Yogurt fermentation

Soymilk resembles dairy milk in composition, so it can also be fermented by lactic acid producing bacteria to produce such products as sour soymilk and soy yogurt. Fermentation of soymilk offers not only a means of preserving soymilk but also a possibility for modifying or improving its flavor and texture so that it becomes more acceptable to Westerners. It also leads to new types of soy products, which resemble cultured dairy products but are at a low cost. 

Nagai, T., Makino, S., Ikegami, S., Itoh, H., Yamada, H. (2011). Effects of oral administration of yogurt fermented with Icictobacillus delbrueckii ssp. bulgaricus OLL1073R-1 and its exopolysaccharides against influenza virus infection in mice. International Immunopharmacol-ogy, 11(12), 2246-2250. 

Singh M, Kim S. 2009. Yogurt fermentation in the presence of starch-lipid composite. J Food Sci 74(2) C85-C89. 

Cells of microorganisms have constituted a portion of human food siace ancient times. Yeast-leavened baked products contain the residual nutrients from the yeast cells destroyed duriag bakiag (see Bakery processes and leavening agents). Cultured dairy products, such as yogurt, buttermilk, and sour cream, contain up to lO cells of lactic acid bacteria per gram (19) (see Milk and milkproducts). Other examples of fermented foods consumed siace early times iaclude fermented meats, fish, and soybean products. 

Urethane [51-79-6] (ethyl carbamate) occurs as a natural by-product in fermented products such as wine, Hquors, yogurt, beer, bread, oHves, cheeses, and soy sauces. Whereas urethane has a known cancer etiology in experimental animals, no such relationship has yet been proven in humans (108,109). Alcohol may act by blocking the metaboHsm of urethane, and thus exert a protective effect in humans consuming alcohoHc beverages (110). 

Lactic Acid B cteri. The lactic acid bacteria are ubiquitous in nature from plant surfaces to gastrointestinal tracts of many animals. These gram-positive facultative anaerobes convert carbohydrates (qv) to lactic acid and are used extensively in the food industry, for example, for the production of yogurt, cheese, sour dough bread, etc. The sour aromatic flavor imparted upon fermentation appears to be a desirable food trait. In addition, certain species produce a variety of antibiotics. 

Lactic acid [50-21-5] (2-hydroxypropanoic acid), CH CHOHCOOH, is the most widely occurring hydroxycarboxylic acid and thus is the principal topic of this article. It was first discovered ia 1780 by the Swedish chemist Scheele. Lactic acid is a naturally occurring organic acid that can be produced by fermentation or chemical synthesis. It is present ia many foods both naturally or as a product of in situ microbial fermentation, as ia sauerkraut, yogurt, buttermilk, sourdough breads, and many other fermented foods. Lactic acid is also a principal metaboHc iatermediate ia most living organisms, from anaerobic prokaryotes to humans. 

Yogurt. Yogurt is a fermented milk product that is rapidly increasing in consumption in the United States. Milk is fermented with Uactobacillus bulgaricus and Streptococcus thermophilous organisms that produce lactic acid. Usually some cream or nonfat dried milk is added to the milk in order to obtain a heavy-bodied product. 

Ethyl carbamate, C2HyN02, is developed naturally during the fermentation of alcohoHc beverages. It also appears in foods such as bread and yogurt. Since ethyl carbamate is not easily distilled, its formation most likely involves a distillable precursor. The mechanism of ethyl carbamate formation probably involves cyanate produced from the oxidation of cyanide or from urea-based compounds in the beer. Cyanate reacts with alcohol to form ethyl carbamate as follows ... 

Lactose is mainly used as a fermentation substrate for lactic acid bacteria in dairy products, such as yogurt and cheese. These bacteria break down lactose into lactic acid, which solidifies the milk, and creates an acid environment that favors the benign lactic acid bacteria over those that are more harmful. 

To ensure the safety of food products, representative samples must be inspected so that foodborne bacteria can be identified.15,18,19 Bacteria producing heat-stable enterotoxins, such as Staphylococcus aureus, may be identified by biochemical and serological techniques.20,21 Molecular methods are now widely used for the identification of many pathogenic foodborne bacteria,15,22,23 In addition bacteria used as starter cultures for cheese, yogurt, other fermented foods and beverages, and probiotic dietary supplements may be identified for quality assurance.22,24,25... 

Antibiotics in milk can affect dramatically the production of fermented dairy products such as cheese, yogurt, buttermilk and sour cream. Routine application of antibiotic test kits such as the Delvo kit are required to avoid major losses on the line. 

Apart from public health impacts, residual antimicrobials in animal products can bring about technoeconomic losses in the food processing industry. It has long been known that the presence of some antimicrobial compounds in milk can dramatically affect the production of fermented dairy products such as yogurt, cheese, buttermilk and sour cream (72, 73). As shown in Table 10.2, even minute concentrations of antibiotics in milk can cause inhibition of the growth of commonly used dairy starter cultures (74). 

The hypothesis that dairy foods contain a cholesterol-lowering milk factor evolved from the observation that Maasai tribesmen of East Africa have low serum concentrations of cholesterol and a low incidence of cardiovascular disease in spite of their consumption of 4 to 5 liters/day of fermented whole milk (Mann and Spoerry 1974). Subsequently, sufficient amounts of yogurt, as well as unfermented milk (whole, lowfat, skim), were reported to exhibit a hypocholesterolemic effect both in humans and in laboratory animals in several studies (Mann 1977 Howard and Marks 1977, 1979 Nair and Mann 1977 Kritchevsky et al 1979 Richardson 1978 Hussi etal. 1981). However, not all investigators have observed a hypocholesterolemic effect of milk. This inconsistency may be explained in part by differences in the experimental design and in the specific type of dairy food used by investigators. 

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