Development of a Mixed-Strain Fermentation Process for Sour Pomegranate: An Analysis of Metabolites and Flavor Compounds

Sour pomegranate, a distinctive product of Xinjiang, China, is characterized by its sour and astringent taste, which contributes to a low processing rate. This study utilized single-factor experiments to screen three strains: Lactobacillus fermentum, Lactobacillus plantarum, and Lactobacillus acidophilus. Through uniform design experiments, the mixed-strain ratio of L. fermentum:L. plantarum:L. acidophilus = 45%:31%:28% was determined. In addition, the amount of mixed inoculum was 2%, and the fermentation time was 11 h. Additionally, a mixed inoculation amount of 2% and a fermentation duration of 11 h were established. Utilizing electronic nose, electronic tongue, gas chromatography–ion mobility spectrometry, and non-targeted metabolomics, comparative analyses were conducted on the flavors and metabolites pre- and post-fermentation. The findings indicated that post-fermentation, umami increased by 32%, richness was enhanced by 6%, and the positive aftertaste was significantly extended. Mixed-strain fermentation facilitated the enrichment of alkanes, alcohols, aldehydes, and terpene volatile compounds; notably, the content of hexanal (fresh fruity aroma) and limonene (citrus aroma) increased by 1.95 times and 1.45 times, respectively, thereby augmenting the complexity of the aroma. Furthermore, mixed-strain fermentation significantly upregulated terpenes, amino acids and their derivatives, steroids and their derivatives, and alkaloid metabolites. These results offer potential technical support for the high-value utilization of agricultural products.