Academic literature on the topic 'Fields of Research – 290000 Engineering and Technology – 290100 Industrial Biotechnology and Food Sciences'

This thesis relates the physicochemical properties of phenolic compounds to their antioxidant activities. It focuses on the partitioning of phenolic compounds between hydrophilic and lipophilic environments and the relevance this has to their in vivo health effects. Data in the literature was lacking so the phase partition coefficients (log P) of 53 phenolic antioxidants were measured by reversed-phase HPLC and calculated by log P prediction software. There was a very strong linear correlation between measured and calculated values (r=0.91). The importance of log P in determining antioxidant assay values was then tested by developing an assay system capable of measuring activities of both hydrophilic and lipophilic antioxidants. This Lipid Peroxidation Inhibition Capacity Assay (LPIC), based on using liposomes to simulate a cell membrane environment, was then used to measure the activity of antioxidants with a broad range of structures. The activities were correlated against log p, the difference of heat of formation (∆Hf) and half-wave potential (Ep/2) and used to derive a predictive model to calculate the LPIC activity. There was a highly significant linear correlation between the calculated and measured values. The LPIC activities also correlated well to published LDL inhibition activities but not to measured ORAC activities. These findings suggested that behaviours of antioxidants in the small unilamellar vesicles of the LPIC assay were similar to that in the LDL assay but not to the aqueous phase based ORAC assay. The LPIC assay may therefore be a better indicator of potential health benefits of antioxidants in the human body than the ORAC assay. The possible mechanistic reasons are that it may better reflect ability to prevent the oxidation of LDL blood stream particles that leads to cardiovascular disease and also takes into account the importance of membrane solubility which can raise the cellular concentration and thus potential to protect cells from oxidative damage. KEYWORDS: LPIC, LDL; Antioxidant; Phytochemical; Polyphenolic; Phenolic acid; Flavonoids; log P; Partition Coefficient; Liposome; Lipid bilayer; Lipid Membrane; ORAC; Comet assay; Flow Cytometry.
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Emulsions containing three different types of milk fat fractions (MF13, MF27 and MF42) and anhydrous milk fat (AMF) were prepared at oil to water (O/W) ratios of 1:9, 3:7, 5:5 and 7:3 using rhamnolipids as emulsifiers. The prepared emulsions were analyzed for their storage stability and properties (colour, particle size, zeta potential and rheology). The effects of various factors (freezing/thawing, heating, pH, salts and ionic strength) on the stability of emulsions were also investigated. All emulsions prepared with an O/W ratio of 7:3, regardless of the type of milk fat, rendered a highly condensed, semi solid and cream-like substance whereas other emulsions containing less oil were in a liquid form. Among the four different O/W ratios tested, the highest emulsion stability during the storage of 12 weeks was observed from the emulsions containing 1:9 O/W ratios, due to a combine effect of smaller emulsion particle size and lower collision frequency between droplets. Interestingly, the emulsions with 7:3 O/W ratios were found to be more stable than the ones with 5:5 O/W ratios. This might be due to the limited movements of closely-packed emulsion droplets induced by the high oil concentration of 7:3 O/W ratios. The emulsion stability was significantly affected by low pH, especially at lower than pH 4, due to the loss of electrostatic repulsions between droplets leading to droplet coalescence and also possibly due to hydrolysis of rhamnolipid molecules. The presence of salts (NaCl, KCl and CaCl2) also rendered the emulsion unstable. The degree of instability was gradually increased with increasing salt concentrations. CaCl2 had the most significant effect even at a very low concentration. The viscosity of emulsions increased with increasing oil concentration but was not affected by the types of milk fats. Emulsions with 3:7, 5:5 and 7:3 O/W ratios exhibited non-Newtonian and shear thinning flow behaviour. At 7:3 O/W ratios, MF13 exhibited gel-like properties whereas both MF42 and AMF emulsions became more solid-like at higher frequency.

