Impact of partial and total replacement of milk by water-soluble soybean extract on fermentation and growth parameters of kefir microorganisms

In this study, the use of soybean extract on production and physicochemical characteristics of kefir was assessed. Also, the growth parameters of yeasts and lactic acid bacteria (LAB) during fermentation were evaluated. Experiments were carried out combining water-soluble soybean extract (S) and milk (M), leading to the evaluation of total or partial replacement of milk (formulations 100%S, 50%S50%M) a control formulation (100%M). During kefir fermentation, physicochemical analysis carried out as well as enumeration of yeasts and LAB. In all formulations, lactic acid concentration increased due to carbohydrates consumption by kefir microorganisms resulting in decrease of soluble solids content and increase of acidity. The final acidity of beverages varied from 0.600 to 0.738 g of lactic acid/100 mL and soluble solids ranged from 6.40 to 5.67 °Brix. Formulations 100%S and 100%M presented LAB counts of 8 log10 CFU/mL. LAB lag time increased in formulation 50%S50%M compared to formulations 100%S and 100%M (2.20 h, 1.03 h and 1.06 h, respectively). LAB and yeasts growth parameters were not affected in beverages prepared with milk and soybean kefir. This is the first study that examined the yeast and LAB growth parameters using water-soluble soybean extract fermented with kefir.