Comprehensive metabolomics based exploration of in vitro digestive characteristics of Lacticaseibacillus rhamnosus biotransformed apple polyphenols

Apple ( Malus domestica ) polyphenols possess functional properties; however, their human body absorption is impeded. To enhance their absorption, apple polyphenols were fermented using Lacticaseibacillus rhamnosus zrx01. Gastrointestinal digestion and metabolomics analyses were conducted. The results showed that the polyphenol content decreased significantly to 1.12 mg/mL ( p < 0.05) in fermentation group and increased to 2.01 mg/mL in non-fermentation group; 6 differential metabolites such as ferulic acid (log₂ FC = -3.28) and p-hydroxybenzoic acid (log 2 FC = -2.80) were identified by metabolomics, among which epicatechin (VIP = 2.54) and chlorogenic acid (VIP = 2.40) were significantly increased. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that differential metabolites were significantly enriched in 10 metabolic pathways, including phosphatidylinositol 3 kinase-protein kinase signaling pathway ( p = 0.00029), fluid shear stress, and atherosclerosis pathway ( p = 0.00327). The research shows fermentation converts macromolecular polyphenols into small molecules via deglycosylation, altering postdigestive metabolite profiles and providing evidence for bioavailability mechanisms and functional development of apple polyphenols.