Masters Theses

Date of Award

12-1961

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Husbandry

Major Professor

W.W. Overcast

Committee Members

B.J. Demott, T.B. Harrison, H.N. Carringer

Abstract

The dairy industry strives to provide the public with safe and wholesome milk and milk products having good keeping quality. This goal can be accomplished through quality control programs and accepted methods and practices in the production and handling of the milk and its products. Today’s longer shelf life requirement, however, makes it necessary for maximum attainment of sanitation through proper processing and handling practices in order to maintain good keeping quality.

The destruction of pathogenic or disease producing microorganisms which may be present in milk and cream is carried out most readily by proper pasteurization. This practice renders milk safe for human consumption unless otherwise recontaminated through careless handling practices. Likewise pasteurization destroys other microorganisms including the psychrophiles. The fact that psychrophiles are commonly found in pasteurized milk of today is an indication that they have been introduced at one or more points during post-pasteurization handling on the product. This suggests an inadequate sanitizing operation.

Rapid cooling of processed milk can temporarily slow the growth rate of bacteria present as a result of post-pasteurization contamination or faulty pasteurization. This would appear to make possible an effective masking of unsanitary processing practices if standard plate counts prepared from these milk samples taken immediately after processing are relied upon wholly as the quality control check.

Johns (16) has shown that shortcuts in dairy farm sanitation programs can be effectively masked if efficient cooling equipment is employed to the extent that bacterial growth rates are temporarily retarded. Bacteria counts made soon after production on rapidly cooled milk from such a farm are inadequate since they may indicate better than actual quality. Preliminary incubation of milk samples from these farms before plating, however, causes growth of these “hidden” bacteria; the extent of which is an indication of these level of sanitation achieved during production.

It would appear that such a treatment would be applicable to pasteurized milk in determining the degree of post-pasteurization contamination or the initial pasteurization efficiency, and to some extent, provide a basis for predicting the keeping quality of the milk.

The purpose of this investigation was to determine and observe the coliform, psychrophilic, and total bacterial counts of freshly pasteurized milk from the Knoxville, Tennessee market area and to compare increases in coliform or total counts brought about by a twenty-four hour preliminary incubation at 15.5° and 18.0° C. with the keeping quality and milk plant inspection records.

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