that the presence of the enzyme in the polymer film and the use of different electrolytes support led to differences in the surface of films. However it was found that the biosensor constructed from the use of NaCl showed more efficient response and it was able to detect catechol and pyrogallol in a lower limit of detection.
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Hossain, Abzal. "Inhibition of tyrosinase activity by metallothionein from Aspergillus niger." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0015/MQ55068.pdf.
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Vázquez, Daniel. "Effects of genotype and environment on polyphenol oxidase activity and related properties of red and white wheats." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0021/MQ56149.pdf.
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WANG, GAI. "Effect of Frozen Storage on Antioxidant Capacity, Polyphenol Oxidase Activity, and Phenolic and Flavonoid Content and Color of Pawpaw Pulp." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1373373703.
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Miladinović, Zoran. "Kinetics of destruction of potato polyphenol oxidase (PPO) during vacuum microwave blanching." Thesis, 2006. http://hdl.handle.net/2429/17575.
Full textAbstract:
Vacuum microwave (VM) blanching decreases enzymatic food browning at
low temperatures (between ~40-55°C) when compared to conventional processing
methods. The impact and reaction of microwave blanching on polyphenol oxidase
(PPO) of the Russet potato was investigated and compared with the effects of
conventional convective heating. In order to closely examine PPO kinetics in a
microwave field and to establish a PPO assay for use in further investigations,
potato puree plus polyvinylpolypyrrolidone (PVPP) was centrifuged and filtered to
produce a treatment ready suspension. Whole potatoes were cut into French fry
strips and blanched using a pilot-sized V M dehydrator. This was compared to a
steam kettle blanch to determine the blanch effects on physical form. Finally, two
different microwave treatments were utilized along with a heated water bath in order
to compare the microwave heated potato suspension samples with conventional
heating. Microwave treatments used a 700 W, 2450 MHz vacuum microwave oven
and an Ethos Synth (ES-MR) microwave reactor set at 2450 MHz, which dropped
the microwave power level from 700 W to below 100 W after reaching the desired
temperature. Experiments in all three treatments were conducted under controlled
temperatures between 40°C and 70°C. The decimal reduction values (D-value) of
PPO were reduced by heating in vacuum microwave treatments as compared to
heating in a water bath at temperatures between 40°C and 57°C. At these
temperatures, the D-values, z-values and activation energies (E[sub a]) for the PPO model reaction were significantly lower (p < 0.05) for the VM and the ES than the heated
water bath. The results suggest the existence of an alternative inactivation
mechanism for PPO when heated in a microwave field compared to a water bath at
low processing temperatures.Land and Food Systems, Faculty of
Graduate
Books on the topic "Polyphenol oxidase activity (PPO)"
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Patel, Usha R. Polyphenol oxidase activity assay based on fibre optics. Manchester: UMIST, 1997.
Find full textBook chapters on the topic "Polyphenol oxidase activity (PPO)"
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Jukanti, Aravind. "Advances in Polyphenol Oxidase (PPO) Research." In Polyphenol Oxidases (PPOs) in Plants, 107–31. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-5747-2_7.
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Wakayama, T. "Polyphenol Oxidase Activity in Japanese Apples." In ACS Symposium Series, 251–66. Washington, DC: American Chemical Society, 1995. http://dx.doi.org/10.1021/bk-1995-0600.ch020.
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Flurkey, William H., and Janis Ingebrigtsen. "Polyphenol Oxidase Activity and Enzymatic Browning in Mushrooms." In ACS Symposium Series, 44–54. Washington, DC: American Chemical Society, 1989. http://dx.doi.org/10.1021/bk-1989-0405.ch004.
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Osuga, D., A. Van Der Schaaf, and J. R. Whitaker. "Control of polyphenol oxidase activity using a catalytic mechanism." In Protein Structure-Function Relationships in Foods, 62–88. Boston, MA: Springer US, 1994. http://dx.doi.org/10.1007/978-1-4615-2670-4_4.
