Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Dairy Science


One of the most significant problems in the dairy industry today is the flavor defect known as rancidity. This defect has been recognized for some time, but recent trends in milk handling have increased the problem of rancidity. Recently the dairy industry on the farm has changed to the increased use of pipeline milkers and bulk handling of milk. Processing plants are becoming larger and more centralized, resulting in more movement over longer distances for the raw product. These changes result in increased foaming and agitation of the milk, contributing to the rancidity problem. The butter industry has changed. Butter processing plants are larger and fewer in number, and cream is often transported many miles. Butter is also kept in storage for longer lengths of time. United States Department of Agriculture (USDA) butter graders have detected increased incidences of rancidity in butter since 1971, and confirm that rancidity currently is one of the major problems in the butter industry. Butter production has always been a major sector of the dairy industry. During the last 25 years, the butter industry has utilized at least 16% of the annual milk production in the United States. This utilization had decreased from 23% in 1950 to the low of 16% in 1973, and then the trend reversed so that 17/4 of the U.S. milk production was used by the butter industry in 1975 (97). This recent increase in butter production emphasizes the importance of producing top quality butter. Butter makers cannot afford an increase in the incidence of rancidity, because this defect results in poor consumer acceptance and the down-grading of butter, which in turn results in lower sales prices. Both of these results lead to eventual economic losses to the butter industry and consequently to milk producers. The rancid flavor is characterized as unclean or bitter. It is primarily the result of action by the lipase enzyme system of milk, which causes the hydrolytic breakdown of milkfat. This hydrolytic breakdown results in the release of free fatty acids, and it has been demonstrated that the lower molecular weight fatty acids which are freed are the major contributors to the rancid flavor (12, 54, 115). This lipase enzyme complex, which is normally inactive in fresh milk, can be activated by agitation and temperature changes. It had previously been thought that pasteurization temperatures were adequate to totally inactivate the milk lipase system. Recent evidence, however, has indicated that the milk lipase system may be reactivated by certain temperature conditions, thereby enabling a milk product to undergo lipase deterioration during storage (23, 103). Organoleptic analysis has traditionally been used to determine rancidity. This method is subjective and identifies rancidity after it occurs so it gives no information on a product approaching rancidity. Titration and colorimetric methods have been used to measure total free fatty acids rather than only those of lower molecular weights, and appear to give unreliable results as far as measuring the deterioration by rancidity of butter during storage (9). A better test for rancidity would measure the quantity of the lower molecular weight acids only, but this type of analysis has not been reported. One objective of this study was to prepare butter samples of different qualities by subjecting cream to temperature fluctuations which resulted in, induced rancidity in the cream as well as the butter churned from it in order to simulate commercial conditions. Another objective was to study the effect of storage temperature and storage time on the free fatty acid levels of these butter· samples and to relate this information to the flavor degradation of the butter samples during storage.

Library of Congress Subject Headings

Fatty acids


Includes bibliographical references (pages 78-87)



Number of Pages



South Dakota State University


In Copyright - Non-Commercial Use Permitted

Included in

Dairy Science Commons