Effects of calcium hydroxide and screw speed on physicochemical characteristics of extruded blue maize

The effects of calcium hydroxide and screw speed on expansion, pasting, crystallinity, torque, water absorption, and solubility indices upon extruded blue maize meal products were studied, using a central composite experimental design. All the characteristics measured presented a significant quadratic regression model, indicating relationship between the responses and extrusion conditions. It was found that the expansion, crystallinity, torque, water absorption, and solubility indices decreased and the Rapid Viscosity Analyzer's (RVA) pasting characteristics increased with the increase of calcium hydroxide concentrations. The Pearson correlation indicated that the responses presented strong correlation (r > 0.7, p < 0.01) between them. Extruded products with physical appearance and expansion similar to the control were found at concentrations lower than 0.1% of calcium hydroxide.