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Adapted from Hachmeisterand Fung, 1993 and Winarno and Reddy, 1986

2Whole raw soybeans (prior to soaking) 3Fresh (wet) weight basis

Adapted from Hachmeisterand Fung, 1993 and Winarno and Reddy, 1986

2Whole raw soybeans (prior to soaking) 3Fresh (wet) weight basis

Most of the free fatty acids are subsequently oxidized by R. oligosporus, resulting in a 10% decrease in the total dry matter in the finished tempeh. In fact, the relative inability R. oligosporus to metabolize the available soy carbohydrates (mainly stachyose, raffinose, and sucrose) means that fatty acids serve as the primary energy and carbon source.

In contrast, only about 10% of the released amino acids and peptides are oxidized by R. oligosporus. Of the remaining portion, about 25% are assimilated into biomass, and the rest is left in the tempeh.The soluble nitrogen concentration, therefore, increases four-fold, from about 0.5% to 2%. Despite the limited metabolism of proteins and amino acids, ammonia accumulates during the tempeh fermentation, such that the pH rises from 5.0 to above 7.0. This increase in pH during the fungal fermentation stage underscores the importance of acidification during bean soaking, since the latter step is responsible for inactivating potential pathogens that may have been present in the starting material. Once the low pH barrier no longer exists, neutrophilic pathogens could theoretically grow and cause problems.

Polysaccharide-hydrolyzing enzymes are also produced by R. oligosporus. These enzymes attack pectin, cellulose, and other fiber constituents, releasing various pentoses (xylose, arabinose) and hexoses (glucose, galactose). However, the activity of these enzymes during the tempeh fermentation is modest, and only minor amounts of free sugars are found in the final product.

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