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Rodney, Rebecca L., and Alan J. Russell. "Enzyme Chemistry in Carbon Dioxide." In Green Chemistry Using Liquid and Supercritical Carbon Dioxide. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780195154832.003.0010.
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Enzymes are biocatalysts constructed of a folded chain of amino acids. They may be used under mild conditions for specific and selective reactions. While many enzymes have been found to be catalytically active in both aqueous and organic solutions, it was not until quite recently that enzymes were used to catalyze reactions in carbon dioxide when Randolph et al. (1985) performed the enzyme-catalyzed hydrolysis of disodium p-nitrophenol using alkaline phosphatase and Hammond et al. (1985) used polyphenol oxidase to catalyze the oxidation of p-cresol and p-chlorophenol. Since that time, more than 80 papers have been published concerning reactions in this medium. Enzymes can be 10–15 times more active in carbon dioxide than in organic solvents (Mori and Okahata, 1998). Reactions include hydrolysis, esterification, transesterification, and oxidation. Reactor configurations for these reactions were batch, semibatch, and continuous. There are many factors that influence the outcome of enzymatic reactions in carbon dioxide. These include enzyme activity, enzyme stability, temperature, pH, pressure, diffusional limitations of a two-phase heterogeneous mixture, solubility of enzyme and/or substrates, water content of the reaction system, and flow rate of carbon dioxide (continuous and semibatch reactions). It is important to understand the aspects that control and limit biocatalysis in carbon dioxide if one wants to improve upon the process. This chapter serves as a brief introduction to enzyme chemistry in carbon dioxide. The advantages and disadvantages of running reactions in this medium, as well as the factors that influence reactions, are all presented. Many of the reactions studied in this area are summarized in a manner that is easy to read and referenced in Table 6.1. Carbon dioxide is cited as a good choice of solvents for a number of reasons. Some of the advantages of running reactions in carbon dioxide instead of the more traditional organic solvents include the low viscosity of the solvent, the convenient recovery of the products and non-reacted components, abundant availability, low cost, no solvent contamination of products, full miscibility with other gases, non-existent toxicity, low surface tension, non-flammability, and recyclability. The low mass-transfer limitations are an advantage because of the large diffusivity of reactants.
Conference papers on the topic "Polyphenol oxidase activity (PPO)"
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Hong-jia, Lin, Li Lin, Wang Wen-zong, Chen Ling, and Li Bing. "Effect of ultrasound in combination with food additives on polyphenol oxidase activity." In 2011 International Conference on Human Health and Biomedical Engineering (HHBE). IEEE, 2011. http://dx.doi.org/10.1109/hhbe.2011.6029004.
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Popovici, Ana, Nicolae Bujoreanu, and Valentina Svetlicenco. "Modificarea activității peroxidazei și a polifenoloxidazei în fructele de prun în funcție de influența SBA Reglalg, microelementelor (B, Zn, Mn, Mo) și a metodelor de păstrare." In International Scientific Symposium "Plant Protection – Achievements and Prospects". Institute of Genetics, Physiology and Plant Protection, Republic of Moldova, 2020. http://dx.doi.org/10.53040/9789975347204.73.
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When storaging the plum fruits of the varieties Stenley under normal atmospheric conditions and by the method of treating them with the synthetic inhibitor of ethylene Fitomag, the modification of peroxidase and polyphenol oxidase activity in fruits depended on the conditions and duration of storage, metabolic processes course in fruit during storage, the particularities of the varieties and their storage methods. The gradual decrease in peroxidase activity and the increase in polyphenol oxidase activity occurred in the case of fruit preservation by both methods. In the fruits storaged by the Fitomag method, the values of these enzymes were lower compared to those in the ordinary atmosphere. The lower intensity of the redox processes has beneficially influenced the preservation of the quality of the fruits preserved by this method compared to the usual atmosphere. There were also essential differences between the control and the variants treated with SBA Reglalg and microelements, as well as between varieties.
