Physico-chemical studies of extrusion texturization of plant proteins

Abstract

In order to understand the function of various additives in the development of texture in extruded texturized defatted soy flour, various divalent ions, sugars, proteins, and phytic acid were added to defatted soy flour in varying concentrations, and the products were evaluated by microstructural and rheological methods after extrusion. The phytate reaction proved to be pH dependent, with lesser effects on texture development at lower pH levels of the extrudate. The structural response of the extrudate to varying phytic acid concentrations was not linear, with maximum structural development at 3% concentration. The addition of selected divalent ions enhanced markedly the extrudate textural development. However, extrudate responses to these additives became complex at 6% concentrations and above. Anions were shown to play a greater role in texture development than cations. In general, sugars were disrupters of texture. They produced compacted products with very high densities and small diameters. Only at very low concentrations were they shown to enhance texture development. Effects produced with different concentrations of wheat gluten, soy, cottonseed, and peanut isolates made it evident that, although all of these proteins assisted in texture development, none had a directly linear effect on texture formation except cottonseed isolate. Micrographs of extrudate cell walls produced at maximum concentrations of the different proteins appeared dissimilar in nature, yet all cell walls followed similar patterns of stretching, elongation, continuity of protein matrix, and dispersion of carbohydrates.