The flavor of yogurt depends on the milk, its heat-treatment, the starter strains used, the incubation temperature, and the balance of the organisms in the yogurt. Biochemically, flavor compounds of yogurt include but are not limited to lactic acid, acetic acid, formic acid, propionic acid, butyric acid, acetaldehyde, acetone, diacetyl, acetoin, and several other compounds. In milk, ST produces formic, acetic, propionic, butyric, isovaleric and caproic acid, diacetyl, acetone, and some acetaldehyde. Lactobacilli, on the other hand, produce large quantity of lactic acid, acetaldehyde, diacetyl, peptides, and amino acids. Many of the compounds are derived from lactose and some from other components in milk (22). The flavor of yogurt can turn acidic and bitter during storage throughout shelf life. Protein degradation can continue during cold storage of yogurt and some peptides released may be bitter (22,61). Incubation temperature of yogurt below 30°C may also cause bitterness (61). It is again emphasized that the cultures used should be carefully selected to deliver quality attributes of yogurt throughout its shelf life.
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