A series of experiments were devised in order to establish the relationship between fibre addition to an extruded breakfast cereal base recipe and the physical, chemical and nutritional qualities of the breakfast cereals. A twin screw extruder was used for all experiments. Preliminary investigations using, guar gum and inulin additions, illustrated that screw configuration was important in determining the physical properties (degree of expansion, firmness and crunchiness) of the extruded products. Thus a screw configuration featuring a reverse screw and mixing zone within the barrel was selected for the larger research study. In the extended experimental design guar gum, inulin, wheat bran, swede fibre, and hi-maize were added to a base recipe at; 5, 10 and 15 % of total dry ingredient content. A further experiment was completed to investigate the synergistic effects of adding differing fibres in combination. Results illustrated that soluble dietary fibres (for instance guar and inulin) created a porous, less firm, but crispier breakfast cereals than the insoluble fibres, which generally produced denser, harder products. The inclusion of fibre into the extruded breakfast cereals did not affect the chemical composition of the breakfast cereal significantly (P=0.05) when taking into account the diluting factor of adding the fibre into the base recipe. However moisture loss / retention on extrusion varied significantly (P=0.05) between fibre combinations. Thus the moisture loss of samples containing guar or inulin were greater than those samples containing wheat bran and swede fibre. The process of extrusion did not significantly effect the amount of protein, starch or fibre in the samples when the extruded samples were compared to the control samples. Pasting properties of samples were evaluated using the Rapid Visco Analyser. This was conducted to try to determine associations between starch pasting properties (gelatinisation events) of the raw and extruded samples and the physical or nutritional quality of the products. However, the results did not show clear associations. An in vitro analysis was conducted to determine the effect of fibre addition on starch breakdown and subsequent release of reducing sugars. Breakfast cereals which included wheat bran, guar and swede fibre all showed a reduced rate of starch degradation compared to the control (P=0.05). These fibres appeared to inhibit the rate of enzyme degradation of starch, in effect increasing the amount of slowly digestible starch in the breakfast cereals. Cereal samples containing inulin did not show this pattern. Generally the rate of inhibition was related to the amount of fibre added to the base recipe. When used in combinations, samples containing inulin and hi-maize were not significantly different to the control in terms of reducing sugar release, whereas inclusion of guar gum significantly reduced this release. In conclusion, the addition of selected fibres can be used effectively as a method of manipulating the starch degradation rates of extruded breakfast cereals. This has nutritional implications in terms of glycaemic index and loading of breakfast cereals. Further work is required to develop clearer associations between the events of starch gelatinisation during extrusion and the potential glycaemic response.

Sweet-potato contains a limited amount of protein, although rich in dietary fibre content and carbohydrate, so a successful combination with wheat flour for bread and biscuit production would be nutritionally advantageous. In particular, the role of these ingredients in relating to acceptability of breads and biscuit with higher percentage of sweet potato starch, flour in wheat flour. In this study, starch, flour and residue fibre of three sweet-potato varieties (red, orange and white -types) were studied. The 5 -10% combination levels for biscuit-making were found to be acceptable, without affecting the quality of the biscuit (combination of texture and biscuit size). In bread, bread containing 15% red and white replacement starches and orange replacement flour was found to be acceptable level, without affecting the quality of the bread, in an attempt to replace wheat at higher per cent level. The physicochemical study was complemented with a nutritional study to determine beneficial effects of food rich in dietary fibre and starches, in the context of improving diet related problems. RVA results showed sweet-potato ingredients affected differently the pasting temperature, peak viscosity and final viscosity of the normal wheat flour (p<0.05). Fibre inclusion showed large reduction in viscosity and swelling of sweet potato starch. Biscuits and breads containing sweet-potato starch and flour are low in amylose, and digest slowly because of lowly oriented and ‘crystalline’ areas within the granules enable to swell or to ungelatinised starch granules, whereas wheat control biscuit was able to gelatinised starch and exerted a greater effect upon digestibility. There are many other factors that need to be considered when analysing the in vitro starch digestibility such including amylose content, amylopectin structure and presence of fibre and gelatinising. Sweet-potato starch, flour and fibre addition show least effect on bread texture and size and starch, flour and fibre replacement. However, in in vitro starch digestibility test higher values RSS was recorded for starch addition followed by flour addition.

