Curcumin treatment enhances bioactive metabolite accumulation and reduces enzymatic browning in soybean sprouts during storage

Abstract

Curcumin is a natural polyphenol that is widely used in food and medicine. Here, we investigated the effects of curcumin on the antioxidant accumulation and enzymatic browning of soybean sprouts after storage at 4 °C for 2 weeks. Curcumin drastically reduced the water loss, browning index, and peroxide accumulation, increased the activities of superoxide dismutase, catalase, and peroxidase, decreased the activities of phenylalanine ammonia-lyase and polyphenol oxidase, elevated the contents of ascorbic acid, reduced glutathione, nonprotein thiol, phenolics and isoflavones, and enhanced the total antioxidant capacity of soybean sprouts during storage. These curcumin-induced changes were partly but dramatically attenuated by inhibition of NADPH oxidase (NOX). Curcumin induced NOX activity and H₂O₂ burst in soybean sprouts during the first 24 h after treatment. The curcumin-induced antioxidants and -inhibited enzymatic browning are closely associated with NOX-dependent H₂O₂ signaling. The findings provide a new method for improving soybean sprout quality during storage.

Keywords: Enzymatic browning; H2O2 signaling; Polyphenol; Postharvest vegetable.

Fig. 1

Curcumin reduces browning and lipid peroxidation. Curcumin regulates the water loss (A), browning index (B), lipid peroxidation (C), and H₂O₂ content (D) of soybean sprouts during storage at 4 °C. Bars represent standard deviation of the mean (n = 3); means associated with the same letter are not significantly different (p < 0.05). DPI, diphenyleneiodonium chloride.

Fig. 2

Curcumin enhances NADPH oxidase activity and H₂O₂ content. Curcumin regulates the NADPH oxidase activity (A) and H₂O₂ content (B) of stored soybean sprouts after treatment for 0, 6, 12, 18, and 24 h. Bars represent standard deviation of the mean (n = 3); means associated with the same letter are not significantly different (p < 0.05). DPI, diphenyleneiodonium chloride.

Fig. 3

Curcumin affects the enzyme activities. Curcumin regulates the activities of SOD (A), CAT (B), PAL (C), PPO (D), and POD (E) in soybean sprouts during storage at 4 °C. Bars represent standard deviation of the mean (n = 3); means associated with the same letter are not significantly different (p < 0.05). SOD, superoxide dismutase; CAT, catalase; PAL, phenylalanine ammonia-lyase; PPO, polyphenol oxidase; POD, peroxidase; DPI, diphenyleneiodonium chloride.

Fig. 4

Hypothetical model for how curcumin inhibits enzymatic browning. A hypothetical model for curcumin-induced inhibition of enzymatic browning in soybean sprouts during storage via activation of NOX-mediated H₂O₂ signaling. The sharp and blunt arrows represent positive and negative effects, respectively. Curcumin enhanced the antioxidant capacity, which inhibited the activity of PPO, and prevented contact between phenolics and PPO by maintaining the membrane integrity. For more details, see the text. AA, ascorbic acid; NOX, NADPH oxidase; PPO, polyphenol oxidase; DPI, diphenyleneiodonium chloride.