Optimization of co-fermentation of carrot and tomato juices by probiotic bacteria and yeast using a central composite design

Abstract

In the present study, experiments were conducted on the suitability of tomato, carrot and mixed tomato+carrot juice for probiotication by Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus casei and Lysinibacillus sphaericus individually and in combination with a yeast (Saccharomyces boulardii). The combination of Lys. sphaericus and S. boulardii showed good results. Further optimization was carried out using a central composite design (CCD). The autoclaved juices were inoculated with probiotic cultures both alone or in combination with the yeast culture and incubated at 37°C for 72 h. After 24 h of fermentation, the pH levels had decreased from 6.1 to 4.0. Titratable acidity also increased from 0.12% to 0.36%, while the viable cell counts of probiotic bacteria and yeast gradually increased from 6.5 to 7.0 CFU/ml and from 5.4 to 7.9 CFU/ml, respectively. Subsequently, following further fermentation, viable cell counts decreased due to a decrease in pH and an increase in acidity as well as a lack of nutrients in the medium. The antimicrobial activity of mixed juice was found to have a maximum zone of inhibition of 11.8 mm and 9.8 mm against Pseudomonas aeruginosa MTCC 741 and Bacillus subtilis MTCC 2394, respectively. Probioticated tomato and carrot juices showed good sensory attributes.