Abstract
Exopolysaccharides synthesized by lactic acid bacteria play a major role in the manufacturing of fermented dairy products as thickening agents. Exploration of the biodiversity of wild lactic acid bacteria from natural environments is currently the most suitable approach to search for the desired exopolysaccharide-phenotype. A total of 82 thermophilic lactic acid bacteria strains were isolated from Algerian raw camel milk. The isolation of strains was carried on modified Chalmers agar medium, under semi anaerobic conditions at 42°C. Bacterial isolates were phenotypically characterized and grouped into four genera: Lactobacillus (31.7%), Enterococcus (30.5%), Streptococcus (24.4%) and Pediococcus (13.4%). Based on the mucous type of the colonies, thirty EPS-positive strains were selected to be screened for their ability to produce exopolysaccharides. The production of polymers was carried out on Man, Rogosa and Sharpe (MRS) broth, supplemented with lactose and glucose as carbon sources. Yields quantification of soluble exopolysaccharides using a colorimetric method, showed that the selected strains produce yields ranging between 160 and 740 mg/l for Lactobacillus strains, between 126 and 319 mg/l for Streptococcus strains, between 70 and 242 mg/l for Enterococcus strains and between 132 and 134 mg/l for Pediococcus strains. This suggests that some strains have potential to be used as new culture starters for this and possibility other dairy products. Key words: Camel milk, thermophilic lactic acid bacteria, exopolysaccharides.
Highlights
Microbial polysaccharides have been investigated in detail during the last few decades
The dairy lactic acid bacteria (LAB) used in the manufacture of fermented milks such as Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus and Lactococcus lactis subsp. cremoris were extensively studied in the last years (Cerning, 1995)
The EPS-yields of TLAB strains have shown moderate correlation with the bacterial growth, but, they were low in correlation with values of total sugar fraction. We suggest that this correlation is not necessary because the bacterial EPS may contain a non-carbohydrate moiety. These findings shows that fermented camel milk can be a potential source of thermophilic lactic acid bacteria that produce exopolysaccharides
Summary
Microbial polysaccharides have been investigated in detail during the last few decades. There is an increasing demand in food industries for live microbes producing polysaccharides (Patel et al, 2010). Bacterial polysaccharides can be divided into intracellular polymers, structural polymers and extracellular polymers or exopolysaccharides (EPS) (Kumar et al, 2007). The bacterial EPS vary greatly in their composition and in their chemical and physical properties (Sutherland, 1999). Many lactic acid bacteria (LAB) are able to produce EPS. The dairy LAB used in the manufacture of fermented milks such as Streptococcus thermophilus, Lactobacillus delbrueckii subsp. EPS synthesized by LAB play a major role in the manufacturing of fermented dairy products (Duboc and Mollet, 2001; Jolly et al, 2002)
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