Nitrate and Nitrite Contents in Japanese Radish and the Changes during Growing, Storage and Pickling Process

Studies on Nitrate and Nitrite in Horticultural Products (Part 7)

Abstract

Nitrate and nitrite contents and the activity of nitrate reductase of Japanese radish were analyzed during growing, storage and pickling with salt or salt-bran.
(1) The varieties of radish used in this experiments were Minowase-spring type (sowing, April; harvesting, end of June), Minowase No 2-summer type (sowing, August; harvesting, end of October), and Miyasige (sowing, September; harvesting, end of November).
2) Nitrate concentration in a root was higher toward the root tip and there were no significant difference in nitrate contents among cortex, vascular bundle and parenchyma at the middle part of the root.
3) Nitrate concentrations of the petioles, roots, and leaf blade were 1400-1600ppm, 700ppm, and 200-350ppm 40 days after sowing, respectively. During the growing stage from the above period to the harvesting date, nitrate contents of these parts decreased by about one-tenth of the initial ones. In Miyasige variety for which the times of fertilizing was increased, the decreasing rate for the period was about a half.
4) Nitrate reductase activity in Minowase-spring type was higher in leaf blade and lower according to the decreasing order of petioles and roots. During the growing stage, the activity increased in leaf blade, but were constant other two parts.
5) These three varieties of the radish roots were stored at 1 and 20°C. Changes of nitrate contents during the storage were not noted in both Minowase varieties, but in Miyasige, .itrate contents decreased slightly. Nitrate reductase activity were maintained at the low level during storage.
6) Changes of the amount of nitrate were observed through the process of pickling with saltbran. After 26 days, the amounts became to be the equal level of nitrate in the roots and saltbran. Maximum content of nitrite was only 0.4ppm in the process.
7) In the process of pickling with salt only, the changes of nitrate contents in the roots and in brine both at 6 and 20°C were similar to those of pickling with salt-bran. Nitrite contents had maximum, 3 days after the start of pickling at 20°C (30ppm in the root and 230ppm in the brine), but the formation of nitrite at 6°C was suppressed markedly.