Limes (Citrus latifolia Tanaka) are an attractive fruit crop but generally suffer a loss in value as their colour changes from green to yellow. Various approaches were taken to slow degreening including low temperature storage, use of controlled atmosphere (CA) environments, and treatment of fruit with physiologically active agents such as gibberellic acid (GA3). However, the cold storage life of lime fruit can also be restricted by a number of factors including chilling injury (CI) and rots. Various pretreatments such as the use of fungicide (thiabendazole, TBZ) and hot water dipping (HWD) and several postharvest regimes based on temperature conditioning (step down technique) and intermittent warming (IW) regimes were further investigated to protect the fruit against rots and CI during cold storage. The objective of this study was to determine what storage conditions and pretreatments would permit long term storage of NZ limes with minimal loss of quality. CA storage (10% O2 with 0 or 3% CO2) was compared to regular air storage (RA) and IW (varying durations) treatments across a range of temperatures. Although some CA storage regimes could assist in delaying degreening, none of the treatments provided protection against CI. CA storage at 3% CO2 delayed yellowing and gave better fruit quality than the low CO2 treatment. High CO2 CA treatments at 5 or 7°C decreased the rate of colour change compared to other constant temperature treatments but did not protect against CI. CI limited storage of fruit under all conditions at constant low temperatures. Including fungicide (TBZ) in the dip water reduced the incidence of rots and had a secondary effect on protection against CI of lime fruit. However, fungicide use may sometimes exacerbate stresses such as heat injury on lime peel. Hot water dipping has been shown previously to hold potential as a storage pretreatment, but this technique may give risk of damage on produce if it is dipped at too high a temperature. Some HWD treatments did delay degreening, but there was no major effect on CI. HWD at > 47°C for = 4 min caused heat injury to NZ limes. All HWD treatments showed severe CI (>15%) after 10 weeks of cold storage; and HWD fruit stored under RA at 13°C did not show any CI but showed some pitting (= 10%) and degreened rapidly. Overall no suitable HWD treatment for limes was identified in this trial. This project identified the critical periods and temperature conditions for successful IW of limes. The IW conditions successfully delayed losses in quality of lime fruit provided the first warming period was applied within the first 20 days of storage. At least 2-cycle IW was required to maintain lime quality during long term storage. Some benefits were found after just one cycle of IW treatment but there were not enough to extend storage life. IW storage benefited fruit quality and provided the highest overall fruit quality of all postharvest treatments tested. The degreening of lime during cold storage at 5°C could be delayed by IW treatments in which the fruit were stored at 5°C for 12, 16 or 20 days then moved to 15°C for 2 days. Both 2- and 6-cycle IW treatments proved satisfactory for maintaining colour on the green and yellow side of lime for 12 weeks of storage. IW treatments in which fruit were warmed within 20 day of cold storage did not show significant CI symptoms after 12 weeks of storage, and the 2-cycle IW treatment showed only a low percentage of CI fruit at this time. A 2-cycle IW treatment was almost as effective as 6 cycles, and a step down treatment also showed some promising results, indicating that it may be possible to further optimize the time and duration of variable temperature storage regimes to meet both quality requirements and the constraints of temperature management in commercial coolstores. The application of these regimes to other citrus species may also be beneficial. There are a number of physiological explanations that may account for the effectiveness of IW including positive effects on heat shock protein (HSP) and cell membranes. Nutritional factors such as vitamin C and flavonoid compositions were also investigated and fruit that did not show visible CI were found to retain at-harvest levels of these factors. Practical ways of implementing IW are discussed. In order to understand the effectiveness of IW on degreening, I used a logistic model to describe degreening of lime peel. This modelling approach demonstrated that IW did not change the mechanism of lime degreening based on the similarity between the hue values predicted by the model and the actual hue values measured during lime storage. The activation energy (Ea) for degreening based on either hue angle (H°) or colour score (CS) during air storage was estimated to be ~53 and ~86 KJ.mol-1, respectively. Relationship between colour (H° and CS) and chlorophyll content, relationship between reflectance spectra (%), chlorophyll content and H° of lime fruit stored under different conditions are presented and discussed. This data allowed deduction to be made about the changes in individual pigments that are driving colour change during “good” and “bad” storage.

