Changing the Concentration of the Culture Solution before Harvesting Affected the Component Quality of Takana (Brassica juncea var. integrifolia)

Takana (Brassica juncea var. integrifolia), which is widely cultivated in warm regions of western Japan, is mainly pickled in salt. Takana, called Mamba in Kagawa Prefecture, is commonly used as an ingredient in local cuisine. Takana contains lye and has a strong bitter taste. Therefore, it is necessary to remove lye from Takana by boiling and soaking in water before cooking. Nitrate nitrogen, which is accumulated large amounts in leafy vegetables such as Takana (Yorifuji et al., 2005), is the main source of lye (Noda and Makuta, 2015). Nitrates are reduced to nitrites in the body and can cause methemoglobinemia in infants (Okabe, 1977). In addition, nitrites may combine with secondary amines to form suspected carcinogenic nitrosamines (Okabe, 1977). Boiling and soaking in water has been used to reduce harmful substances, such as nitrate nitrogen in Takana, but causes a reduction in useful components, such as ascorbic acid. Therefore, if Takana with low nitrate nitrogen content could be produced, useful components could be preserved because boiling and soaking would not be required. The nitrate nitrogen content of vegetables has been studied in many leafy vegetables. For example, studies using lettuce (Lactuca sativa L. var. youmaicai), Mizuna (Brassica rapa L. Japonica Group), Komatsuna (Brassica rapa var. perviridis), Cos lettuce (Lactuca sativa L. cv. Parris Island) and spinach (Spinacia oleracea L.) have found that nitrates accumulated in plants is affected by nitrogen application (Takebe et al., 1995; Shinohara et al., 2007; Kondo et al., 2008; Konstantopoulou et al., 2010; Fu et al., 2017). The nitrate content of hydroponic spinach and Mizuna was decreased by changing the culture solution before harvesting (Yoshida et al., 1998; Tsukagoshi et al., 1999; Kawaguchi et al., 2006; Kirimura et al., 2015). Based on these studies, we think it is possible to produce Takana with the low nitrate nitrogen content by controlling fertilizer components. In this study, the culture solution was changed before harvesting hydroponic Takana to establish a technique for reducing nitrate nitrogen content of Takana, and the effect on nitrate nitrogen content was investigated. The effects of the culture solution concentration on the ascorbic acid content was analyzed, and the growth conditions suitable for the cultivation of high-quality Takana were examined.