A study was made of the keeping quality of market milk obtained from retail outlets and processing plants in Lexington, Ky., during 1963. Included were a total of 144 samples from retail outlets processed by 9 commercial plants and 92 samples obtained at 5 commercial processing plants.

Approximately 7, 16, 31, 58 and 74% of the retail outlet samples did not have a satisfactory flavor score after storage for 0 (date purchased), 4, 7, 10 and 14 days, respectively, at 40–42 F. The average keeping quality was 7.7 days from the date of purchase. The samples ranged from 0 to 14 days old when purchased, the average being 3.9 days. Approximately 2, 8, 52, and 83% of the samples obtained at the processing plants did not have a satisfactory flavor score after storage for 0 (date obtained), 3, 5, and 7 days, respectively, at 50 F. The majority of the samples possessed “psychrophilic” type defects at the time the flavor quality was judged unacceptable.

Initial standard plate, coliform, and psychrophilic counts were generally low. Standard plate counts (SPC) on the samples after storage were rather high.

Highly significant correlations were observed in samples obtained at retail outlets between the following individual factors: Initial SPC and age; initial SPC and SPC after storage; initial SPC and keeping quality; SPC after storage and age; SPC after storage and keeping quality; and age at purchase and keeping quality. The multiple correlation between keeping quality and age, initial SPC, and SPC after storage was 0.64. Highly significant differences were observed between plants with respect to age of samples when purchased, SPC after storage, and keeping quality.

There was a highly significant correlation between the keeping quality of the samples obtained from processing plants and the Moseley count. No significant correlations between keeping quality and SPC and psychrophilic counts were detectable. The multiple correlation between keeping quality and SPC, psychrophilic count, and Moseley count was 0.30. Highly significant differences were observed between plants with respect to keeping quality.

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Author notes

1The investigation reported in this paper (Journal article No. 64-6-56) was supported in part by Agricultural Marketing Act funds and is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director.

2Present address: U. S. Public Health Service, Washington, D. C.