Bioprocess optimization and functional properties of cucumber juice fermented with Lacticaseibacillus casei NCDC-17: from physicochemical changes to health -promoting-effects

A vegetable-based probiotic drink provides an alternative to dairy products for delivering beneficial microorganisms. This study was conducted to develop a fermented probiotic drink using cucumber juice. The probiotic starter culture used was Lacticaseibacillus casei NCDC-17. The fermentation process was optimized to enhance antioxidant activity, total phenolic content, and microbial viability. A rotatable central composite design using response surface methodology was used to set up the experimental design. The independent variables for the optimization were incubation temperature (30-45 °C), pH (5-9), and inoculum size (2-5%). The optimal fermentation conditions were observed to be incubation temperature 37.5 °C, pH 7, and inoculum size 3.5%. The results showed that the pH, total soluble solids, total flavonoids, and total sugar content were decreased after the fermentation. It was observed that the total phenolic content, and antioxidant activity were increased to a significant level after the fermentation. Results revealed that the fermented drink inhibits the key enzymes (alpha-amylase, and alpha-glucosidase) related to diabetes. The volatile compounds were identified using Gas Chromatography-Mass Spectrometry. A total of 54 distinct volatile compounds were identified following the fermentation process, indicating significant biochemical transformation and metabolic activity of the microbial culture. Cell-free supernatant of the drink exhibited antimicrobial activity with the highest and lowest inhibition against Escherichia coli (14 mm), and Staphylococcus aureus (11 mm), respectively. The fermented sample was evaluated for its cytotoxic potential against MCF-7 human breast cancer cell lines. The fermented sample exhibited marked growth inhibitory effects, against MCF-7 cell lines. Sensory evaluation was performed using a 7-point hedonic scale to evaluate attributes such as appearance and colour, mouth feel, aroma and flavor, taste, and overall acceptability. Results showed that the probiotic drink was well accepted.