Colour is one of the main sensory characteristics of berry juice and fruit products and this parameter also powerfully impacts on consumer behaviour. However, the colour of berry juices is unstable and degradation occurs during storage. The main objectives of the project were: to determine the mechanism by which boysenberry juice enhances the colour of other berry juices and to determine if its addition to berry juices will also stabilise the anthocyanin pigments and enhance copigmentation. In this study, total anthocyanin, total phenolic acids, hyperchromic and bathochromic shift and the rate of colour degradation was measured by spectrophotometric techniques. Individual anthocyanin and phenolic acid content were measured in each juice by high performance liquid chromatography (HPLC) were evaluated during storage at 5, 20 and 35?C. Boysenberry juice improved the colour of blackcurrant, cranberry and pomegranate juices immediately after addition; however, only blackcurrant juice colour was stable during storage at 5?C. There was no influence on the stability of total anthocyanins in pomegranate or cranberry juices when boysenberry juice was added. Of the three juices, pomegranate had the highest rate of degradation. The total anthocyanin of blackcurrant enhanced with boysenberry juice was more stable than for cranberry and pomegranate juices. The impact of phenolic acids found in boysenberry juice (kaemferol, quercetin and ellagic acid) on blackcurrant juice colour stability was also investigated. The colour stability of blackcurrant juice was improved by the addition of ellagic acid at 5?C; however, the colour intensity of blackcurrant enhanced with kaemferol and quercetin decreased with storage. The copigmentations between anthocyanins themselves were not found to be a significant effect on colour stability of blackcurrant juice. Ellagic acid had the strongest colour improvement in blackcurrant juice compared to boysenberry juice. In conclusion, ellagic acid as found in boysenberry juice formed intermolecular copigmentation with blackcurrant juice anthocyanins, so this resulted in stabilised juice colour during storage; however, the effect was found when the juice was stored at 5?C only.

Cheese is one of the most well known food products in the world dating back to the 8th century B.C. There are more than 2000 varieties of cheese that are manufactured all over the world. Feta cheese is a soft white cheese with a salty and slightly acidic taste, which has originated from Greece. Most of the feta cheese manufactured in Greece is consumed locally, the migration of greeks to other parts of the world led to a demand for feta cheese outside of Greece. The spreading of the popularity of feta cheese to other ethnic groups in different parts of the world resulted in the high demand for feta cheese worldwide. The modern and most efficient method of feta cheese production involves a membrane filtration method, known as ultrafiltration. The ultrafiltration process utilises pressure as a driving force to concentrate milk by removal of water and small dissolved molecules. Hollow fibre and spiral wound ultrafiltration membranes are the two types of membranes that are commonly used for cheese production. An extensive amount of research exists on the implementation of ultrafiltration to improve the efficiency of the cheese making process and the performance of the membranes. However, limited research has been conducted on the comparison of the hollow fibre and spiral wound membrane performance in the cheese making process. The objective of the research was to determine if the hollow fibre membranes used at Puhoi Valley Cheese can be replaced with spiral wound membranes without compromising the quality of cheese produced. In order to achieve the objective, feta cheese was produced using hollow fibre and spiral wound ultrafiltration pilot plants. The operating performances of the hollow fibre and spiral wound membrane units were compared. To ensure that the quality of cheese is maintained, the cheese manufactured on the pilot plant units was analysed in terms of composition, microbiology, texture and sensory properties. The cheese made using the hollow fibre membrane pilot plant was compared with the reference sample from Puhoi Valley Cheese as they use hollow fibre membranes to produce feta cheese. The cheese made from the spiral wound membrane unit was also compared to that made by the hollow fibre membrane pilot plant unit. The operating parameters such as the inlet and outlet pressure, pressure difference along the membrane, transmembrane pressure, flow rate, recycle rate (bleed off rate), temperature and the run time were recorded. The operating parameters of the hollow fibre and spiral wound runs were compared with the data from Puhoi Valley Cheese. The quality of cheese made on the hollow fibre and spiral wound pilot plant units were evaluated in terms of composition, texture, microbiology and sensory properties. The composition was defined by the fat, protein, total solids and salt contents. The fat content was determined by utilising the modified Schmid-Bondzynski-Ratzlaff method, protein by the Kjeldahl method, total solids by using the air drying oven and salt percentage by the volhard method. The texture of the cheese was determined by the fracturability and hardness from the compression curve generated using the single bite compression test. The microbiological testing was performed according to New Zealand testing methods for E.Coli, Staphylococcus aureus, coliforms and yeast