Texturization of soybean (Glycine max L. Merrill) flour using a locally fabricated extruder

Fibrous appearance of extrudates was more prominent at temperature of 100-110 deg C, moisture content of 30-40% and low-oil content. Textural integrity index (TII) increased with increase in temperature and decreased with increase in moisture content. The highest TII of 0.75 was obtained from extrudate of partially defatted soyflour (10.5% fat) at 40% feed moisture content and extrusion temperature of 110 deg C. There was no definite trend obtained with regard to TII and oil content. Some of the extrudates from full-fat soyflour gave TII of 0.68 to 0.70. Protein solubility of the extrudate in water (nitrogen solubility index, NSI) or buffer solution decreased with increasing temperature and increased with increase in moisture content. NSI was reduced from 95.5% to 10.72% while solubility in buffer was reduced to 7.7%. Protein solubility showed that the solubility in buffer and buffer + 0.005 M dithiothrietol (DTT) is the same (7-15%) indicating that SS bond is not responsible for texturization on the surface of the denatured protein. Protein solubility was increased to 77% with the addition of 0.2 M sodium dodecyl sulfate (SDS). This indicates the presence of noncovalent or hydrophobic bonds on the surface of the extrudates. The combination of SDS and DTT in buffer increased the solubility to 99%. This means that both noncovalent and disulfide bonds play important roles in the texturization of soy protein. WAC [water absorption capacity] increased by 110% to 200% after extrusion. The disappearance and reduction in intensity of protein bands after extrusion was observed in polyacrylamide gel electrophoresis. Urease activity and trypsin inhibitor activity was reduced by thermoplastic extrusion. Both urease and trypsin inhibitor activity decreased with increase in temperature and increased with increase in moisture content. Lipoxygenase was completely inactivated at all conditions used. Soluble sugar increased slightly after extrusion. The reducing sugar increased with increase in temperature. This is accounted to the breakdown of sucrose and other oligosaccharides present in soybean. Extrusion has no effect on fatty acid composition of the exudates. The fatty acid composition of the samples remained the same before and after extrusion