Nutritional value and health benefits of fermented soybean products

Abstract

Soybean seeds are seeds of legume that have been historically an important source of oil and proteins. The consumption of soybeans is elevating rapidly for its high benefits as soy meals and its sub-products. Although, limited numbers of countries produce soybeans, however the respective oil, meals and products are available in almost all countries of the world and they are widely traded. Fermentation is the method used commonly to produce various soy products; different fermentation methods are applied for different products. Various microorganisms were involved in different types of fermented soy products; the predominantly used strains are B. subtillis and Aspergillus. It’s proven that fermentation can improve the physicochemical and sensory quality of the soy products. Soy consumption has been associated with many potential health benefits in reducing chronic diseases such as obesity, cardiovascular disease, insulin-resistance/type II diabetes, certain type of cancers, and immune disorders. Although soybean has been widely used as a functional food, the molecular mechanisms for its multiple functions remain unclear. The aim of this project is to determine whether fermentation will improve the quality of soybean products in terms of increasing digestibility, enhanced nutrition and increase the antioxidative activity, leading to enhanced health benefits. Commercial one non-fermented soybean product; Tofu, as well as two fungal fermented soybean products; Sufu and Douchi, in comparison with raw soybeans were tested. Glutamic acid was the most abundant amino acid with the percentages 20.3, 19.4, 22.1 and 20.7 of total amino acids contents of soybeans, Tofu, Sufu and Douchi, respectively. Fermentation reduced the Arginine content, where Sufu and Douchi had the lowest values (3.4 and 4.7%) as compared to 8.6% in soybeans and Tofu. The main component of the protein extracts of fermented soybean products; Sufu and Douchi, were peptides with a molecular weight below 10 kDa. SDS-PAGE patterns of both soybeans and Tofu were similar. All the samples exhibited antioxidative activity with different levels. It

5 was estimated that, samples with high antioxidative activity contained a large amount of small peptides. The antioxidative activity could ascribe to the peptides derived from soybean proteins during the fermentation process. Extracts of fermented soybean products exhibited selective cytotoxic activity towards Ehrlich Ascites Tumor (EAC) cells in a concentration- dependent manner.