17D-12 |
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C. O. MADUKO, Dept. of Food Science & Technology, Univ. of Georgia, Food Science Bldg., Athens, GA 30602 and Y. W. Park, Agricultural Research Station, Fort Valley State Univ., 1005 State University Dr., Fort Valley, GA 31030-4313. Optimization of physico-chemical stability and microbial population are of great importance for development of formulated foods. Protein aggregation, gelation and sedimentation are crucially influenced by viscosity and pH of food ingredients. The aim of this study was to compare changes in viscosity, pH and microbial populations between different types of caprine milk stored under refrigeration. Three batches of 3 types of goat milk: raw milk (RM), sterilized milk (SM; 140oC for 3 second) and reconstituted milk (RCM; 12.5 g spray dried goat milk dissolved in 87.5 ml deionized water) were prepared and stored in a refrigerator at 4oC for 14 days. Viscosity was measured using a viscometer (Brookfield Engineering, Inc. LVDVII), pH was determined, and microbial populations were enumerated for total aerobic, E. coli, coliform, Staphylococcus aureus, yeast and mold counts using 3M Petrifilm techniques. Viscosity ranged 4.40 - 4.61 centipoises for all tested goat milk samples throughout the experiment, where no differences in viscosity were found among three types of the caprine milks. Respective ranges of pH for RM, SM and RCM were: 6.56-6.59; 6.34-6.66; 6.34-6.63, suggesting that pHs of the sterilized and reconstituted milks had slightly lower and wider ranges compared to those of RM. The pHs were significantly (P<0.05) increased from day 7 for both SM and RCM. Low pHs in SM and RCM up to day 5 might be attributable to the acid production from lactose degradation by drastic heating (sterilization, spray-drying). No particle sedimentation was observed, but surface gelation occurred at day 6 and 14 for SM and RCM, respectively. All bacterial counts of RM were TNTC, while those of SM and RCM were negligible at least up to 5 days storage. The surface gelation in SM and RCM appeared to be accountable for heat treatment and refrigerated storage rather than septic or enzymatic spoilage.
Session 17D, Food Chemistry: Chemical effects of food processing and preservation
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