and mould. The difference from the control method was utilised for sensory evaluation. The acid degree value method was used to determine the lipase activity in feta cheese. It was found from the composition, texture and sensory analysis that the cheese from the hollow fibre pilot plant was different from the cheese manufactured at Puhoi Valley Cheeses (PVC). The spiral wound cheeses were also found to be different to PVC cheese, however the spiral wound cheeses and the pilot plant hollow fibre cheese were the same. The differences between both the pilot plant cheeses and PVC cheese were in terms of the fat, salt, moisture contents and the lipase activity in the cheeses. The fat content in the hollow fibre and spiral wound pilot plant cheeses are lower in comparison to the PVC cheese. This difference in fat content is considered to be due to the difference in the fat to protein ratio of the milk concentrated on the pilot plant and the PVC ultrafiltration system. The lower fat content resulted in firmer cheese than PVC due to more cross linking between the protein strands in cheese. The salt content in the cheeses made using the hollow fibre and spiral wound pilot plants was lower than Puhoi Valley Cheese. This is considered to be due to the low ratio of brine volume to cheese volume used for salting the cheese. The salt content of brine decreases during brining; hence a low ratio of brine volume to cheese volume causes a significant decrease in brine concentration. The decrease in brine concentration decreases the salt intake of the cheese. As salt diffuses in the moisture diffuses out, lower salt content results in higher moisture content in the cheese. As mentioned, the moisture content of the hollow fibre pilot plant cheese was higher than the PVC cheese. The moisture content is inversely proportional to the total solids, hence higher moisture in pilot plant cheeses implies lower total solids than the PVC cheese. The lipase activity results showed that the hollow fibre and spiral wound pilot plant cheeses had higher lipase activity than the Puhoi valley cheese. The differences in lipase activity of the pilot plant cheeses and Puhoi Valley cheese were considered to be due to the incomplete inactivation of lipase present in milk during pasteurisation. The results from texture and sensory evaluation support the above mentioned differences. The microbiology results for all pilot plant cheeses were within the trigger limits set by Puhoi valley cheeses. The results from monitoring the operating parameters of both the pilot plant data show that the permeate flux decreases while the total solids in milk increase with time, which was also observed from the Puhoi Valley Cheese data. However, the rate of decrease of the permeate flux and the increase of the total solids in milk are dependent on the membrane area, feed volume, transmembrane pressure, pressure drop across the membrane and the flow characteristics. The rate of decrease in permeate flux and the rate of increase in the total solids of the hollow fibre runs and spiral wound runs are slightly different. The difference is due to the availability of larger membrane surface area and processing of larger feed volume of milk in the spiral wound runs. The transmembrane pressure and the pressure drop across the membrane were maintained as close as possible to Puhoi Valley Cheese. In conclusion, spiral wound membranes can be used to achieve the desired total solids concentration and successfully make the same feta cheese as the hollow fibre pilot plant. In order to make the same quality of feta cheese as Puhoi Valley Cheese using the spiral wound membrane pilot plant, the same composition of milk used for concentration at Puhoi Valley Cheese needs to be used on the spiral wound pilot plant unit. It is recommended that Puhoi Valley Cheeses should be replaced with spiral wound membranes if they are more economical in terms of cost than the hollow fibre membranes.

The overall aim of this thesis is to determine if the interactions between normal and waxy rice starch and milk proteins from four milk protein ingredients, namely skim milk powder (SMP), milk protein concentrate (MPC), sodium caseinate (NaCAS) and whey protein isolate (WPI) do occur, and to identify the mechanisms underlying these interactions. Different milk protein ingredients at various concentrations (0 to 10%, w/w) affected markedly and differently the pasting behaviour of 10% (w/w) rice starches. SMP delayed the pasting of both rice starches by increasing the onset temperature (Tonset) and the peak viscosity temperature (Tpeak) of pasting. This was mainly due to the presence of lactose and ions, which was further supported by the investigation of the effects of UFSMP (a solution of salts and lactose present in SMP at their proper concentration) and lactose. The addition of NaCAS also delayed the pasting of rice starch; Tpeak in the case of both starches was increased. For normal rice starch paste, MPC and WPI decreased the Tpeak. MPC had no affect on Tpeak of waxy rice starch paste. The qualitative viscoelastic behaviour of rice starch/milk protein ingredient gels obtained from the above pastes was dominated by the continuous phase made of the starch molecules. There was evidence, as indicated by confocal microscopy, of phase separation between the milk proteins of SMP and MPC and the two starches. The phase separation was not observed in the addition of either NaCAS or WPI. Studies on the thermal behaviour of rice starch/milk protein ingredient mixtures by differential