17B-6 |
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W. BANG, D. A. Clare, M. A. Drake, and J. Simunovic. Dept. of Food Science, North Carolina State Univ., Schaub Hall, Box 7624, Raleigh, NC 27695-7624 Consumer acceptance and market penetration of shelf stable milk could benefit from sensory quality improvement. Current methods of heating cause flavor and nutrient degradation through exposure to overheated heat exchange surfaces. Rapid heating with microwaves followed by rapid cooling could reduce or eliminate this problem. The objectives of this study were to design and implement continuous thermal processing for shelf stable milk using continuous microwave and aseptic packaging and to compare sensory, microbiological, and chemical effects of conventionally processed UHT and microwave processed milk. Skim and whole fluid milk (white and chocolate) were processed by conventional UHT and microwave heating with aseptic packaging. Samples were stored at ambient temperature for 12 months. Every three months, samples were taken for microbiological analysis, descriptive sensory evaluation, active enzyme analysis, and instrumental viscosity and color. Microbiological tests were negative on all milks at each timepoint. Alkaline phosphatase and plasmin assays were negative. DTNB (dithionitrobis-2-benzoic acid) measurements, a measure of free sulfhydryl (-SH-) groups, were higher in conventional processed milks in contrast to the microwave-exposed samples. Sulfhydryl oxidase, a milk enzyme that catalyzes disulfide bond formation using various protein substrates, was most active in the microwave processed samples and in all cases, enzymatic activity decreased during storage. Conventionally heat processed milks displayed darker color and higher caramelized flavors than microwave processed milk. Stale/fatty flavors increased in milks with storage time. Sensory effects were larger in white milks than in chocolate milks. Microwave processed milks may provide an alternative to conventional UHT processing.
Session 17B, Dairy Foods: General
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