Masters Theses

Date of Award

3-1963

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Husbandry

Major Professor

B.J. Demott

Abstract

The development of off-flavors in dairy products is sometimes intricate. It is very important to the dairy industry that a knowledge of the causes and prevention of these off-flavors be gained since flavor is perhaps the most important single factor in determining the consumer acceptance and saleability of dairy products. There are some flavors, disagreeable in themselves, which directly affect the saleability of the product, since they are quite evident to the consumer. There are other flavors not particularly disagreeable nor even noticeable to the average consumer which are believed by the buyer to indicate poor keeping quality. The cooked flavor belongs in the former category. Relatively recent reviews of off-flavors in milk have been made by Strobel, Bryan and Babcock (48). The heat treatment of milk produces chemical changes in milk resulting in flavors not pleasing to the taste and smell, for example, cooked flavor. The lack of complete knowledge about the chemical nature of these flavor producing substances complicates the problem of evaluating the means of removing them from milk and dairy products. Taints in milk and dairy products have been removed partially or wholly by: (a) Dilution or washing with water or a light weight mineral oil. (b) Aeration with and without reduced pressure. (c) Application of vacuum. (d) Distillation with steam, usually under controlled pressure. The primary function of vacuum is to accelerate the removal of flavor laden vapors and to assist in temperature control. Lowering the temperature and pressure, i.e., increasing the vacuum applied; (a) would facilitate the removal of low boiling substances (b) may facilitate or may retard the removal of substances with boiling points close to that of water; and (c) would definitely retard the removal of high boiling substances (43). Questions which remain yet to be answered include: (a) what is the chemical nature of tainting substances? (b) what is the particular combination of time, temperature, vacuum treatment that is most effective and efficient for removal of off-flavors? (c) can chemical tests be developed for the tainting substances, so that more objective means will be available for evaluating the treatment combinations? (d) can the treatments be adapted to enough of the dairy products to insure greater economy in the use of the equipment? (e) can the equipment be adapted to remove chemical substances that are not affected by present treatments? Studies on the heat volatile sulfides of milk have assumed special importance since work has been reported indicating that the liberation of these sulfides and the formation of sulfhydryl groups may be closely allied with the production of the cooked flavor and with the prevention of the oxidized flavor in milk (19,30). The results secured in these various sulfides studies have been based largely on qualitative determination. Quantitative determination and the influence of time and temperature have been reported (52). Influence of time,temperature and vacuum on the sulfhydryl production and subsequent development of cooked flavor has not been studied so far, therefore, the present work was undertaken to study the influence of various combinations of time, temperature and vacuum levels on the production of sulfhydryls in milk during heat treatment. The influence of various levels of vacuum treatment on the development of cooked flavor in milk is reported.

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