Chemical composition and functional properties of three soy processing by-products (soy hull, okara and molasses)

Three soy processing by-products, soy hull, okara, and molasses, were analysed for their amino acids, fatty acids, dietary fibre, and other chemical compounds. Their digestibility and odour variance were also quantified. Okara had the greatest content of protein (306.1 g/kg) and amino acids (340.6 g/kg dry matter; DM), while soy hull had the highest amount of dietary fibre (546.7 g/kg) and extractable pectin (47.4 g galacturonic acid equivalents/kg DM), and molasses possessed the most abundant total phenolics, resulting in its highest radical scavenging activity. The high unsaturated fatty acids presented in soy by-products (accounting for 73.1-82.3% of total lipids) indicated their favourable physiological functions. In simulated digestion test, the by-products generally underwent fast digestion within the first 30 min in gastric digestion step, and then slowed down. However, okara was still digested rapidly in the stimulated intestinal digestion stage. Electronic nose was able to clearly discriminate the odour differences among the three soy by-products.