Objective Fresh-cut Chinese water chestnut (CWC) is prone to yellowing during storage, seriously affecting its appearance quality and commercial value. The study aims to find an effective method for inhibiting the yellowing of freshcut CWC and delaying quality deterioration during storage.

Method Fresh-cut CWC were soaked in rice bran extracts to study the inhibitory effects of rice bran extracts on yellowing by measuring the color, total flavonoids content, enzyme activity, and expression changes of structural genes and transcription factors related to flavonoid metabolism.

Result The rice bran extracts treatment significantly inhibited the increase of b* value (20.62 at 6 d of storage, significantly lower than the control) and the decrease of L* value (maintaining at 70 or above at 6 d of storage) of fresh-cut CWC during storage. Correspondingly, the rice bran extracts treatment significantly inhibited the increase in total flavonoids content, while the flavonoid content in control group increased to 0.377 mg/g at 6 days of storage, which was 2.96 times that of 0 d. In the control group, the polyphenol oxidase (PPO) activity decreased first and then increased in the later stage of storage, while the PPO activity in the rice bran extracts treatment group was significantly lower than that in the control group from 2 to 6 days of storage. The activity of PAL (phenylalanine ammonia lyase) in the control group rapidly increased throughout the entire storage process, and finally reaching 71.03 U/g at 6 d, which was three times that of 0 d. However, the rice bran extracts treatment significantly inhibited the increase of PAL activity. The quantitative real-time PCR (qRT-PCR) analysis showed that rice bran extracts treatment effectively inhibited the expression of key structural genes in flavonoid synthesis pathway, including CwPAL, CwC4H, CwCHI and CwCHS. The expression of CwMYB12 and CwMYC2 transcription factors related to flavonoid synthesis were both significantly suppressed by rice bran extracts treatment.

Conclusion Rice bran extracts can effectively delay the yellowing of fresh-cut water chestnut during storage, and has a significant inhibitory effect on the accumulation of flavonoids and flavonoid metabolism. These results provide a basis for further elucidating the molecular mechanism of CWC yellowing, and provide references for the preservation and color protection treatment of fresh-cut CWC.