New Cheese-Like Food Production from Soy Milk — Utility of Soy Milk Curdling Yeast

Soybeans are a traditional food in eastern Asia, particularly in Japan and China. They were eaten in 100 BC in China. The beans can be processed into Tofu, soy milk, fermented seasonings, soy sauce or Miso paste, and Natto and green beans. Soybeans have rich nutrition, protein lipid, and other functional substances such as isoflavones. However, soybeans are difficult to process for use as food because of tissue and cell wall hardness. Therefore, soybeans are conducted to do some treatments, e.g., boiling, steaming, roasting, crushing/grinding, and some enzyme treating, to eat soy protein easily. Soy storage proteins mainly comprise two proteins as 7S globulin composed with β-conglycinin and 11S globulin containing glycinin composed of 5 subunits. βConglycinin, included in 7S globulin, is composed of three subunits. To modify the physical properties of soy protein, a new type of enzyme for curdling soybean milk enzyme was purified as an extract from yeast. Yeast producing curdling soybean milk enzyme, the SCY003 strain, was isolated from 1345 yeast strains. According to the morphology, physiology, and molecular and characteristics, SCY003 was identified as Saccharomyces bayanus. The soy milk curdling enzyme having proteolytic activity was approximately 45 kDa and monomer protein. The optimum pH for the protease activity was pH 7.5; the optimum temperature was 50°C. The enzyme cleaved the β-conglycinin as α–, α′-, and part of glycinin as A3 A4, A1b, and A2 in soy protein by endoproteolysis. Soybean protein became loosely curdled with the addition of other proteases from microorganisms or plants. Soybean milk curdled after cleaving endoproteolysis enzyme in SCY003 strain. © 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The breaking point of curd curdled by enzyme was 58.4% strain. Their breaking stress was 10,900 (N⋅m–2). The brittleness point is 81.2% and 10,200 (N⋅m–2), and the brittleness of this curd produced using the enzyme was 727 (N⋅m–2). Brittleness of the curd produced by the enzyme was less. Their breaking point was greater than that of the curd produced using the glucono-δ-lactone (GDL). Furthermore, the curd had sticky and chewy texture. The curd made by enzyme has resilience more than normal Tofu. It is considered that the curd produced by enzyme was not like Tofu rheologi‐ cally.