Five white corn hybrids were processed (nixtamalized) using 10 different processing conditions; tortillas were prepared to establish relationships between corn composition, physical characteristics, and nixtamalization process or product properties. Corn hybrids were characterized by proximate analysis and by measuring Stenvert hardness, Wisconsin breakage, percent floaters, TADD overs, thousand‐kernel weight, and test weight. Corn characteristics were correlated with process and product variables (effluent dry matter loss and pH; nixtamal moisture and color; masa moisture, color, and texture; and tortilla moisture, color, and rollability). Process and product variables such as corn solid loss, nixtamal moisture, masa texture, and tortilla color were influenced not only by processing parameters (cook temperature, cook time, and steep time) but also depended on corn characteristics. Significant regression equations were developed for nixtamalization dry matter loss (P < 0.05, r2 = 0.79), nixtamal moisture (P < 0.05, r2 = 0.78), masa gumminess (P < 0.05, r2 = 0.78), tortilla texture (P < 0.05, r2 = 0.77), tortilla moisture (P < 0.05, r2 = 0.80), tortilla calcium (P < 0.05, r2 = 0.93), and tortilla color a value (P < 0.05, r2 = 0.87).

Cereal Chem. 77(2):254-258Nixtamalization is the primary step in the production of products such as corn chips, tortilla chips, tacos, and corn tortillas. The process involves cooking and steeping of corn in lime and excess water to produce nixtamal. Commercial nixtamalization results in 5-14% corn solids loss in the liquid generated during cooking-steeping and washing. Loss of corn solids not only causes economic loss to corn processors but also creates costly waste and wastewater disposal problems. Empirical results show that, besides corn kernel characteristics, processing parameters are critical variables influencing corn solids loss and effluent pH during nixtamalization. This work was designed to systematically study the impact of processing parameters on corn dry matter loss and effluent pH generated during nixtamalization by using response surface methodology. Corn cooking temperature and lime concentration were more critical factors influencing corn solid loss than were cooking and steeping time. In the ranges studied, total dry matter loss increased only up to ≈8 hr of steeping and then leveled off. By optimizing the nixtamalization protocol, effluent dry matter loss can be minimized.

Instant masa flour finds extensive use in the food industry for making tortillas, taco shells, tamales, corn chips, and tortilla chips, and as an ingredient in extruded snacks. Due to lack of standard techniques for measuring masa functionality, processors and end‐users use masa flour particle‐size distribution and rheological characteristics in an attempt to predict its end use. In this study, a commercial masa flour sample was characterized by fractionating on the basis of particle size. Physicochemical and functional properties of masa flour fractions were investigated to establish structure‐composition and functionality relationships. It was observed that Rapid Visco Analyser (RVA) pasting profiles of flour fractions and textural properties of dough prepared on rehydration were related to particle size, yet, upon regrinding, RVA profiles did not change as markedly as expected. Differences in RVA measurements of the sized fractions could not be explained on the basis of hydration rate or total starch content. It was concluded that masa dough textural and RVA characteristics may be influenced by the status of starch polymer structures formed during nixtamalization.

Cereal Chem. 77(2):101-104The oil absorption characteristics of a multigrain extruded and fried snack product were studied as a function of extruder screw speed and cooking temperature using a central composite response surface methodology (RSM). The extruded product was produced using a corotating twin screw extruder, dehydrated to a uniform moisture content, and subsequently deep-fat-fried at 192 ± 1°C for 10-40 sec to complete expansion. Significant RSM models were developed for oil absorption and extrudate water absorption index (WAI). According to the lowest oil model, absorption (19.9%) was obtained with an extruder screw speed of 218.6 rpm and a cooking temperature of 117.8°C. WAI reached a maximum at a screw speed of 221.9 rpm and a cooking temperature of 109°C. Oil absorption characteristics and extrudate WAI were significantly correlated (r = -0.84, P = 0.0002). The data suggest that extrusion conditions can be optimized to influence the physicochemical structures in the extrudate matrix so that oil absorption can be minimized.Publication no. C-2000-0209-03R.

Nixtamalization involves cooking and steeping corn in a lime solution, washing the corn (nixtamal), and stone grinding nixtamal to form a corn dough or masa. Masa is used to produce nixtamalized products (corn tortillas, tortilla chips, corn chips, taco shells, etc.) by forming and baking or deepfat frying. The degree of corn kernel cook determines the quality and texture of masa. Response surface methodology (RSM) was used as an experimental design to study the impact of process variables (cook temperature, cook time, initial steep temperature, and steep time) on the degree of cook measured using a Rapid Visco Analyser (RVA) and differential scanning calorimetry (DSC). RSM data exhibited significant (P < 0.005), although not predictive, linear models for RVA peak viscosity (r2 = 0.63), setback (r2 = 0.61), final viscosity (r2 = 0.61), and peak time (r2 = 0.57), indicating a dependence of these parameters on nixtamalization conditions. Peak viscosity, setback, and final viscosity increased linearly with steep time. DSC enthalpy (r2 = 0.83) and peak temperature (r2 = 0.89) of freezedried masa also exhibited significant (P < 0.0001) linear regression models with processing variables. DSC enthalpy increased with an increase in steep time, suggesting that starch is annealed during steeping. This study demonstrated that fundamental starch properties were altered on extended steeping during nixtamalization.