Structural and Functional Properties of Heat-processed Soybean Flour: Effect of Proteolytic Modification

Heat processing of soybeans alters its structural behavior, solubility, and in turn the functional properties. Heat-processed soy flour was prepared by autoclaving the defatted soy flour at 121 degrees C at 15 psi. The effect of enzymatic modification on the structural changes and functional properties of heat-processed soy flour was investigated. The combination of heat processing and enzymatic modification was carried out in two ways: (1) enzymatic modification followed by autoclaving and (2) autoclaving followed by enzymatic modification. Defatted soy flour (control), autoclaved soy flour, enzyme-modified flour, enzyme-modified and then autoclaved flour, autoclaved and then enzyme-modified flour were analyzed for physico-chemical and functional properties. Molecular weight profile of the protein was altered depending on the nature of treatments. Structural studies showed that enzymatic modification gave a porous type morphology to the particles. Enzymatic modification of autoclaved soy flour increased its surface hydrophobicity to 3136 +/- 400 units from 600 +/- 100 units of autoclaved soy flour. The results indicated that enzymatic modification of autoclaved soy flour increased its acid solubility (pH 4-4.5) from 17% to 56% over a control value of 24%. The foaming capacity of the enzyme-modified and then autoclaved soy flour was 80% while that of the autoclaved and then enzyme-modified flour was 42%. The soy flour that was autoclaved and then enzyme modified showed better emulsifying properties (174mL oil/g flour) than the flour that was enzyme-modified and then autoclaved. The modified soy flour based on its functional and physico-chemical properties should find application in many food systems.