| Abstract: | Starches from corn and sorghum masas were solubilized in water and their molecular characteristics were studied with high-performance, size-exclusion chromatography (HPSEC). Rheological properties of masa (smoothness, plasticity and cohesiveness) that are developed during lime-cooking, steeping and grinding of cereals were correlated to the starch solubility. Corn and sorghum were processed at different cooking times and grinding conditions; and the starch in masa was extracted with water at 85°C and 120°C for HPSEC analysis. Starches from corn and sorghum masas were affected in a similar way by the nixtamalization process; however, sorghum starch was more soluble than corn starch in flour and masa. Alkaline-cooking, steeping and stone-grinding did not depolymerize the cereal starch. All masas contained less than 10% soluble solids of which 30 to 50% was starch solubilized. Soluble solids increased with longer cooking time and finer grinding. About 50% of the insoluble starch, which remained in the particulate solids of masas was solubilized in water at 120°C. The remaining starch was indispersible because either the starch remained inside endosperm pieces or inside gelatinized and retrograded gels. Several granular and molecular forms of starch were present in masa as a result of partial gelatinization, i.e. uncooked, swollen, and annealed starch granules, and soluble and retrograded amylose. Retrogradationo f starch polymers occurred during steeping of cooked corn and during cooling of masa after grinding. Masa, a unique dough system, resulted from a network of starch polymers, uncooked and partially gelatinized starch granules supporting the rest of the kernel components into a continuous phase of water. |
