TWIN-SCREW EXTRUSION-COOKING OF SMALL WHITE BEANS (PHASEOLUS-VULGARIS)

Dry small white beans (Phaseolus vulgaris) were ground and processed t hrough a twin-screw extruder using three screw configurations of incre asing energy intensity. Products were made over a moisture range of 15 0-250 g/kg, and barrel temperatures of 56-184-degrees-C. Results were examined by means of response surface methodology. Extrudate propertie s were significantly dependent (P < 0.10) on both the screw configurat ion and extrusion conditions used. In general, as the energy intensity of the configuration increased, expansion ratio, starting viscosity a nd hot viscosity increased, while bulk density, ending viscosity, and trypsin inhibitor activity decreased. All properties could be mathemat ically described as a function of the feed moisture content, the die t emperature, and the specific mechanical energy consumption (SME) in Wh /kg, as determined on an 'as is' basis. R2 and overall P values ranged from 0.708-0.999 and 0.001-0.40, respectively. Residual trypsin inhib itor activity in the extruded products was low (<15%), and values belo w 10% were easily obtained. Trace amounts of ungelatinized starch gran ules could be found in all samples.