Untargeted metabolomics reveals the mechanism of ultrasound combined with L-cysteine treatment inhibiting the browning of fresh-cut potatoes

Abstract

Freshly cut potatoes tend to brown during processing and preservation, which is an important issue worldwide. Ultrasound (US) combined with L-cysteine (L-Cys) treatment (US-L-Cys) has been reported to inhibit the browning of fresh-cut potatoes in our laboratory. However, the underlying mechanism remains to be elucidated. Untargeted metabolomics, a popular high-throughput technique, has been used to investigate the biochemical changes that are closely associated with the browning of fresh-cut fruits and vegetables. The present study investigated the effect of US-L-Cys treatment on the browning index (BI), related enzyme activities, total phenolic content, antioxidant capacity, malondialdehyde (MDA) content, and relative electrical conductivity of fresh-cut potatoes during 6-d storage. Metabolomics was used to compare the metabolites of US-L-Cys-treated and control samples on days 0 and 6. The results showed that US-L-Cys treatment reduced BI; decreased polyphenol oxidase, peroxidase, and phenylalanine ammonia-lyase activities; maintained high total phenolic content; increased antioxidant capacity; and decreased MDA content and relative electrical conductivity in fresh-cut potatoes during storage. Metabolomic analysis revealed that tyrosine and amino acid metabolisms were enriched. Higher levels of alanine and lower levels of dopamine were observed in US-L-Cys-treated samples compared with control samples. Therefore, depressed tyrosine and activated alanine metabolisms may be involved in the mechanism through which US-L-Cys inhibits the enzymatic browning of fresh-cut potatoes during storage.