Transcriptome and physicochemical analysis revealed the potential anti-browning mechanism of pre-cut L-cysteine regulated by ethylene on fresh-cut apples

Abstract

Enzymatic browning is one of the main problems during storage of fresh-cut apples. Pre-cut treatment with L-cysteine has been shown to effectively inhibit browning on fresh-cut apples, but its mechanism is still unclear. This work investigated the browning-related differentially expressed genes (DEGs) after pre-cut treatment with L-cysteine, and analyzed the relationship between ethylene biosynthesis and L-cysteine through combining with aminoethoxyvinylglycine (AVG) treatment. The results indicated that lots of DEGs related to ethylene biosynthesis on fresh-cut apples were up-regulated, and the ethylene content, 1-aminocyclopropane-1-carboxilic acid (ACC) synthase and ACC oxidase activities were also improved after pre-cut L-cysteine. Further analysis found that AVG alleviated the effects of L-cysteine on the browning index, polyphenol oxidase (PPO) activity, peroxidase (POD) activity, catalase (CAT) activity and glutathione reductase (GR) activity of fresh-cut apples. Also, L-cysteine combined with AVG pretreatment reduced total phenol content and improved phenylalanine ammonia-lyase (PAL) activity compared with individual L-cysteine pretreatment. In addition, ethylene pretreatment also inhibited the browning and PPO activity, and increased POD activity, CAT activity and total phenol content on fresh-cut apples, which was better than that of L-cysteine combined with AVG pretreatment. This indirectly confirmed that pre-cut L-cysteine inhibited the browning of fresh-cut apples partly through regulating ethylene biosynthesis in vivo. The work proposes a novelty viewpoint that enhanced ethylene accumulation before cutting is helpful to inhibit the browning of fresh-cut apples.