Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Dairy Science

First Advisor

Thomas M. Gilmore


Yogurt is a highly nutritious cultured dairy product which has been consumed for centuries, particularly in Eastern Europe. Although per capita consumption in the United. States is still far below that of most European countries; yogurt sales in the U.S.A. have increased phenomenally during the past three decades. Yogurt sales in the U.S.A. totaled 7.7 million kg in 1955; 31.8 million kg in 1966; and approximately 227 million kg by 1976 (41). Per capita sales increased 211% from 1970 to 1980 (45). Yogurt is generally manufactured from milk or lowfat milk which has been fortified with extra milk solids. Nonfat dry milk (NDM) is the usual source of these milk solids, but NDM has been steadily increasing in price. The price of NDM has increased from $1.76/kg in 1979 (14) to $2.11/kg in 1982 (15), an increase of 20%. Less expensive but compositionally and nutritionally equivalent substitutes for NDM in the manufacture of yogurt, such as certain modified whey products, would seem to present an economically attractive alternative to the yogurt processor. The Whey Products Institute estimates approximately 18.2 million kg of whey were produced in the U.S.A. in 1980, of which less than half was processed and used in human foods (4). About 55% of the processed whey was concentrated and spray dried into a variety of products. Greater usage of these products in human foodstuffs has become possible because of greatly improved product quality attributed to better sanitation, handling, and processing methods. Many nutritious whey products, such as partially delactosed or demineralized whey powders and whey protein concentrates (WPC) with the proteins in an undenatured form, are available to the dairy processor. Depending upon the processing methods, the whey protein products possess a wide range of and nutritional properties which make possible variety of applications in food products (16). A major component of the milk solids in yogurt is the disaccharide, lactose. Lactase enzyme hydrolyzes lactose into glucose and galactose which individually and together are sweeter than lactose itself. The resulting sugar mixture is also more soluble (31), easily digestible by lactose intolerant individuals, and is more readily fermented by lactic acid organisms (52). In general, northern Europeans and their descendants and members of two African tribes are the only persons who retain their childhood ability to digest lactose as adults. An estimated 30 million Americans can not digest lactose properly and among certain ethnic groups (Blacks, Asians, Mediterraneans, Jews, Southern and Central Europeans, and American Indians), 70% have difficulty digesting lactose as adults (9). Hydrolysis of at least part of the lactose in milk prior ~o its manufacture into various products not only may be a potential partial solution to the lactose intolerance problem (31), but it may result in improved products with increased sweetness without increased calories (17, 31), increased carbohydrate solubility, and better mouth feel and body (3, 31). One objective of this research was to determine the feasibility of using two reconstructed milk products (RMP) as economical replacements for NDM in fortifying 2% lowfat milk for yogurt. These RMP's were spray dried blends_ of _whey proteins and caseinates. A second objective was to determine if concomitantly, partial enzymatic hydrolysis of lactose would afford the · same degree of sweetness in yogurts containing less sucrose than nonhydrolyzed yogurts. A yogurt with less sucrose should be attractive to consumers seeking products with fewer calories and one with lowered lactose levels would be more desirable to those deficient in lactase. Yogurts were manufactured with several concentrations of these variable factors and analyzed for composition. The yogurts were evaluated for flavor by a panel of dairy science faculty and by randomly selected volunteers in a consumer panel.

Library of Congress Subject Headings



Includes bibliographical references (pages 88-92)



Number of Pages



South Dakota State University


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Included in

Dairy Science Commons