A Study of Some Physico-Chemical Changes in a Spread-Type Dairy Product During Storage

In the Dairy Science Department at South Dakota State University a new dairy spread product has been developed which has only 50% of the fat content of butter or margarine and 60% of the calorie value of the higher fat products. It is increased in solids content with nonfat milk solids. The purpose· of developing this product was to obtain a new outlet for milk constituents; desirably it was to be one that could regain the market sales which were lost by butter and are now enjoyed by the margarines. The high price of butter compared with the substitute product has been an important factor in the displacement of the consumer\u27s acceptance. The reduction in fat percentage to half the content of butter made it possible to cut down the ingredient costs, for fat is the most expensive constituent. At the same time spreadability over a wide temperature range which even allows one to spread the product immediately after removal from storage in a home refrigerator, an improved flavor, and an increased proteinic value are additional desirable characteristics of this new product. Recently the people who worked on its development hopefully presented the formula, processing data, and offer of technical aid to the dairy processors of South Dakota. The presentation was accompanied by comments on the qualities and possibilities of the product. Since developmental work on the product was started, keeping quality had been closely observed and judged continuously. Tests and observations indicated the need of some changes in the composition and/or procedures to improve and extend the period that the product could be stored and remain an acceptable food product. It had been observed that the dairy spread did tend to soften during storage. It was thought that this change in the body and texture involved some protein transformation and/or changes in their water holding capacity. It was thought, therefore, that an electrophoretic migration study of milk proteins in the dairy spread during a storage period of at least 3 months would be useful to indicate whether the presumed changes actually occurred. Variations in the redox potential have been reported to be connected with changes on the diacetyl level content since acetoin can be oxidized to diacetyl and diacetyl in turn readily oxidizes to 2, 3 butylene glycol. Of these three, only diacetyl contributes flavor to foodstuffs. Since ascorbic acid was known to play an important role in the Oxide-reduction equilibria of milk and milk derivatives, it was apparent that any study of the oxidation-reduction system in the dairy spread would of necessity involve quantitative determination of ascorbic acid. Protein sulfhydryl (-SH) groups are quite reactive, and contribute antioxygenic properties to milk proteins which have been heated to denaturation temperatures, as has been demonstrated by many workers. Their presence was supposed to be connected with the physico-chemical changes and to be a major factor in the oxide-reduction equilibria. They were evaluated quantitatively with a modified amperometric titration. It was hoped that determinations of the actual redox potential and quantitative determinations of two major constituents affecting the redox equilibria would shed some light on the interrelationships between redox potential and the flavor of the dairy spread. Since it had been evident during developmental work on the dairy spread that both the total and relative quantities of protein, fat, total solids, and moisture affected body, texture, and flavor of the product; and since the viable bacteria content had an obvious influence on keeping quality and oxygen content of the dairy spread; it was elected to follow the contents of these factors during the storage trials