Effect of fermentation parameters and their optimization on the phytochemical properties of lactic-acid-fermented mulberry juice

Morus nigra is an excellent source of polyphenols which, are associated with its functional properties. Lactic acid bacteria have been reported to hydrolyse complex polyphenols into simpler and more bioactive compounds during fermentation. Fermentation process depends on multiple parameters to obtain a desired product. The study evaluated the effects of fermentation parameters [temperature (TF), pH, inoculum concentration (IC) and brix (°Bx) on the phytochemical properties of lactic-acid-fermented mulberry juice (LFMJ)]. Correlation analysis showed that quadratic polynomial model could be used to illustrate the influence of fermentation parameters on phytochemical properties of LFMJ. Response surface plots showed that these independent variables significantly influenced the phytochemical content of LFMJ. The outcome of the study demonstrated that lactic acid fermentation significantly impacted on the total phenolic, anthocyanin and flavonoid contents of the beverage. The optimum fermentation conditions to obtain the highest phenolic, anthocyanin and flavonoid contents were TF (40 °C), pH (4.0), IC (3.90% v/v) and °Bx 14. Under the above-mentioned conditions, the experimental results obtained [total phenolic content (928.12 ± 3.05 mg/100 ml), total anthocyanin content (131.85 ± 1.03 mg/100 ml) and total flavonoid content (440.50 ± 2.00 mg/100 ml)] were in line with the predicted values—total phenolic content (879.25 mg/100 ml), total anthocyanin content (128.99 mg/100 ml) and total flavonoid content (436.63 mg/100 ml)) and an overall desirability of 0.911. The LFMJ was found to have a significant (P < 0.05) better colour, aroma, flavour, taste and overall acceptability compared to the non-fermented mulberry (NFMJ).