There are four major fermented soy foods (soy paste, soy sauce, tempeh, and natto) and three minor fermented soy foods (sufu, soy nuggets, and soy yogurts). Table 1 lists English names, local names, and general description and uses of fermented soy foods.
Fermented soy foods vary greatly in terms of microorganisms involved, methods of preparation, length of fermentation, principles, and end uses. It takes only a few days to prepare tempeh and natto, but preparation of the remaining types of fermented soy foods generally requires several months to complete. Except for natto and soy yogurts, which result from bacteria fermentation, all others are fermented mainly through fungal fermentation. In terms of end uses, most fermented soy foods, including soy paste, soy sauce, soy nuggets, and sufu, are generally served as seasonings in cooking or making soups. They contribute more flavor than nutrition to the diet. They are characterized by high salt content added during the second stage of fermentation, as well as the presence of certain by-products (such as acids, alcohols) from desirable fermentation. Both salt and by-products inhibit or slow down spoilage of these products and allow them to have a relatively long shelf life. The remaining types, including tempeh, natto, and soy yogurts, contain no added salt and are consumed as a part of a main meal. Thus, they contribute protein and oil to the diet besides their characteristic flavor. Approximate chemical composition of selected Asian soy foods is listed in Table 2.
There are also some similarities among some of these fermented soy foods. For example, fermented soy paste, soy sauce, and soy nuggets share the same type of microorganisms, Aspergillus sp. In addition, most fermented soy products start with whole soybeans that have been soaked and cooked. Only soy yogurt and sufu derive from soymilk and tofu, respectively.
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