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Popovici, Ana, and Nicolae Bujoreanu. "Activitatea enzimelor antioxidante la păr în funcție de acțiunea SBA Reglalg și a microelementelor." In International Scientific Symposium "Plant Protection – Achievements and Prospects". Institute of Genetics, Physiology and Plant Protection, Republic of Moldova, 2020. http://dx.doi.org/10.53040/9789975347204.72.
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According to the data obtained from the research we find that the natural growth regulator Reglalg and Reglalg in combination with trace elements have had a beneficial effect in regulating the activity of enzymes peroxidase and polyphenol oxidase which play an important role in vital processes of resistance and increased plant productivity.The redox processes in the leaves of the tardive Noiabriscaia and Socrovisce pear varieties depended on the metabolic processes in the development of plants in ontogenesis, the stages of plant development, the action of their living conditions, the amount of oxidative substances that formed in plant cells under the action of high temperatures, give the particularities of varieties as well as the action of SBA Reglalg and microelements used to treat trees.Thus, with the modification of peroxidase and polyphenol oxidase activity during phenophases, we find their participation in metabolic processes that correlate with the function of resistance and adaptation of plants to unfavorable environmental conditions and consequently crop formation and fruit quality.
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Barreto, Andres Felipe Moreno, Giuseppe Vignali, and Luca Sandei. "Effect of High Pressure Processing on enzymatic activity for strawberries, sour cherries and red grapes." In the 7th International Food Operations and Processing Simulation Workshop. CAL-TEK srl, 2021. http://dx.doi.org/10.46354/i3m.2021.foodops.004.
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Color degradation is an important factor that affect the quality and acceptability of fruit juices and purees; several enzymes, as well as the microbial endogenous population are not only responsible for this phenomenon but for changes in flavor and texture. Traditional stabilization methods have been used to preserve these kind of products; however, there is a negative impact on vitamins and bioactive compounds composition. High Pressure Processing (HPP) is a non-thermal alternative that has been applied for the extension of shelf life of fresh products, reducing the adverse effects of classical treatments. The aim of this review is to provide a scientific base on the effect of HPP technology in terms of enzymatic inactivation (peroxidase, polyphenol oxidase, ascorbate oxidase and β-glucosidase) in comparison with a conventional pasteurization process in strawberries, sour cherries and red grapes, and to propose an optimization strategy for the operational parameters to achieve the greatest inactivation
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Yakubovskaya, A. I., I. A. Kameneva, S. V. Didovich, I. I. Smirnova, N. A. Kashirina, and M. V. Ermolaeva. "Influence of microbial preparations on the enzymatic activity of Thymus vulgaris L." In CURRENT STATE, PROBLEMS AND PROSPECTS OF THE DEVELOPMENT OF AGRARIAN SCIENCE. Federal State Budget Scientific Institution “Research Institute of Agriculture of Crimea”, 2020. http://dx.doi.org/10.33952/2542-0720-2020-5-9-10-119.
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Recently, special concern has been shown to common thyme (Thymus vulgaris L.), essential oil of which has a valuable ingredients and is of interest for different uses. The purpose of the research was to study the influence of polyfunctional microbial preparations on the enzymatic activity of T. vulgaris, which is grown under conditions of the foothill zone of the Crimea. In field experiments on southern Chernozem, we studied the influence of “Biopolycid” and “Cyanobacterium consortium” preparations on the activity of catalase and polyphenol oxidase enzymes in leaves of T. vulgaris. The microbial preparations were spread onto the top layer of the soil once at the stem-extension stage. In this case, their use promoted efficient plant-microbial interaction, i.e. induction of antioxidant enzyme activity, increasing stress resistance of plants. Thus, in the foothills of the Crimea, according to the results of the first year of research, it was proved that top-soil dressing with polyfunctional microbial preparations “Biopolycid” and “Cyanobacterium consortium” increased the enzymatic activity of T. vulgaris plants
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"Polyphenol oxidase gene family in barley (Hordeum vulgare L.): structural organization and functional activity of the genes in respect to black grain pigment formation." In Plant Genetics, Genomics, Bioinformatics, and Biotechnology. Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 2019. http://dx.doi.org/10.18699/plantgen2019-104.
