Scientific aspects of the fermented soybean food, tofuyo
2010
Yasuda, M., Ryukyu Univ., Nishihara, Okinawa (Japan). Faculty of Agriculture
Scientific aspects of tofuyo, low-salt fermented tofu, has yet to be fully clarified. The present study describes chemical characteristics of tofuyo and roles of fungus Monascus in food production. Fermentation of tofuyo is unique with respect to its soybean proteins, which undergo limited hydrolysis by proteinases in the presence of ethyl alcohol originating from awamori (distilled liquor). The main components forming the body of tofuyo consist of basic subunit of glycinin and other polypeptides (Mr. 55 kDa, 11-15 kDa). The soybean proteins were digested into peptides and amino acids during maturation. The amount of free glutamic acid and aspartic acid was greatly related to good taste (umami-taste) of the product. Some of the liberated peptides (IFL and WL) inhibited angiotensin I-converting enzyme activity that produces the vasopressor peptide. As WL was completely preserved after treatment with gastrointestinal proteases, it was expected to have an antihypertensive effect. Homogeneous preparation of proteinase from Monascus was characterized as an aspartic enzyme, a 'key enzyme' for ripening, chemical and physical properties, and formation of bioactive peptides of the product. Carboxypeptidases of this fungus were characterized as serine peptidases, which contribute to the release of amino acids from soybean proteins and their related peptides and to the removal of bitterness during hydrolysis of soybean proteins. We established a production method of a new type of tofu using an alkaline serine proteinase with high soybean-milk-coagulating activity isolated from Bacillus pumilus TYO-67. We prepared a new fermented foodstuff using soybean protein isolates. This method has the potential benefit for improving nutrition and adding physiologically functional properties to soybean foods.
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