scanning calorimetry (DSC) showed that SMP, similarly to UFSMP, delayed the gelatinization of both starches. NaCAS also delayed the gelatinisation of both starches but had a greater effect on waxy than normal rice starch. The addition of NaCAS did not affect Tonset but increased Tpeak for normal rice starch, whereas the gelatinisation temperature of waxy rice starch was highly affected by the addition of NaCAS with both Tonset and Tpeak shifted to higher temperatures. MPC had no affect on the gelatinization temperature of normal rice starch, whereas the gelatinization temperature of waxy rice starch was increased by the addition of MPC. The addition of WPI to both rice starches showed two thermal transitions. The first of these was due to the gelatinisation of the starches and the second to the denaturation of ß-lactoglobulin (ß-lg). The addition of WPI to normal rice starch showed that the thermal behaviour of normal starch and protein were independent from each other. In contrast, the thermal behaviour of waxy rice starch was modified by the addition of WPI; both Tonset and Tpeak were increased. SMP decreased the Tonset of swelling, swelling ratio and the amount of starch leaching from both starches. These observed changes were due to the presence of lactose and ions in SMP. NaCAS slightly increased Tonset of swelling but the amount of starch leaching was reduced for both rice starches. The rigidity of both starches tended to increase in the presence of NaCAS. MPC and WPI affected the swelling behaviour of normal and waxy rice starch differently. A dramatic increase in the swelling of normal rice starch/MPC or WPI mixtures was observed, whereas this trend was not evident for waxy rice starch/ MPC or WPI mixtures. The difference in the water holding ability and gelatinization peak temperatures of the two starches over the temperature range at which whey proteins denature and form gels are believed to be responsible for the observed differences. The results from confocal microscopy showed that milk proteins, such as a-casein, ß- casein, ß-lg and a-lactalbumin (a-la), were adsorbed onto the granule surface of both normal and waxy rice starch. The mechanism for this adsorption is the hydrophilic interactions; hydrogen bonds between hydroxyl group from terminated glucan molecule that protrude around starch granule surface-hydroxyl; amino, or other electron-donation or electron-accepting groups of the added proteins. Using sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE) it was found that for SMP and MPC the adsorbed as- to ß-casein ratio on both starches was similar to the as-casein to ß- casein ratio in the casein micelle at low SMP and MPC concentrations. But at high concentrations of SMP or MPC, this ratio decreased indicating that more ß-casein was adsorbed preferentially to as-casein. In the case of NaCAS, as-casein was adsorbed preferentially to ß-casein. Moreover, there was evidence of multilayer adsorption of ascasein into the surface of rice starch granules. Compared to the other milk protein ingredients, very small amounts of the ß-lg and a-la from WPI were adsorbed onto starch granules. However, the adsorbed amounts of ß-lg and a-la from WPI continuously increased with increasing WPI concentration, suggesting that these two proteins, particularly ß-lg, adsorbed in multilayers too.

Fouling of heat treatment equipment in the dairy processing industry is an expensive and persistent problem. The objective of this work was to develop a better understanding of the mechanisms of dairy fouling in heat exchangers and identify methods to control this build-up. This was part of a larger project investigating the interaction between spore-forming thermophilic bacilli (thermophiles) contamination and fouling deposits on internal surfaces of equipment. Two systems were developed to monitor the onset and build-up of fouling on the internal surfaces of two research heat exchangers. The first used a commercial sensor to measure the local heat flux and the temperature on the hot side of a plate type heat exchanger. The heat transfer coefficient was calculated and normalised with its value at the start of the run to reflect the contribution of fouling deposits to the thermal resistance, thus giving a real-time estimate of the rate of fouling. The second system used an energy balance over a tubular type heat exchanger and measured inlet and outlet temperatures to estimate the overall heat transfer coefficient thus giving a global measurement of fouling over the tubular heat exchanger. In both systems the plot of normalised heat transfer coefficient over time often stayed constant over an induction period, which was followed by a falling period indicative of growth in the fouling layer thickness and/or mass. Each system was validated by comparing the final value of the normalised heat transfer coefficient with direct measurements of fouling made at the end of a run namely: fouling deposit height for the local measurement and fouling deposit mass for the global measurement. The normalised heat transfer coefficient reported by each system correlated well with the corresponding direct measurement of the fouling layer. An important factor identified in this study was the effect of air bubble nucleation on fouling deposits. It was shown that bubbles that formed on the heated surface greatly reduced the length of the induction period to a matter of seconds rather than hours, as found in previous studies of fouling in the absence of surface bubbles. The rate of fouling was also enhanced