Studies on the Firming Mechanism of Japanese Radish Root by Pre-heating Treatment

Abstract

The Japanese radish roots subjected to pre-heating treatment prior to boiling process in water were harder than the corresponding untreated control. A maximal hardening was obtained at 55°C for about 2hr, and this temperature was identical with the optimum temperature of pectinesterase (PE)contained in Japanese radish. The degree of esterification of the pectic substances was found to decrease greatly during this pre-heating treatment. Of the total pectic substances, the water soluble fraction decreased while the hot water soluble and hydrochloric acid soluble fractions increased in hardned tissues, compared with the untreated ones. A large amount of potassium ion leaked out into the soaking water from the tissues during pre-heating treatment at more than 50°C, on the other hand, amounts of leaked calcium and magnesium ions was relatively small. It was suggested that pre-heating treatment caused potassium ion migration prior to activation of the PE which was inactive in an intact tissue, and the activated PE promoted demethylation of the pectic substances in the tissue to cause hardening by combination of the resulted free carboxyl groups in the pectic substances and divalent cations in the tissue.