Effect of extrusion on nutritional quality of maize and Lima bean flour blends

Maize flour (Zea mays) (M), Lima bean flour (Phaseolus lunatus) (B) and blends of these in proportions of 75M/25B, 50M/50B and 25M/75B (w/w) were extruded and their nutritional quality evaluated. Extrusion was done with a single screw extruder at 160 degrees C, 100 rpm and 15.5% moisture. In vitro protein digestibility (87%) was higher in the extruded products. Available lysine and resistant starch were highest in 50M/50B raw flour (59.5 g kg(-1) protein, 67.9 g kg(-1), respectively) but decreased after extrusion (45.5 g kg(-1) protein, 16.6 g kg(-1), respectively). The same treatment had the lowest available starch (561.6 g kg(-1) flour, 507.9 g kg(-1) extrudate). Total dietary fiber in the 50M/50B raw flour blend was 144 g kg(-1) versus 176 g kg(-1) in its extrudate. This was most noticeable for soluble dietary fiber, which increased from 10.6 g kg(-1) to 79.4 g kg(-1) after processing. Extrusion of blends is feasible up to a 50% bean inclusion level, which improves the nutritional value of the expanded product. (c) 2006 Society of Chemical Industry.