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Ferreira, Rui Manuel Alves, Isabel Maria Simão Alves-Pereira, Joana Manuela Capela-Pires, and Marta Sofia Garcia Candeias. "Functional and conservation value of fruits - a lab approach." In Sixth International Conference on Higher Education Advances. Valencia: Universitat Politècnica de València, 2020. http://dx.doi.org/10.4995/head20.2020.11082.
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Fruits are a relevant source of phenols and ascorbate, biomolecules which scavenge reactive oxygen species. For this reason, they are considered as healthy for the human being. Fruits quality depends on their levels of antioxidants and enzyme activities that ensure their conservation. The aim of this work was to plan and execute a laboratory class of Enzymology, a discipline of Biochemistry degree of University of Évora, Portugal, for determining the functional and conservation value of three different fruits types, sold in the market of Évora, Portugal. The development of this activity allowed that students of a pilot class participate in a laboratory activity which intended to compare the content of phenols, ascorbate, and polyphenol oxidase enzyme activity present in apple, peach and blueberries pulp. At Lab activity, the students successfully determined markers of functional and conservation value of selected fruits. The skills acquired by the students, in terms of obtaining fruit pulp and their composition in antioxidants, stimulated their commitment degree on the application of biochemistry in the everyday, acquiring thereby significant learning, with a high degree of satisfaction.
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Popovici, Ana, Valentina Svetlicenco, and Nicolae Bujoreanu. "Modificarea activiății peroxidazei și a polifenoloxidazei în fructele de prun în dependență de varianta de tratare în perioada de vegetație și metodele de păstrare aplicate." In VIIth International Scientific Conference “Genetics, Physiology and Plant Breeding”. Institute of Genetics, Physiology and Plant Protection, Republic of Moldova, 2021. http://dx.doi.org/10.53040/gppb7.2021.22.
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The plum fruits of the President variety were preserved by three methods. I- keeping fruits in the ordinary atmosphere (AO). II - the fruits before being stored for a long time in AO were treated with the synthetic inhibitor of ethylene Fitomag and III - the fruits were kept in a controlled atmosphere (CA). Du-ring the storage of the fruits of the respective variety, the activity of some antioxidant enzymes was de-termined by the mentioned methods. As a result, results were obtained regarding the modification of the activity of the enzymes peroxidase and polyphenol oxidase. Their activity changed depending on the me-tabolic processes that took place when the fruits maturation, as well as the conditions, duration and stora-ge methods. It also depended on the biological peculiarities of the variety and the influence of the sub-stances with which the plum trees were treated during the vegetation period. The highest activity of these enzymes was in the fruits kept in the usual atmosphere, then followed by their activity in the fruits kept with Fitomag and their lowest activity was in the fruits kept in CA. In the fruits preserved by the last two methods, the metabolic processes and those of oxide reduction went slower and the fruits were kept 10, 16 days longer than in AO. There were also significant differences in the activity of these enzymes, being higher in the variant treated with SBA Reglalg and microelements than in the control variant.
Reports on the topic "Polyphenol oxidase activity (PPO)"
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Steffens, John C., and Eithan Harel. Polyphenol Oxidases- Expression, Assembly and Function. United States Department of Agriculture, January 1995. http://dx.doi.org/10.32747/1995.7571358.bard.
