Production of acidified cow- and soy-milk with antimicrobial properties using lactic acid bacteria from indigenous fermented foods

Indigenous fermented milk in most West African countries including Nigeria is produced by spontaneous fermentation which results in products lacking uniformity, predictability, and safety. In this study, lactic acid bacteria (LAB) with antimicrobial properties from indigenous fermented foods were investigated for use as fermenting organisms for the acidification of cow and soy milk products. Twenty-two LAB isolates inhibited test organisms with diameter clear zones ranging from 3.67 to 28.00 mm. Lactobacillus fermentum (pH 4.46, 27.00 mm), L. acidophilus (pH 3.38, 28.00 mm), L. plantarum (pH 4.24, 25.67 mm), and L. coryniformis (pH 4.70, 23.33) with highest acidifying properties and inhibitory zones respectively, significantly impacted the sensory and proximate quality of the milk samples after fermentation. The texture of all the milk samples was altered through the appearance of curds and the beany aroma of soy milk was significantly suppressed. However, there was no significant change in the colour of the fermented milk compared to the original milk samples. Respectively for the cow and soy milk samples, the crude fibre (14%, 21%) and ash contents (27.36%, 56.04%) were depleted due to fermentation, while lipids (11.03%, 7.79%) and proteins (18.28%, 25.48%) were significantly improved. Optima acidification was obtained at 30 °C and 40 °C. The study concluded that the LAB isolated from Nigeria's indigenous foods has antimicrobial and acidifying properties and can be used to produce quality fermented milk. The study recommends a detailed optimization of the fermentation parameters and a comprehensive analysis of the antimicrobial substances and other metabolites of value that may be produced by the isolated LAB.