Effect of the addition of calcium hydroxide on some characteristics of extruded products from blue maize (Zea mays L) using response surface methodology

The aim of this research was to study the effects of calcium hydroxide (0-0 .2%) and screw speed (100-180rpm) on the expansion index (EI), bulk density (BD), penetration force (PF) and specific mechanical energy (SME) values o f blue maize meal extrudates. Blue maize meal was extruded using a commerci al extruder (Brabender 20DN/8-235-00) with a compression screw ratio of 3:1 . A second-order, central composite experimental design was used. It was fo und that the El and SME values decreased and the BD and PF values increased when the calcium hydroxide concentration was Increased. The screw speed ha d a significant effect only on the SME and PF values. Quadratic model fitne ss was shown for all responses, with values of R-2 > 0.74, p of F (model) < 0.01 and variability coefficient < 13.3% (except for PF, 29.18%), and for a lmost all cases there was no lack of fit (p > 0.055). Calcium hydroxide con centration showed good correlation (p < 0.01) with EI (r = -0.81), PF (r = 0.60), SME (r = -0.76) and BD (r = 0.83). However, screw speed was marginal ly or not correlated (r < 0.36, p > 0. 14) with the responses. The results suggest that it is possible to produce appropriate extruded products from b lue maize fortified with calcium in an optimised calcium hydroxide concentr ation and screw speed range of 0.02-0.078% and 117-180rpm respectively. (C) 2001 Society of Chemical Industry.