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A. A. GLUECK and C. H. White. Food Science and Technology, Mississippi State University, Box 9805, Mississippi State, MS 39762

The ability to rapidly predict "potential" shelf life of finished milk products is extremely important to dairy processors. Identifying accurate, rapid and economical tests to detect the presence of contaminants such as psychrotrophs is essential in increasing the keeping quality of fluid milk products.

Our objective was to evaluate results of five microbiological tests and their correlation with the shelf life of milk.

We determined the shelf life of whole chocolate and reduced fat milk samples from four different dairy plants. Ten samples of whole chocolate milk in half-gallon jugs, ten samples of whole chocolate milk in pints, ten samples of reduced fat milk in half-gallon jugs and ten samples of reduced fat milk in pints were collected from each of four plants. The experiment was thrice replicated. Samples were evaluated through preliminary incubation (PI) of product at 21 C for 18 hours followed by standard plate count (PI + SPC), crystal violet tetrazolium (PI + CVT), violet red bile (PI + VRB), penicillin (PI+PEN), and bioluminescence (PI + ATP). Samples were stored at 7 C for seven days. Sensory evaluation was conducted at day 7, day 10, and every other day thereafter until off-flavors resulted.

Shelf life for half-gallon reduced fat milk ranged from 9.93 to 13.66 days and 7.16 to 12.46 days for reduced fat pint milk samples. Whole chocolate half-gallon shelf life ranged from 8.60 to 10.63 days and 9.16 to 11.36 days for whole chocolate pints. Out of sixteen product/plant/size combinations PI + CVT had the highest correlation with product shelf life 10 times, PI + bioluminescence had the highest correlation three times, while PI + VRB had the highest correlation with shelf life twice and once for PI + PEN.