Enzymatic Extractability of Soybean Meal Proteins and Carbohydrates: Heat and Humidity Effects

To study the incomplete enzymatic extractability of proteins and carbohydrates of thermally treated soybean meals, one unheated and three heat-treated soybean meals were produced. To obtain truly enzyme-resistant material, the meals were extracted by a repeated hydrolysis procedure using excessive concentrations of different combinations of commercial protease and carbohydrase preparations. The water extractability of protein from the different meals varied considerably (13−67%). For all soybean meals, enzymatic treatment extracted most of the original protein (89−94%). Carbohydrase preparations did not improve protein extraction. High-humidity heat treatment led to a more effective enzymatic extraction, which seemed to correlate with the extent of protein denaturation. Results with purified proteins indicated that the soybean meal matrix affects the enzymatic extraction of protein from the meals. Interactions between protein and other components (e.g., cellulose) may explain the incomplete enzymatic extractability of protein from the meals. Keywords: Soybean meal; heat treatment; hydrolysis; extraction; enzymatic residue; protease; carbohydrase; composition; protein; carbohydrate; amino acid