The effects of eugenol emulsion (EUG) on the browning of fresh-cut yam during storage and its inhibition mechanism were studied. The EUG treatment group had a significant anti-browning ability, and the 1.5% EUG treatment group had the best effect. During the whole storage period, the activities of peroxidase (POD) and phenylalanine ammonia-lyase (PAL) decreased significantly after 1.5% EUG treatment, especially on day 4, when the activity of POD and PAL was 3.2% and 23% of that of the control group, respectively. Molecular docking experiments showed that EUG inhibited PAL activity by binding to the active center of PAL, a key browning enzyme. A decrease in total phenol content was also observed. In addition, after EUG treatment, catalase (CAT) activity was significantly increased, preventing the accumulation of reactive oxygen species (ROS)-H 2 O 2 . EUG inhibited membrane lipid metabolism, 1.5% EUG delayed the emergence of lipoxygenase activity peak, and malondialdehyde (MDA) content decreased by 75.67% compared with the control on 4 d. In comparison with control, EUG increased the scavenging capacity of DPPH, ABTS, and iron-reducing antioxidant capacity (FRAP). The mechanism may be that EUG enhances antioxidant capacity, thereby reducing ROS-induced membrane lipid metabolism, therefore, lowering the synthesis and oxidation of phenolic compounds, and ultimately inhibiting browning.
Yellowing is a main discoloration in fresh-cut yam, which reduces consumer acceptance and, hence, the commodity value. Bisdemethoxycurcumin has been demonstrated to play important roles in fresh-cut yam yellowing. Considering the pharmacological properties and application in fruits and vegetables of diphenyliodonium iodide (DPI), the effects and mechanism of DPI treatment on bisdemethoxycurcumin accumulation in fresh-cut yam were analysed. The results showed that total bisdemethoxycurcumin in fresh-cut yam treated with DPI was markedly inhibited due to the significantly weakened phenylpropanoid pathway and bisdemethoxycurcumin biosynthesis. DPI was found to suppress the activities of major enzymes (phenylalanine ammonia lyase, PAL, cinnamate-4 hydroxylase, C4H; 4-coumarate coenzyme A ligase, 4CL), limit the levels of PAL, C4H and 4CL transcription and lower the contents of related metabolites in fresh-cut yam. Moreover, treatment with DPI inhibitor restrained the downstream transcription level of curcumin synthase (CURS), which had a significant impact on bisdemethoxycurcumin synthesis. Thus, our results confirmed that DPI was essential for inhibiting bisdemethoxycurcumin accumulation in fresh-cut yam through suppressed phenylpropanoid pathway and bisdemethoxycurcumin biosynthesis.
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