Fermentation of tomato and carrot juices was carried out with a native isolate of Lysinibacillus sphaericus. Initial screening showed that total phenolics, antioxidants and titratable acidity were higher in both the fermented juices than respective un-fermented controls. Better fermentation characteristics were found in fermented tomato juice at 37ºC (pH 5.8, TA% 0.38 and cell viability of 7.8 x 107 CFU/mL) than those of fermented carrot juice (pH 5.5, TA% 0.30 and cell viability of 6.9 x 107 CFU/mL). Hence, fermentation of tomato juice was optimized by Central Composite Design using temperature, pH, incubation time and sucrose concentrations as critical parameters. The optimized conditions for fermentation of tomato juice were determined to be pH 6.2, temperature of 37ºC, inoculum size of 7.58 log CFU/mL, sucrose concentration of 10% and fermentation for 24 h. The antimicrobial activity of the fermented tomato juice against Bacillus cereus MTCC 7190 was better (inhibition zone of 10 mm) than the fermented carrot juice (8 mm). The cell viability of Lys. sphericus at 4ºC for 6 weeks was better in tomato juice (0.9 x 106) than in the carrot juice (0.6 x106 CFU/mL). Fermented juices exhibited good sensory attributes and could possibly be used as probiotic drinks.
Key words: Tomato and Carrot juices, Lysinibacillus sphaericus, Fermentation, Response surface methodology, Antimicrobial activity
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