Isolation of Lactic Acid Bacteria from Idli Batter and Assessing their Antibacterial Potential

Abstract

Idli is one of the flour-based fermented foods that can potentially contain probiotic lactic acid bacteria. This study was designed to isolate and determine antibacterial activity of lactic acid bacteria from Idli batter, identify the acidity changes of Idli batter and sensory quality changes of Idli with fermentation time up to 32 h. Lactic acid bacteria were isolated from Idli batter and characterized to genus level by biochemical tests. Agar well diffusion assay was carried out to determine the antibacterial activity of isolates against food borne pathogens; Salmonella enterica, Escherichia coli and Staphylococcus aureus. With fermentation, changes of pH, Lactic acid bacterial count, titratable acidity and sensory quality of final product were measured. In overall, ten isolates were recognized from Idli batter, of which, six were rod shaped, Gram positive, non-motile, non-spore formers and negative to catalase activity, belonging to Lactobacillus spp. Other 4 isolates were cocci shaped, Gram positive, non-motile, non-spore formers and negative to catalase activity, belonging to Lactococcus spp. On the basis of zone of inhibition, among ten isolates, isolate I-6 was considered as the highest potential bacteriocinogenic isolate against all test organisms. The overall zone of inhibition diameter of isolates fell within range from 7.3±1.53 to 16.3±0.58 mm. The pH dropped steadily from 6.28 to 3.72, while titratable, acidity increased from 0.24% to 0.92% during the period of 0 to 32 h. With fermentation time, the lactic acid bacterial count was increased and higher lactic acid bacterial count of 9.88 log10 cfu/g was observed after 12h of fermentation and the count was reduced with increasing acidity. Idli prepared from idli batter after 8-12 h of fermentation scored maximum for the sensory quality. Lactobacilli spp are the predominant Lactic acid microbial group involved in natural Idli batter fermentation which have anti-microbial activity against food pathogens.