Effect of Lactobacillus acidophilus fermentation on bioaccessibility: The relationship between biotransformation and antioxidant activity of apple polyphenols based on metabolomics

Abstract

Apple (Malus domestica) polyphenols are strong antioxidants. However, the functional properties of apple polyphenols are limited due to their considerable low digestibility. Therefore, in this study, the effects of fermentation of apple pulp by Lactobacillus acidophilus on its total polyphenol content and antioxidant activity were assessed using metabolomics. The results showed that the total polyphenol content and antioxidant activity of apple pulp fermented with L. acidophilus zrx02 were significantly higher than those in the unfermented apple pulp. Six different significantly changed metabolites, including caffeic acid, hypericin, p-coumaric acid, p-hydroxybenzoic acid, ferulic acid, and eugenic acid, were selected using ultra-performance liquid chromatography-tandem mass spectrometry and a metabolomics analysis. A cluster analysis revealed that one group contained caffeic acid, while the other one contained ferulic acid, p-hydroxybenzoic acid, p-coumaric acid, hypericin, and syringic acid. Ten metabolic pathways with significant differences were screened using the hypergeometric method. Overall, the results suggest that after fermentation by L. acidophilus zrx02, apple polyphenols can be biotransformed into small molecules that are easily digested and absorbed, and they have improved antioxidant activity. It is a raw material source of antioxidant-rich active substances that merits full utilization.