Deterioration Mechanism of Glucosinolate-Myrosinase System in Radish Roots during Cold Storage after Harvest

Abstract

The major isothiocyanates (ITCs) as a health benefit compounds in radish roots are raphasatin (RH) and sulforaphene (SFE). They are converted from precursor glucosinolates (GSLs), glucoraphasatin (GRH) and glucoraphenin (GRE), respectively, by activation of myrosinase. The process to form ITCs is called glucosinolate­myrosinase (G­M) system. In this study, we investigated the G­M system in roots of six radish varieties to understand the changes of G­M system during storage after harvest. Six varieties of radish roots were stored for 8 weeks at 0~1.5oC after modified atmosphere packaging. Five components consisting of G­M system, namely, ITCs concentration, GSLs concentration, myrosinase activity, ascorbic acid concentration, and myrosinase-related gene expression were measured respectively. The concentration of GRH and GRE, major GSLs of radish root, slightly decreased or maintained during entire storage days. However, the concentration of ITCs, especially SFE, and myrosinase activity were remarkably decreased until 8 weeks. Pearson correlation analysis using change rates of ITCs concentration, GSLs concentration, and myrosinase activity showed that a decrease of SFE concentration has a positive relationship (r = 0.684, P = 0.0017) to decrease of myrosinase activity during storage. Also, myrosinase activity related factors such as ascorbic acid concentration and myrosinase­binding protein gene expression were decreased during storage. Thus, a decrease of ITCs concentration that is the result of deterioration of G­M system might be caused by a decrease of myrosinase activity and myrosinase related factors. Our findings will provide an advanced view in order to maintain the quality of radish roots during storage, focusing on ITCs concentration, myrosinase activity, and myrosinase related factors but not GSLs concentration.