Evaluation of the Preservative Potentials of Lactic Acid Bacteria Isolated from Goat Milk and Finger Millet on Yoghurt

Abstract

Food fermentation using microorganisms is one the oldest technique for food production and preservation. Storage life can be extended with enhanced safety using the natural microflora and their antimicrobial products such as bacteriocins. The preservative potentials of bacteriocins extracted from lactic acid bacteria isolated from fresh goat milk and finger millet were studied. The isolated organisms  were identified based on their morphological, biochemical and physiological characteristics. Isolates were screened for their ability to produce bacteriocin using chloroform extraction method. Isolates with good bacteriocin yield were subsequently identified molecularly. The stability of the bacteriocins extracted was evaluated at varying temperature (30°C - 100°C) and pH (2 - 8) conditions. Also, the antimicrobial activities of the isolated LAB were tested against selected food-borne pathogens using the agar well diffusion method. Yoghurt was produced using the organism with the most potent bacteriocin extracts after which for the  effect of the bacteriocin extract on the yoghurt quality was assesed. Results indicated that LAB isolates with high bacteriocin producing potential based on their antimicrobial activity were identified as Lactobacillus plantarum, Enterococcus faecium, and Lactobacillus acidophilus. The LAB isolates produced bacteriocin with a broad spectrum antibacterial activity against some food-borne pathogens namely E.coli, S. aureus, S. typhi, Klebsiella sp. and P. aeruginosa with inhibition zones ranging from 18 to 28 mm,  Lactobacillus plantarum being most effective had a zone of inbition of …. against Salmonella typhimurium. The extracts were stable at temperatures of 30 - 80°C (>70%)  and pH range of 2.0 to 6.0 (> 50%). All bacteriocin extracts maintained the proximate composition of yoghurt and extended the shelf life up to 35 days. The result of the sensory evaluation showed preference for yoghurt preserved with the extract acidocin, obtained from Lactobacillus acidophilus The findings from this study showed that finger millet and goat milk are rich sources of lactic acid bacteria with good bacteriocin producing potential. which were able to preserve the yoghurt for a period of 35 days at a temperature of 4°C.