Nixtamalized Flour From Quality Protein Maize (Zea mays L). Optimization of Alkaline Processing

Quality of maize proteins is poor, they are deficient in the essential amino acids lysine and tryptophan. Recently, in México were successfully developed nutritionally improved 26 new hybrids and cultivars called quality protein maize (QPM) which contain greater amounts of lysine and tryptophan. Alkaline cooking of maize with lime (nixtamalization) is the first step for producing several maize products (masa, tortillas, flours, snacks). Processors adjust nixtamalization variables based on experience. The objective of this work was to determine the best combination of nixtamalization process variables for producing nixtamalized maize flour (NMF) from QPM V-537 variety. Nixtamalization conditions were selected from factorial combinations of process variables: nixtamalization time (NT, 20–85 min), lime concentration (LC, 3.3–6.7 g Ca(OH)₂/l, in distilled water), and steep time (ST, 8–16 hours). Nixtamalization temperature and ratio of grain to cooking medium were 85 °C and 1:3 (w/v), respectively. At the end of each cooking treatment the steeping started for the required time. Steeping was finished by draining the cooking liquor (nejayote). Nixtamal (alkaline-cooked maize kernels) was washed with running tap water. Wet nixtamal was dried (24 hours, 55 °C) and milled to pass through 80-US mesh screen to obtain NMF. Response surface methodology (RSM) was applied as optimization technique, over four response variables: {In vitro} protein digestibility (PD), total color difference ( E), water absorption index (WAI), and pH. Predictive models for response variables were developed as a function of process variables. Conventional graphical method was applied to obtain maximum PD, WAI and minimum E, pH. Contour plots of each of the response variables were utilized applying superposition surface methodology, to obtain three contour plots for observation and selection of best combination of NT (31 min), LC (5.4 g Ca(OH)₂/l), and ST (8.1 hours) for producing optimized NMF from QPM.