Reactive extrusion and enzymes were utilized to hydrolyze non-starch polysaccharides in pinto bean flour and increase dispersion of starch, protein, and dietary fiber. Discussion includes conditions for improvements in physical functionality.
Pinto bean, a variety of the common bean (Phaseolus vulgaris L), is an important crop in North America with significant export value. Legumes such as pinto beans are an excellent source of nutritious protein, starch, and dietary fiber. Industrial implementation of beans as a source of starch is limited by its restricted swelling power, poor granule dispersibility, high gelatinization temperature, higher syneresis, and resistance to enzymatic hydrolysis when compared to traditional commodity sources. Beans also contain a significant fraction of structural pectins and hemicelluloses. As a means to increase physical function of starch and dietary fiber components of bean flour, a combination of enzymatic hydrolysis and high-moisture extrusion was used to breakdown the fibrous components. Viscometric analyses demonstrated that enzymes with hydrolase activity toward pectin and hemicellulose were effective in changing the consistency of heat-treated bean flours. Reactive extrusion at different bean flour contents was then applied as an integrated single step process akin to a bioreactor, wherein the bean flour, moisture, and enzyme were simultaneously extruded at temperatures permitting enzymatic activity. Hydrolysis and associated changes in physical functionality of the flours were assessed by rheometry and soluble fiber contents. Results from the study address the effects of reaction conditions and contents on the physical and chemical structure of bean flour suspensions, as well as provide indications for increased accessibility of starch and other components for further isolation or reaction. Such findings contribute to the capability of enzyme-assisted reactive extrusion processes for direct utilization of relatively complex flours and meals in lieu of isolated fractions.
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