Biosynthesis of Enzymes in Fermented Foods by Lactic Acid Bacteria and Possible Use as Bio-Preservative in Fermented Milk

Abstract

This work focused on isolating Lactic Acid Bacteria from fermented local milk, assaying the enzymes produced by the organisms, using them as starters in the fermentation of fresh milk and monitoring their bio-preservative activities. Fresh milk samples pasteurized at 85°C for 15 min were inoculated with lactic cultures (3x106 cful/ml). Two organisms with high enzymatic activities were used as starters singly and in combination. LAB, yeast, coliform and aerobic count were monitored during fermentation at room temperature for five days. Twenty four LAB were isolated from replicate samples of locally fermented milk called Nunu. They were identified as L. plantarum, L. fermentum, L. lactis, L.bulgaricus, L. casei and L. brevis. The organisms were screened for the production of antimicrobials; hydrogen peroxide, diacetyl, lactic acid and Agar well diffusion method was used to monitor the antagonistic activities. These were used to screen the organisms and those with the best technological properties were selected as starters. Enzyme production and activities were monitored using Dinitrosalysilic acid method. Enzymes production; amylase, alpha-galactosidase, invertase and mellibiase ranged from 1.0-2.6 unit/ml from day 0-5 after which there was a significant reduction (0.5 unit/ml). Two organisms with high enzymatic activities; Lactobacillus acidophilus and L. plantarum were used as starters singly and in combination to inoculate the fresh milk samples which have been pasteurized earlier. The total LAB, yeast, coliform and aerobic count were monitored during fermentation at room temperature for five days. LAB count increased significantly from day 0-5 (5.1x108cfu/ml). A gradual increase was observed in yeast and aerobic count (3.6x103-6.1x104cfu/ml). LAB demonstrated high enzymatic and bio-preservative activities on fresh milk by preserving the nutritional qualities of the milk and extending the shelf life of fresh milk. It also acts as natural preservative in milk by inhibiting spoilage microorganisms.