Effect of extrusion cooking and sodium bicarbonate addition on the carbohydrate composition of black bean flours

Extrusion cooking and chemical leavening agents such as sodium bicarbonate (NaHCO3), may induce changes in carbohydrate fractions of extruded black bean (Phaseolus vulgaris L.) flours. Bean flours at 20% moisture, with NaHCO3 added at levels from 0.0 to 2.0%, were extruded at a screw speed of 200 rpm. The temperature profile ranged from 23 to 160C. Extruded bean flours with 0.1 to 0.4% added NaHCO3 were selected for sugar analyses based on color and flavor acceptability. The major sugars determined in the bean samples were galactose (0.10%), sucrose (2.08%), and stachyose (2.00%). Extruded samples had an increase in total sugars. Also, an increase in soluble fiber and a decrease of insoluble fiber fractions were observed. Sucrose was the only free sugar which concentration decreased consistently as a result of extrusion processing. Extrusion conditions and the selected levels of NaHCO3 used in this study did not significantly change the oligosaccharide content of the black bean flours.