Production of Benzoic Acid in Fermented Goat's and Sheep's Milk

The production of goat’s and sheep’s milk in the Czech Republic has had a growing tendency in recent years, primarily on private farms. Here most of the milk is processed into fermented dairy products. These products show high digestive, nutritive, and organoleptic properties (J e n n e s , 1980; S l a c a n a c et al., 2010). Minor components of milk are also organic acids, which can be obtained from hydrolysis of milk fat. The organic acid content of milk depends on a variety of factors such as animal breed diet and duration of the lactation period. Some organic acids including hippuric and benzoic acids can reflect the health condition of the animals yielding the milk and they are present in varying quantities (B u i a r e l l i et al., 2003). Although cow’s milk contains only a few mg per kg of benzoic acid, fermented dairy products such as yoghurt and cheese can contain up to 50 mg kg–1 benzoic acid with most mean values around 20 mg kg–1 (S i e b e r et al., 1995). According to N i s h i m o t o et al. (1968, 1969) lactic acid bacteria convert hippuric acid present in milk to benzoic acid (Fig. 1) so that the latter could also be considered as a natural component of milk and dairy products. The level of benzoic acid depends primarily on the level of hippuric acid in raw milks and may also depend on the process of dairy product manufacture, especially on the used microorganisms (H e j t m a n k o v a et al., 2000a). In addition, Lactococcus lactis, Lactobacilus casei, Streptococcus thermophiles, Lactobacillus helvetius, Escherichia coli and Pseudomonas fluorescens can synthesize benzoic acid in milk (S a j k o et al., 1984; G a r m i e n e et al., 2010). According to S i e b e r et al. (1995) another possibility of benzoic acid forming is auto-oxidation of benzaldehyde and phenylalanine degradation. This substance is often identified in fermented dairy products and it is produced by bacteria of milk fermentation. Another way to enhance the content PRODUCTION OF BENZOIC ACID IN FERMENTED GOAT’S AND SHEEP’S MILK*