It has been said that the texture of foodstuffs becomes harder during the process of cooking when the soy-sauce (shoyu) was used. Experiments were carried out to investigate the changes in the texture of various foodstuffs when they were cooked with shoyu, and also to find out what the chemical components of shoyu will cause the texture of the cooked foodstuffs harder.
The following results were obtained :
1. It was clearly shown by curdmeter measurements as well as by sensory tests that the foodstuffs such as soy beans, radishes (daikon) and potatoes cooked with shoyu became harder than those which are cooked with the sodium chloride solution whose concentration is the same as shoyu.
2. When soy beans were cooked with the several kinds of solutions which contain the major components of shoyu, the solutions of carboxylic acids and amino acids have made the soy beans harder than the distilled water or sodium chloride solution was used.