Biosynthesis of Antimicrobial Compounds by Lactic Acid Bacteria and Its Use as Biopreservative in Pineapple Juice

Lactic Acid Bacteria (LAB) are able to synthesize antimicrobial compounds which have both functional and technological properties in foods. This ability of LAB can be explored for use as bio-preservative in food. This study aims at identifying LAB isolated from fresh milk and employing it as natural preservative in extending the shelf life of Pineapple juice. Twenty strains of LAB were isolated from fresh milk and were identified as L. fermentum, L. plantarum and L. lactis respectively . L. fermentum produced the highest antimicrobial compound Lactic acid, diacetyl and hydrogen peroxide (1.8, 0.15, 0.03 g/l) respectively and the least was produced by L . lactis (1.2, 0.10, 0.02 g/l) respectively. Samples were pasteurized at 85°C for 15mins after which lactic cultures were introduced to the fresh pineapple juice singly and in combination. The shelf life and microbial load of the inoculated samples and control without the lactic cultures were monitored at room temperature for 7 days. LAB count in the inoculated samples increased from 3.1x10 3 - 8.2x10 6 cfu/ml from day 0 to 5 with no LAB growth noticed in the control. Yeast and Coliform Count increased after day 5 to (5.1x10 4 and 2.3x10 3 cfu/ml respectively) but for control increased to 6.3x10 5 and 5.2x10 4 respectively. Aerobic plate count increased to 3.0x10 4 cfu/ml after day 5 and 7.4x10 5 for control. A decrease was observed in LAB count after day 5 to 3.2x10 5 cfu/ml. Lactic cultures extended the shelf life of Pineapple juice for 5 days after which there was deterioration monitored by increased count and decreased LAB activity. LAB exhibited a high antimicrobial effect on food borne contaminants. This ability of LAB can be employed as biopreservatives against food pathogens which also help to maintain and preserve the nutritive qualities of pineapple juice for an extended shelf life.