Biochemical characterization and antibacterial potential of lactic acid bacteria from Idli batter and their influences on properties of batter

Abstract

Idli is one of the flour-based foods fermented by lactic acid bacteria. This study was designed to characterize the lactic acid bacteria isolated from Idli batter and to determine their antibacterial activity. Physicochemical changes of batter during fermentation and sensory qualities of the final product (Idli) also were determined. Lactic acid bacteria were isolated from Idli batter and characterized up to genus level. Agar well diffusion assay was used to determine the antibacterial activity of isolates against foodborne pathogens (Salmonella enterica, Escherichia coli and Staphylococcus aureus). Changes of pH, lactic acid bacterial count, titratable acidity of batter during fermentation and sensory properties of the final product were measured. Ten isolates (I-1 to I-10) were isolated from Idli batter, of which, six were rod and other four were cocci shaped. All ten isolates were Gram positive, non-motile, non-spore formers and catalase activity negative. It was confirmed that all isolates belong to lactic acid bacteria up to genus level. Based on diameter of the inhibition zone, among ten isolates, I-6 was considered as the highest potential bacteriocinogenic isolate. Inhibition zone diameter of isolates ranged 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% throughout the fermentation period (0-32 h). With fermentation, the lactic acid bacterial count was increased, and highest lactic acid bacterial count of 9.88 log10cfu/g was observed after 12 h of fermentation. Idli prepared from Idli batter after 8-12 h of fermentation scored maximum for the sensory quality. From this study it is concluded that all lactic acid bacteria isolates possess antimicrobial activity and physicochemical and sensory qualities of Idli batter changed with duration of fermentation.