Immobilisation of Lactic Acid Bacteria and Application of Bacteriocin for Preservation of Fruit Juices

Lactic acid bacteria are generally recognised as safe (GRAS) organisms producing bacteriocins that help in inhibiting food borne pathogens. However, its narrow spectrum activity is a major limitation for food applications. Thus, a combination of different methods were attempted to broaden the antimicrobial spectrum of bacteriocins produced using lactic acid bacteria. Initially, the antimicrobial activity of bacteriocin from various combinations of mixed lactic acid bacteria and single culture were determined after 56 h at 35 °C to select the desirable combination with maximum antimicrobial activity. Combination of bacteriocin produced by Lactobacillus plantarum DFR4, Enterococcus faecalis DFR4 and E. faecalis DFRP1showed maximum activity against Listeria monocytogenes with zone of 31.24±0.33 mm in agar disc diffusion assay. The specific activity and purification of bacteriocins produced by these isolates were found to be highest in gel permeation chromatography where as, the yield was highest in 80 percent acetone precipitation. The partially purified bacteriocins were further investigated for the effect of pH, enzymes and temperature stability and were found to be thermo stable and active at pH range of 3 to 5. Proteolytic enzymes such as protease and papain inactived the bacteriocins while amylase had no inhibitory effect. The antimicrobial activity of bacteriocin produced from bamboo (Bambusa vulgaris) fibre immobilised Lactobacillus plantarum DFR4 was found to be more (zone size=20.91±0.35 mm) in comparison to free cells (zone size=8.52±0.26 mm) after 24 h of incubation at 37 °C. Further, immobilisation of Lactobacillus plantarum DFR4, Enterococcus faecalis DFR4 and E. Faecalis DFRP1 using bamboo fibre aided in faster production of bacteriocins in 24 h. Mosambi juice (Citrus limetta) supplemented with bacteriocins (produced from mixed bacterial isolates) had a shelf life of 26 days at 5 °C.