Lactic acid fermentation of vegetables could be a good alternative solution for extending their shelf-life and adding value. However, lactic acid bacteria (LAB) are diverse, with variable metabolic activities during fermentation, which leads to the production of different metabolites that can be important for consumer acceptance. The aim of this work was to study the impact of LAB metabolism on volatile organic compounds (VOCs) during cucumber fermentation. Among 161 LAB isolated from Cambodian fermented vegetables, five LAB species including Lactiplantibacillus plantarum, Lactiplantibacillus pentosus, Lactococcus lactis, Limosilactobacillus fermentum, and Pediococcus pentosaceus were selected to ferment mashed cucumbers by single inoculation for 24 h. VOCs were analyzed by using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry. The results indicated that each LAB strain had an impact on the profile of these VOCs. For instance, aromatic compounds, likely coming from amino acid metabolism, were highly produced by both species of Lactiplantibacillus. However, these strains showed different behaviors regarding compounds derived from plant fatty acid metabolism. The concentration of aldehydes which was of 39.14 μg-4-nonanol-equivalent/kg in the plant, was increased to 66.03 μg/kg for L. plantarum, while L. pentosus produced the highest total semi-quantitative amount of saturated primary alcohol at 94.65 μg-4-nonanol-equivalent/kg. With 22 compounds, L. lactis generated more than twice as much different esters; while, with 21.80 and 18.24 μg-4-nonanol-equivalent/kg, respectively, L. fermentum and P. pentosaceus produced the highest level of acetic acid. As a heterofermentative LAB, L. fermentum might produce acetic acid via glucose metabolism, whereas P. pentosaceus, as homofermentative LAB, might synthesize acetic acid from other pathways. Our results showed that LAB present metabolic diversity with differences among species on mashed cucumbers as green vegetables.

Cryoprotectants are used to protect biological cells from damage caused by freezing. This study aimed to determine the effect of various types of cryoprotectant on the survival rate of freeze-dried Limosilactobacillus frumenti (L. frumenti) used as a starter culture for cucumber fermentation. Mixtures of freeze-dried L. frumenti with cryoprotectants were prepared using two different ratios (1:2 and 1:10). The survival rate of L. frumenti was determined by viable cell counts (CFU/mL) after freeze-drying, and fermentation performance was evaluated in terms of physicochemical quality and sensory evaluation. Skim milk proved to be the most effective cryoprotectant, yielding a survival rate of approximately 70% (70.07% for the 1:10 ratio and 70.01% for the 1:2 ratio) after 24 h of storage at 4 °C. Sensory evaluation indicated that cucumber fermentation prepared with freeze-dried L. frumenti mixed with skim milk (ratio 1:10) was the most preferred by panelists.