Microwave Heating for Solubilization of Polysaccharide and Polyphenol from Soybean Residue (Okara)

Okara, a soybean by-product of tofu production, was treated with microwave irradiation in water for solubilization of its components. The solubilization rate increased with increasing temperature and reached higher than 70% around 200°C with a heating time of 7 min. The main solubilized components were neutral carbohydrates consisting of arabinose and galactose, while the residues were mainly composed of cellulose. LV-SEM images confirmed solubilization of cell wall components. Production of new polyphenolic compounds that have antioxidant activity was observed above 180°C. The heating temperature and heating time were optimized for neutral carbohydrate solubilization using the response surface methodology. The optimized condition was heating at 196°C for 2 min, indicating that a short heating time is effective for solubilization of carbohydrates to prevent secondary decomposition.