Isolation and characterization of lactic acid bacteria from yogurt samples and evaluation of their fermentation efficiency

Abstract

Lactic acid bacteria (LAB) are essential microorganisms in the manufacture of dairy products because they produce lactic acid, a well-known preservative, are used in food fermentation and can have probiotic properties. The present study was designed to isolate and characterise LAB from the local samples of yogurt and compare its fermentation efficiency in milk. Five samples of yogurt (A-E) were taken from various places of Bangladesh and cultured by serial dilution technique on MRS agar. Selected isolates were purified in MRS slants in an anaerobic candle-jar and transferred to pasteurized milk. The pH, liquid volume and dry yogurt weight were used to measure fermentation performance. Sample D was the most successful in colony growth, slant culture development and yogurt formation. The pH of fermented milk samples was in the range 3.98-4.19, showing an effective acidification. The mean dry weight of the yogurt was between 54.68 to 71.11 g and liquid was between 50.25 to 68.25 mL. The optimal performance in fermentation was achieved with the application of 200–300 μL of the starter culture per 150 mL of milk, which corresponds to about 0.13–0.20% (v/v).The results indicate that the yogurt may be a good source of LAB that can be used in the dairy, food preservation, probiotics and pharmaceutical research.