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    Effect of air temperature on the thermal degradation of heat liable products in spray drying and monodisperse drying : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Manawatū, New Zealand
    (Massey University, 2018) Sang, Xiaoqi
    Three heat liable protein-based materials β-galactosidase, whey protein isolate (WPI) and egg white (with 30-35% w/w total solids) were dried through conventional spray drying and monodisperse drying respectively with constant inlet air temperature 200 ℃ and different outlet air temperature. The purpose was to test the hypothesis that monodisperse droplet drying could produce more control over time-temperature experience during drying, resulting in reduced loss of structure or activity. The residual enzyme activity of the dried lactase product was determined by ONPG β-galactosidase assay, and the extent of denaturation of WPI and egg white was determined by differential scanning calorimetry (DSC). Particle size and morphology were also measured and observed. The results showed that for both spray drying and monodisperse drying, the extent of protein denaturation increased as outlet air temperature increased. In comparison with spray drying, monodisperse drying had a longer residence time using our particular apparatus and gave rise to higher extent of heat degradation for all three materials. The dried products from monodisperse drying showed a narrower particle size distribution but had larger particle size compared to the products from spray drying. The majority of monodisperse dried powders had a multivesicular hallow morphology due to high interior temperature and coalescence of neighbouring particle in flight. The feasibility of using monodisperse drying in real industry is still under investigation. Although the results obtained from this study denied the expectation that monodisperse drying can reduce the thermal degradation of product during drying process, they are still useful in developing the monodisperse drying system and optimizing the operating parameters.
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    The potential use of hen egg white lysozyme as an antimicrobial agent in foods : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University
    (Massey University, 1995) Rushizha, Edgar
    The potential use of lysozyme as an antimicrobial agent in foods was investigated in model food systems(brainheart infusion broth) using factorial designed experiments and in mussel and cottage cheese food systems. Optical density or absorbance was used as a tool to monitor the growth response of Listeria monocytogenes and C. tyrobutyricum in brain heart infusion broth under the combined influence of pH(5.5, 6.5), lysozyme (0.2mg/ml, 3mg/ml) and different chelating agents(ethylene diaminetetraacetic acid(EDTA), glycine, gluco delta lactone(GDL), citric acid, sodium phosphate dibasic(SPDB) and sodium hexametaphosphate(SHMP)(10mM, 25mM). Using 2 3 full factorial design experiments, the yield of the organisms (expressed as the area under the curve of a plot of change in optical density at 600nm vs time) was taken as the quantitative response variable for each treatment. These yield values were then used for (a) statistical analysis to determine which of the single or interactive factors tested significantly reduced the yield, (b) formulation of a mathematical regression equation which could be used to predict microbial growth within the limits of the factors studied. Diagnostic plots were constructed to evaluate further how well the statistical model fit the observed yield values. Plots of residuals versus predicted yield values appeared to suggest that a transformation of the response would improve the fit of the models. No other serious reservations were suggested by the diagnostic plots. Goodness of fit of the models was also evaluated by the R-squared values. Significant two-way and three-way interactions between lysozyme, pH and EDTA, GDL, citric acid and glycine were exhibited. Response surface methodology(RSM) was used to (a) characterize the response of L. monocytogenes to variation in treatment combinations and (b) show non-linearity of models(or interaction of factors). Generally yield was minimal in treatment where pH was low, with high lysozyme and chelator. Based on equal molar concentrations, the antimicrobial activity of the different chelating agents was in the order EDTA > GDL > citric acid > glycine > adipic acid > SHMP > SPDB. The same ranking was true for the degree to which each chelating agent enhanced lysozyme activity. Based on broth culture studies, the chelating agents EDTA, GDL, glycine, citric acid and adipic acid were demonstrated to have potential for use as antimicrobial agents in combination with lysozyme in food systems. Results of a 2 5 factorial design indicated that the 5 factors, lysozyme, GDL, pH, inoculum level and temperature were important in the inhibition of L. monocytogenes. Results of the broth culture studies gave a good reflection of the survival of L. monocytogenes in the food system. The variable combinations interacted to decrease the growth of L. monocytogenes and extended the lag phase duration. However C. tyrobutyricum was more tolerant to the different treatment combinations other than EDTA. A study of protein interference demonstrated that the antimicrobial activity of the lysozyme-GDL preservation system was not inhibited by the presence of proteins. The food system study demonstrated that the lysozyme-GDL treatment combination has potential for use as a preservative in refrigerated low pH ready-to-eat foods. The susceptibility of L. monocytogenes to lysozyme-GDL treatment in both broth culture and food systems increased as the temperature was reduced(25C-5C) and as the pH decreased(pH6.5-pH5.5). Food system studies demonstrated that modified atmosphere packaging(96.58%N2 , 2.09%O2 and 1.34% CO2) has no influence of the growth of L. monocytogenes. The susceptibility of L. monocytogenes to lysozyme-GDL was a stable characteristic, remaining unchanged during the entire study. Attempts to select for greater lysozyme-GDL resistance by testing populations grown from lysozyme-GDL survivors isolated at the end of the food system study was unsuccessful. There was no evidence that L. monocytogenes was resistant to the lysozyme-GDL treatment.
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    Iron binding properties of whey protein, casein, soya protein and egg albumen : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University
    (Massey University, 1993) Manvikar, Netra
    Iron binding properties of whey protein, casein, soya protein and egg albumen were investigated in aqueous dispersions using centrifugation and ultrafiltration techniques. Protein-iron mixtures were centrifuged at 10,800 g for 20 min and iron that co-sedimented with protein was considered to be bound to the insoluble protein fraction. The supernatants were ultrafiltered to obtain iron bound to the soluble protein fraction. Both the soluble and insoluble fractions of each protein were shown to bind substantial quantities of iron from ferrous sulphate. The amount of iron bound/g to the insoluble fraction of the protein was highest for casein (87 mg) followed by albumen (80 mg), soya protein (66 mg) and whey protein (63 mg). A similar trend was observed for the soluble fraction; casein bound 74 mg iron/g protein followed by albumen (68 mg), soya protein (54 mg) and whey protein (12 mg). This binding was markedly influenced by pH of the protein-iron mixtures in the range 2 – 7. The binding data was analyzed using the Scatchard equation to obtain binding constants (k) and the number of binding sites (n). The n values obtained were ~ 2 (whey protein), 13 (casein), 200 (soya protein) and 42 (albumen). The values obtained for the binding constants were ~ 11 (whey protein), 5 (casein), 3 (soya protein) and 1 (albumen). Thus soys protein had the highest number of binding sites and whey protein had the greatest affinity for iron. Solubility of each protein was dependent on pH and it generally decreased with increase in iron concentration. The effects of chelating agents (citric acid and ascorbic acid) on the iron binding properties of the four proteins were also examined. Addition of citric acid and ascorbic acid increased the solubilities of both protein and iron. The solubilizing effect of these two acids was dependent on the protein source, pH and acid concentration. Iron binding by both the insoluble and soluble fractions decreased in the presence of citric acid and ascorbic acid, with no significant differences between the effects of the two acids. The effects of proteins and protein digestion products on in vitro iron availability were studied. Ferrous iron complexes with protein were prepared and subjected to simulated gastrointestinal digestion followed by measurement of soluble iron. The in vitro availability of iron was in the order of 26% (soya protein), 16% (casein), 14% (albumen) and 10% (whey protein). When citric acid and ascorbic acid were added prior to enzymatic digestion the availability of iron increased to 63% (soya protein), 36% (albumen), 31% (casein) and 22% (whey protein).