Exo-polysaccharide (EPS) production by some lactic acid bacteria (starter) during fermentation could affect the physical properties of yoghurt. In this study, at first EPS content and its effects on physical properties of three traditional (S1, S2 and G) and one industrial (I) yoghurt samples were studied. The results showed that there was significant differences in fat content, solid non-fat content, pH, EPS content, viscosity, elasticity and sensitivity to syneresis among samples. Statistical analysis based on a completely randomized design revealed that a significant correlation exists between EPS content and viscosity as well as resistance to syneresis of the samples. Fat content and solid non-fat content of the samples showed no correlation with physical properties of the samples. In the second phase of the study, to remove effects of raw milk composition and to be able to attribute the results to the EPS producing activity of the starter, skim milk was used to produce yoghurt samples using yoghurt samples tested in the first stage only as sources of starter. In these yoghurt samples, there were significant differences between amount of EPS and physical properties of yoghurts. There was also a significant correlation between EPS content and physical properties of each sample.

Keywords: Exo-Polysaccharide (EPS), Yoghurt, Starter, Lactic Acid Bacteria, Physical properties

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