Modification of the Soluble Protein Content of Heat-Processed Soybean Flour

Abstract

An important and frequently observed effect of food processing is the reduction of protein nutritive quality. Heat treatment of soybeans can reduce the activity of trypsin inhibitors and thereby improve protein digestibility. Overheating, however, may destroy or reduce the availability of certain heat sensitive amino acids and reduce the nutritional value of soy protein. The simplest criterion used for the characterization of proteins is their solubility in various media. The objective of this study was to evaluate the thermal effect on protein solubility of soybean flour (SBF). Heat-processed SBF was obtained in a forced air oven at 120�C, and by exposing to microwaves at 2450 MHz frequency. Protein solubility was determined according to the procedure of Araba and Dale, based on the solubility of soybean proteins in 0.036 M KOH. The experimental data show that, whatever the heating process used, the heating time is negatively correlated with the protein solubility. To maintain a good nutritional quality to heated soybean flour, microwave treatment has to be shortly applied compared to cooking one.