Exploring the mechanism of milk kefir grain fermentation to improve the palatability of chokeberry juice

Chokeberry is a rich source of nutrients and bioactive compounds. Nevertheless, it is not popularly consumed due to its strong astringency and bitterness. The objective of this study was to improve the palatability of chokeberry juice through fermentation with milk kefir grains (MKG). The study also sought to examine the changes in physicochemical properties, sensory scores, microbial compositions, and volatile and non-volatile compounds of chokeberry juice during MKG fermentation (0, 24 and 48 h). The results demonstrated that an increase in total phenols and total antioxidant activities (DPPH, FRAP, ABTS), and a decrease in polymeric proanthocyanidins, induced by Acetobacter, Lactobacillus and Kazachstania, led to a fermented juice (48 h) with lower astringency and bitterness compared with the non-fermented one (0 h). Furthermore, the gas chromatography-mass spectrometry (GC-MS) analysis demonstrated that the MKG fermentation led to improvements in the levels of alcohols, acids and esters, while concomitantly reducing the concentrations of benzaldehyde and methylene chloride. The LC/ MS-based untargeted metabolomics analysis revealed notable increases in the relative levels of various compounds with small-molecular weights in the fermented juice, including polyphenols, organic acids and aldehydes. These findings indicate that MKG fermentation is a promising technique for enhancing the overall acceptability of chokeberry juice.