Abstract
The internal blue discoloration of edible daikon roots often occurs on day 3 after harvest during storage at 20°C and is a serious problem. This study reports a rapid and simple method for predicting discoloration at harvest and proposes two methods for suppressing the discoloration of roots that are at discoloration risk. The soaking of freshly harvested roots in aqueous hydrogen peroxide resulted in immediate blue discoloration. The correlation between discoloration after storage at 20°C and discoloration after soaking in hydrogen peroxide was positive. Discoloration using hydrogen peroxide at harvest is a useful way of predicting discoloration risk. The storage of roots at 10°C in air or at 20°C in an atmosphere containing 1% (v/v) molecular oxygen resulted in no discoloration for at least 8 days. These storage conditions can guarantee no discoloration for the distribution after harvest.
Highlights
Daikon, the Japanese radish (Raphanus sativus L.), is an important, abundantly produced agricultural crop in Japan and is consumed as an edible white root vegetable (Figure 1 a,b)
Regarding the internal blue discoloration, in 2016 we showed that the only precursor for the formation of blue-colored compounds is 4-hydroxyglucobrassicin (Figure 2); blue components are formed by oxidation of the precursor molecule with reactive oxygen species produced from hydrogen peroxide in the presence of peroxidase (Teranishi & Nagata, 2016)
The Hukuhomare daikon cultivar has been known to suffer from internal blue discoloration in Japan
Summary
The Japanese radish (Raphanus sativus L.), is an important, abundantly produced agricultural crop in Japan and is consumed as an edible white root vegetable (Figure 1 a,b). Over the past decade in Japan, the appearance of an internal blue color has been observed in white daikon roots during distribution following harvest (Figure 1 c,d) (Ikeshita, Ishibata, & Kanamori, 2010). This physiological phenomenon does not occur at the time of harvest, as shown, and is only observed by consumers during preparation for cooking, leading to complaints to shopkeepers and farmers. The internal blue discoloration has not been reported to be harmful, the commodity value of affected daikon is reduced because of the strange blue color in the white roots This is a serious issue for both shopkeepers and farmers
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