Dry matter distribution in commercial alkaline-cooking processes for production of corn tortillas and snack foods

Abstract

Five commercial processes for alkaline-cooking of corn were studied in two plants which produce corn tortillas, tortilla chips and corn chips. Corn is cooked and steeped in water containing lime to hydrate and soften the kernel and remove the hull prior to stone-grinding to produce a dough called masa. The processing conditions studied were typical of most commercial alkaline-cooking operations. The objective of this comparative study was to determine how corn dry matter is distributed in the processed corn and wastewater during cooking, steeping, washing and grinding operations. A mass balance was done on the corn-water-lime system for each process to estimate the total dry matter lost during cooking and steeping. Masa was fractionated to isolate the particulate, cell fragment and dissolved solids components, which were analyzed separately. Total dry matter in wastewater and masa fractions was partitioned into starch, non-starch polysaccharides (NSP), protein, lipid and calcium. Corn dry matter losses were 8.5-12.5% for the four processes using overnight steeping, and 4.4% for a short-steep process. Corn pericarp was the major dry matter component in wastewater from commercial alkaline cooking. Wastewater suspended solids are easily recoverable and have potential value as a food ingredient. Soft corn varieties, severe cooking conditions, physical stresses and extended steeping were found to promote losses of starch, protein and lipid from corn during processing. Masa dry matter was shown to consist of particles larger than 63 μm (26-53%), free starch granules/cell fragments (41-65%) and dissolved solids/free lipid (5-9%). Masa particle size distribution was influenced more by grinding conditions than any other factor. Extensive starch gelatinization was found only in masa from corn given the most severe heat treatment. Free, partially emulsified lipid constituted 25-50% of total masa lipid. The free starch, free lipid and dissolved solids fractions may have active roles in developing the characteristic textures and flavors of tortillas and fried masa products.