Walnut Pellicle Polyphenols Trigger Lactiplantibacillus plantarum DX7 to Produce Indole-3-Lactic Acid

Indole-3-lactic acid (ILA), a gut microbial metabolite,
plays an
important role in gut health. However, the number of bacterial strains
that can produce ILA remains limited. This study investigated the
synergistic relationship between Lactiplantibacillus
plantarum DX7 and walnut pellicle polyphenols (WPP)
for enhancing ILA production. Genomic analysis confirmed that the
strain, though equipped with genes necessary for converting tryptophan
(Try) to ILA, did not produce ILA under the standard conditions. However,
cofermentation with WPP stimulated bacterial growth and ILA biosynthesis. L. plantarum DX7, in turn, modulated the WPP phenolic
profile and enhanced its antioxidant activity. Specific phenolic acids,
including ferulic, gallic, dihydrocaffeic, and cinnamic acids, were
identified as key WPP components stimulating bacterial growth and
activating the Try-to-ILA pathway. These results demonstrated a mutualistic
interaction where WPP activated the metabolic potential of L. plantarum DX7 for ILA production, while the bacterium
biotransformed WPP to improve its functionality, positioning their
combination as a promising synbiotic strategy.