Functional and sensory enhancement of cucumber juice by RSM-optimized Lactobacillus rhamnosus NCDC-347 fermentation

The present study aimed to develop a fermented cucumber juice beverage using Lactobacillus rhamnosus NCDC-347. The fermentation procedure was optimized using Response Surface Methodology (RSM). The independent variables used for optimization were inoculum size (2-5%), pH (5-9), and incubation temperature (30-45 °C), while the responses were Total Phenolic Content (TPC), antioxidant activity, total sugar content and microbial growth. The optimized fermentation conditions were 37.5 °C, pH 7.0, and an inoculum size of 3.5%. Under these conditions, L. rhamnosus NCDC-347 reached approximately 8.0 ± 0.1 Log CFU/mL after 48 h of fermentation. Under the optimized conditions, fermentation significantly reduced the pH from 7.00 ± 00 to 3.29 ± 0.13, and total soluble solids 3.3 ± 0.15 to 1.2 ± 0.05, along with a reduction in total sugar content from 17.94 ± 1.10 g/L to 4.40 ± 0.45 g/L, confirming effective microbial metabolism. A significant increase in TPC from 1.02 ± 0.06 g GAE/L, to 1.5 ± 0.06 g GAE/L was observed which was associated with enhanced antioxidant activity as determined by DPPH (80.79 ± 1.81%), and ABTS (93.43 ± 0.90%) radical scavenging assays. The fermented cucumber juice showed significant inhibitory activity against α-glucosidase (41.66 ± 1.52%), and α-amylase (57.33 ± 2.51%), indicating potential α-amylase and α-glucosidase inhibitory activity in vitro. Gas chromatography-mass spectrometry (GC-MS) was employed for the volatile profiling of fermented and unfermented cucumber juice, which revealed the production of several fermentation-derived compounds. Cell free supernatant of cucumber juice exhibited antimicrobial activity with highest and lowest inhibition against Bacillus subtilis MTCC 441 (16 mm), and pseudomonas aeruginosa ATCC 15692 (09 mm) respectively. The fermented cucumber juice showed cytotoxic activity against MCF-7 cells under the tested conditions. Sensory assessment using a 7-point hedonic scale showed higher mean scores for most evaluated attributes in the fermented juice than in the unfermented juice.