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 °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.Copyright © 2006 Society of Chemical Industry