Accurate pH decrease induced inactivation of myrosinase and polyphenol oxidase in salted radish for color improvement

Abstract

Yellowing even browning of radish commonly occurred during the traditional pickling. This research aimed to determine the reason of yellowing of pickled radish, and propose the method for yellowing inhibition. The activity of endogenous enzymes in radish were analyzed, and the relationship between the activity and the browning was investigated. Myrosinase and polyphenol oxidase (PPO) were found as main potential enzymes resulting in browning of radish. During traditional salting processing, the myrosinase activity decreased, particularly at a high speed in the first 14 days, while the PPO activity did not decrease observably. The a* and b* values of salted radish were significantly correlated with myrosinase and PPO activity. Acid treatment was observed to be effective for browning inhibition of radish during soaking and storage, and the low pH conditions contributed to the preservation of original green color of radish. Stronger acidification during the first 3 d played a much more important role in browning inhibition than following weaker acidification treatment for 27 d. Low pH showed an inhibition effect on PPO activity, but myrosinase reactivity was more sensitive to pH changes than PPO. The myrosinase in the radish treated in the pickling solution at pH 2 was completely inactivated during the first 3 days. Further investigation of pH effect on improvement of salted radish color concluded that pH 2.4 was the optimal pH for the inactivation of myrosinase and PPO. Accordingly, short-term accurate acidification coupled with traditional salting treatment was originally proposed for effective browning inhibition of pickled radish.