Full textAbstract:
Polyphenol oxidases (PPOs) participate in the preparation of many plant products on the one hand and cause considerable losses during processing of plant products on the other hand. However, the physiological functions of plant PPO were still a subject of controversy at the onset of the project. Preliminary observations that suggested involvement of PPOs in resistance to herbivores and pathogens held great promise for application in agriculture but required elucidation of PPO's function if modulation of PPO expression is to be considered for improving plant protection or storage and processing of plant products. Suggestions on a possible role of PPO in various aspects of chloroplast metabolism were also relevant in this context. The characterization of plant PPO genes opened a way for achieving these goals. We reasoned that "understanding PPO targeting and routing, designing ways to manipulate its expression and assessing the effects of such modifications will enable determination of the true properties of the enzyme and open the way for controlling its activity". The objective of the project was to "obtain an insight into the function and biological significance of PPOs" by examining possible function(s) of PPO in photosynthesis and plant-pest interactions using transgenic tomato plants; extending our understanding of PPO routing and assembly and the mechanism of its thylakoid translocation; preparing recombinant PPOs for use in import studies, determination of the genuine properties of PPOs and understanding its assembly and determining the effect of PPO's absence on chloroplast performance. Results obtained during work on the project made it necessary to abandon some minor objectives and devote the effort to more promising topics. Such changes are mentioned in the 'Body of the report' which is arranged according to the objectives of the original proposal. The complex expression pattern of tomato PPO gene family was determined. Individual members of the family are differentially expressed in various parts of the plant and subjected to developmentally regulated turnover. Some members are differentially regulated also by pathogens, wounding and chemical wound signals. Wounding systemically induces PPO activity and level in potato. Only tissues that are developmentally competent to express PPO are capable of responding to the systemic wounding signal by increased accumulation of PPO mRNA. Down regulation of PPO genes causes hyper susceptibility to leaf pathogens in tomato while over expression regulation of PPO expression in tomato plants is their apparent increased tolerance to drought. Both the enhanced disease resistance conferred by PPO over expression and the increased stress tolerance due to down regulation can be used in the engineering of improved crop plants. Photosynthesis rate and variable fluorescence measurements in wild type, and PPO-null and over expressing transgenic tomato lines suggest that PPO does not enable plants to cope better with stressful high light intensities or reactive oxygen species. Rather high levels of the enzyme aggravate the damage caused under such conditions. Our work suggests that PPO's primary role is in defending plants against pathogens and herbivores. Jasmonate and ethylene, and apparently also salicylate, signals involved in responses to wounding and defense against herbivores and pathogens, enhance markedly and specifically the competence of chloroplasts to import and process pPPO. The interaction of the precursor with thylakoid membranes is primarily affected. The routing of PPO shows other unusual properties: stromal processing occurs in two sites, resulting in intermediates that are translocated across thylakoids by two different mechanisms - a DpH- and a Sec-dependent one. It is suggested that the dual pattern of processing and routing constitutes a'fail safe' mechanism, reflecting the need for a rapid and flexible response to defense challenges. Many of the observations described above should be taken into consideration when manipulation of PPO expression is contemplated for use in crop improvement.
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Steffens, John, Eithan Harel, and Alfred Mayer. Coding, Expression, Targeting, Import and Processing of Distinct Polyphenoloxidases in Tissues of Higher Plants. United States Department of Agriculture, November 1994. http://dx.doi.org/10.32747/1994.7613008.bard.
Full textAbstract:
Polyphenol oxidase (PPO) catalyzes the oxidation of phenols to quinones at the expense of O2. PPOs are ubiquitous in higer plants, and their role in oxidative browning of plant tissues causes large annual losses to food production. Despite the importance of PPOs to agriculture, the function(s) of PPOs in higher plants are not understood. Among other roles, PPOs have been proposed to participate in aspects of chloroplast metabolism, based on their occurrence in plastids and high Km for O2. Due to the ability of PPO to catalyze formation of highly reactive quinones, PPOs have also been proposed to be involved in a wide array of defensive interactions with insect, bacterial, and fungal pests. Physiological and biochemical studies of PPO have provided few answers to the major problems of PPO function, subcellular localization, and biochemical properties. This proposal achieved the following major objectives: cloning of PPO cDNAs in potato and tomato; characterization of the tomato PPO gene family; antisense downregulation of the tomato PPO gene family; and reduction in post-harvest enzymic browning of potato through expression of antisense PPO genes under the control of tuber-specific promoters. In addition, we established the lumenal localization of PPO, characterized and clarified the means by which PPOs are imported and processed by chloroplasts, and provided insight into the factors which control localization of PPOs. This proposal has thereby provided fundamental advances in the understanding of this enzyme and the control of its expression.