**2.1 Soybean paste**

Soybean paste was originated in China about 2,500 years ago. It is commonly known as Jiang in China, Miso in Japan, Doenjang in Korea, Tao-tjo in Indonesia and Thailand, and Tao-si in Philippines. There are series of soybean paste products in each country. Though they are made with soybean and cereals in the presence of salt, they have special tastes and flavors because of the different ratio of substrates, salt concentration, and the length of fermentation and aging (Fukushima, 1979). The salt concentration of fermented soybean paste is ranged from 4-11%, and the pH is about 5 (Shibasaki and Hesseltine, 1962). Soybean

Salt-Tolerant Acid Proteases: Purification, Identification,

different country ranges from 10-21% (Stute et al., 2002).

**3.4 Fermented whole soybean products** 

China (Wang et al., 2008).

**3.5 Soybean curd** 

**3.6 Enzymes** 

**3.2 Soybean paste** 

**3.3 Soy sauce** 

Enzyme Characteristics, and Applications for Soybean Paste and Sauce Industry 313

Cultures of *Aspergillus oryzae*, which known as a seed mold, are commonly used as starter for the production of soybean paste (Fukushima, 1979). Rice or barley is steamed and inoculated with *Aspergillus oryzae* to make koji. After completion of fermentation, the resulting koji is mixed with salt, cooked whole soybeans, pure cultured yeasts, lactic acid bacteria, and water, and then kept for an appropriate period for the second fermentation. The resulting aged mixture is mashed and packaged as miso. In general, miso is a paste of bright yellow to dark brown color. Whiter miso contains more rice than soybeans, whereas the darker miso contains 50 to 90% soybeans (Abe et al., 2006). The molds produce amylases and proteases which hydrolyze the cereal starch and the proteins in soybeans and cereals.

Cultures of *Aspergillus oryzae* are also used as starter for the production of soy sauce. The manufacturing of soy sauce is carried out as follows (Fukushima, 1979). Soybeans, or defatted soybean flakes, are moistened and cooked under pressure until they are sufficiently soft. The cooking was done in a batch type or a continuous cooker which allows a high pressure. On the other hand, the wheat is roasted by continuous roasting and then cracked into four to five pieces. The cooked soybean and wheat are mixed and then inoculated with a pure culture of *Aspergillus oryzae* to make koji. After two or three days, the well fermented koji is mixed with yeasts, lactic acid bacteria in the presence of more than 18% salt water which excludes undesirable microorganisms in the second period fermentation. The pH drops from an initial value of 6.5-7.0 down to 4.7-4.8. After fermentation, the product is filtered, pasteurized and packaged as soy sauce. The salt concentration of soy sauce from

Fermented whole soybean products are made of microorganisms with nindehulled soybean. *Bacillus natto* (Murooka and Yamashita, 2008) and *Bacillus subtilis* (Kim et al., 2011) are the bacteria used for Natto production in Japan and Chungkookjang in Korea, respectively. *Rhizopus oligosporus* is the principal fungus used for the Tempeh preparation in Indonesia. *Bacillus subtilis* and *Rhizopus microsporus* are used in different kinds of Dou-chi production in

*Actinomucor* spp., i.e. *A. elegans* and *A. taiwanensis*, and *Rhizopus* spp., i.e. *Mucor sufu* and *Mucor wutungkiao* are used as starters for high quality sufu making (Han et al., 2001). After preparation of tofu from soybean, one or more types of the above microorganisms are inoculated to ferment pehtze. The pehtze is transferred to salt-saturated solution to adsorb salt until the salt content of pehtze reaches about 16%, which takes 6–12 days. After maturation with different kinds of dressing mixture, different kinds of sufu are produced.

Manufacturing processing of fermented soybean product requires to uniform of the quality of the product. However, it is difficult to control the natural fermentation according to the traditional method using microorganisms as starters. Because high salt concentration is needed in fermentation of soybean products, salt-tolerant hydrolytic enzymes, especially

paste is consumed in large different ways in different countries. It is used as the base for sauces served with meat, seafood, poultry, or vegetable dishes in China, while it is used as the base for soups in Japan and Korea (Fukushima, 1979).