while the bubbles remained at the surface. The structure of bubble type fouling layers was linked to the behaviour of the bubbles at the heated surface. Visual observations of these bubbles showed evidence of growth, vibration and coalescence during their period of attachment to the heated surface. Deposits from bubble type fouling consisted of all solid components found in the original milk solution, except lactose, in approximately the same ratio. By contrast fouling deposits reported in the literature with systems operating under the traditional protein denaturation mechanism were reported to consist mainly of whey proteins. Bubble induced fouling can be limited in a number of ways, the most effective being to maintain a high operating pressure in the equipment to ensure nucleation does not occur. Experiments conducted in this study showed that a pressure of 130 kPa.g was sufficient to suppress all bubble nucleation at the heated surface at a temperature of 90°C. Another method identified was the use of high linear fluid velocities to entrain any surface bubbles into the processing stream immediately upon nucleation. Linear velocities above 1.0 m/s were shown to achieve this goal in the miniature plate heat exchanger tested. However, this method is only partially successful because the local linear velocity varies with position in heat exchange equipment of complex geometries and can drop below the mainstream average velocity causing surface bubbles to form, especially in recirculation regions behind flow obstacles. A more reliable method, in situations where high operating pressures could not be used, involved conditioning the heated surface with a thin protein layer during the first few minutes of a run. Conditioning the surface resulted in bubble suppression even at high temperatures and low pressures, thus greatly extending the length of the induction period. Trials performed in this study showed that the addition of a proteolytic enzyme produced by psychrotrophic microbes greatly increased fouling. The enzyme destabilised the caseins which could attach directly to the heat exchange surface independently from the bubble fouling mechanism. Thus the quality of the milk is another important factor to consider. However, the addition of enzymes produced by thermophilic bacilli isolated from milk powder plants did not increase fouling. A theory describing the air bubble induced fouling mechanism is presented along with recommendations on how to reduce this fouling contamination in processing equipment.

Plants are used to produce many secondary metabolites that are too difficult, expensive or impossible to make by chemical synthesis. Conventional cultivation of plants is of course subject to vagaries of weather, pests and availability of land; hence, the interest in highly controlled culture of plant cells and hairy roots in bioreactors as methods of producing various products. This project focussed on production of blue and red colors of Lavandula augustifolia and Beta vulgaris, respectively. Callus and suspension cell culture were successfully produced from L. augustifolia after extensive trials, but hairy roots could not be generated from this species. In contrast, a successful protocol was developed for consistently producing hairy roots from B. vulgaris, but calli could not be generated from this species. Effects of medium composition on growth of L. augustifolia calli and freely suspended cells and production of the blue pigment by the latter, were investigated. Optimal production of callus occurred in full-strength Murashige and Skoog (MS) medium supplemented with 2 mg/l of indole-3-acetic acid (IAA) and 1 mg/l of kinetin. Stable suspension cultures could be produced and maintained in full-strength MS medium supplemented with 1 mg/l each of IAA and kinetin. In suspension culture in full-strength MS medium, the following hormone combinations were tested: (1) 1 mg/l each of indole-3-acetic acid (IAA) and kinetin; (2) 2 mg/l of IAA and 1 mg/l of kinetin; (3) 2 mg/l of IAA and 1 mg/l of benzyl amino purine (BAP); and (4) 2 mg/l each of IAA and BAP. Combination (3) maximized cell growth, but the highest cell-specific production of the blue pigment was seen in combination (2), although pigment production occurred at all hormone combinations. The medium formulation that gave the best production of the pigment in shake flasks was scaled up to a 2 L aerated stirred tank bioreactor, but both the biomass and pigment productivities were reduced in the bioreactor apparently due to the high shear stress generated by the Rushton turbine impeller. Compared to suspension cultures of L. augustifolia, the hairy root cultures of B. vulgaris grew extremely rapidly. Hairy roots also produced large amounts of the red pigments. Growth of hairy roots was influenced by the composition of the medium. Although the full strength MS medium better promoted biomass growth compared to the half-strength MS medium, the final concentration of the biomass and the pigment were nearly the same in both media. Attempts were made to enhance production by using various hormones (i.e. naphthalene acetic acid, BAP, IAA added individually at a concentration of 0.5 mg/l), but none of the hormones proved useful. BAP adversely affected the growth of hairy roots. In summary, production of pigments by suspension culture of L. augustifolia and hairy root culture of B. vulgaris, is technically possible, but requires substantial further optimization for enhancing productivity than has been possible in this project. iii