Sour Milk Products, Yoghurt

Metabolic products of lactic acid bacteria, such as diacetyl, ethanal, dimethylsulfide, acetic acid and lactic acid contribute to this aroma. Carbon dioxide also appears to be inqtortant. In good 

Only the three compounds listed in Table 10.40 make an appreciable contribution to the aroma of butter. A comparison of the aroma profiles of five samples of butter (Table 10.41) with the results of a quantitative analysis (Table 10.40) show that 

3 Sour cream Slightly buttery, mild, sour 1-2 

4 Sour cream Rancid, like butyric acid 3 

Rancid, soapy aroma defects, which occur in butter samples with very low concentrations of free fatty acids, can be due to contamination with anionic detergents (sodium dodecyl sulfate, sodium dodecyl benzosulfonate). Detergents of this type are used to disinfect the udder and the milking machine. 

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Sour milk products are always cultured dairy products with lactic acid bacteria (depending on the food legislation of the respective country). After increasing the dry matter, pasteurisation and incubation of culture, they are processed into yoghurts of set, stirred or drinking consistency, with or without a final heat treatment. 

Since pectin can set into a gel, it is widely used in marmalade and jelly production. Standard conditions to form a stable gel are, for instance pectin content <1%, sucrose 58-75% and pH 2.8-3.5. In low-sugar products, low-ester pectin is used in the presence of Ca + ions. Pectin is also used to stabilize soured milk beverages, yoghurts and ice creams. 

Migration of ethylbenzene Ifom polystyrene into various foods has been reported. The following ethylbenzene levels were found sour milk beverages, < 2.5-6 pg/L noodle soup, 15-21 pg/L noodle curry, 89-153 pg/kg and wantan soup 9-28 pg/L (ECETOC, 1986). Migration of ethylbenzene Ifom polystyrene containers into dairy products resulted in concentrations of ethylbenzene ranging from 2 to 4 pg/kg in yoghurt and 4 pg/kg for chocolate dessert (Ehret-Henry et al, 1994). 

Homofermentative lactic acid bacteria (such as Lactococcus lactis and Streptococcus lactis) produce (-l-)-L-lactic acid (e.g. in sour cream). Both isomers, (-l-)-L-lactic acid and (-)-D-lactic acid (8-65), are formed during milk fermentation by heterofermen-tative bacteria (lactic acid bacteria are mostly heterofermentative bacteria) and lactic acid thus also occurs as a racemate in sauerkraut, pickled cucumbers, olives and silage. For example, bacteria of the genus Leuconostoc produce d-lactic acid, while bacteria Pediococcus acidilactici and other bacteria produce racemic lactic acid. The content of lactic acid in dairy products is 0.5-1.0%. L-Lactic acid in yoghurt represents about 54% and in sour cream 96% of the total lactic acid content. The total lactic acid content in sauerkraut is 1.5 2.5%, in fermented cucumbers it ranges from 0.5 to 1.5% and fermented green olives contain 0.8 to 1.2% lactic acid. 

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