Identification of novel starch and protein structures related to corn masa texture

Production of corn tortillas and tortilla chips first involves alkaline cooking of the kernels, followed by steeping and rinsing to yield smooth kernels known as nixtamal. Stone-milling the nixtamal generates the dough-like material known as mass, which is then sheeted and cut into the characteristic tortilla shapes. Masa should be adequately cohesive to resist breakage during rolling and sheeting, but not excessively adhesive so as to become sticky. The objective of this study was to identify specific chemical components within masa that are responsible for its cohesive/adhesive texture. Lime-concentration dependent complexation of proteins from heated lime:corn flour suspensions were observed using SDS-PAGE at concentrations above the saturation point of lime in solution. Another divalent ion-containing alkali, strontium hydroxide, produced a similar effect, while the effect of a monovalent ion-containing alkali was not as pronounced. Similar protein complexes were not readily apparent in masa. Gelatinized starch in nixtamal, estimated by β-amylase/pullulanase digestion, increased due to lime cooking from 11% to 16%. Intermediate pressure high-performance liquid chromatography (HPSEC) analysis of the water-soluble starch component from mass indicated that it increased in amount and molecular weight as cook time increased. This soluble fraction was similar to amylopectin with regard to λmax and isoamylase debranched profile, though of lower MW. It was termed “intermediate MW amylopectin-like component.” The amount of this component was highly correlated with masa adhesiveness (r = 0.890, P \u3c 0.01) and with cook time (r = 0.957, P \u3c 0.01). Amount of the intermediate MW amylopectin-like component was directly related to gap width of the stones in the masa mill and was concluded to be caused by amylopectin fragmentation due to shear force. Rapid detection of the intermediate MW amylopectin-like component can be achieved by using an iodine complexation assay. The results of this study strongly imply that the intermediate MW amylopectin-like component is the major determinant of masa texture and that its measurement can be used as a process control parameter