Bio-preservative effect of lactic acid bacteria isolated from fermented cow milk on nunu

Purpose: The role of lactic acid bacteria (LAB) in food fermentation cannot be over emphasized. LAB being generally regarded as safe (GRAS) have certain functional properties that enhance its suitability as bio-preservatives. During fermentation of foods they are capable liberating certain metabolites that may be inhibitory or lethal to other microorganisms in the fermenting medium. In this regards, this study focused on the functional properties of LAB as bio-preservative for nunu production. Method: The lactic acid bacteria used in this work were isolated from fermented cow milk and were screened for their inhibitory effect, out of seven identified; Result: only four LAB strains were capable of this effect (Lactobacillus pentosus, L. plantarum, L. fermentum and L. plantarumB3). L. pentosus had the highest inhibitory zone which ranged from 11 mm to 12 mm on Bacillus cereus, Pseudomonas aeruginosa and Staphylococcus aureus, while the least inhibitory zone was produced by L. fermentum. L. pentosus acidified fermented cow milk within 18 hr of fermentation reducing acidity from 0-3.86 than other strains of LAB isolates. The proteolytic screening of LAB isolates revealed that L. pentosus had the highest zone (18 mm) while L. fermentum had the least proteolysis (12 mm) with no lipolysis. Conclusion: Nunu fermented with mixed culture of L. plantarum B3 and L. pentosus as well as single starter culture of L pentosus had better shelf life and kept for 5 days before spoilage occurred relative to 3 days observed for spontaneously fermented nunu.