Identification of vegetable ingredients that enhance softening of kombu

Abstract

   The study aimed to reveal the ingredients in vegetables which enhanced softening of kombu when boiled with kombu and vegetables. The edible portion of 8 different types vegetables: spinach, garland chrysanthemum, daikon, edible burdock, eggplant, tomato, asparagus, cauliflower were boiled for 40 minutes with Kombu; the weight ratio for the deionized water : vegetable : kombu was 50 : 10 : 1, and after boiling, the swelling ratio and rupture stress were measured. Kombu was significantly lowered of rupture stress when boiled with spinach compared with the other vegetables. As a result of broth analysis, oxalic acid was only detected in the broth of kombu and spinach. In the next, kombu was boiled in the adjusted solutions, which were each organic acid contained in the vegetables: oxalic acid solution significantly lowered in rupture stress of kombu compared to the other organic acid solutions. The results indicated that it is the oxalic acid in spinach which softens the kombu when the two are boiled.