Understanding starch structure−function relationships is vital to the continued development for new uses for starch. Fractionated corn amylose and amylopectin, with known molecular weights, chain lengths, and branching and crystalline ratios, were studied for pasting, gel textural, and retrogradation properties by rapid viscoanalysis, textural profile analysis, and differential scanning calorimetry. Amylose fractions with weight-average molecular weights (M w) of 2.47−1.36E+05 had chain number-average degrees of polymerization (DPn) of 500−1000, 0−1 branch points per 1000 glucose units, higher setbacks, and high final viscosities and resulted in firmer gels than their lower M w counterparts. Cohesiveness was inversely proportional to crystallinity, while stringiness increased with increasing DPn. Amylopectin fractions of low M w (7.89−7.08E+07) with high branching ratios (>1.5), short branch chains (weight-average degree of polymerization, 15−18), and crystallinity >28% had high peak temperatures and low peak viscosity and shear thinned less. When cooled, these amylopectins formed weak gels, but during storage, the gels firmed and retrograded more than did their high M w counterparts. Keywords: Corn; amylose; amylopectin; pasting; textural profile analysis; differential scanning calorimetry; DSC; molecular weight; retrogradation; crystallinity

Characterization of starch molecular structure is vital to comprehending starch structure−function relationships. Four corn starches were fractionated by aqueous leaching into six amylose and five amylopectin fractions. Molecular weight (MW), branching, and chain lengths were determined by size exclusion chromatography and laser light scattering (SEC/LLS); percent crystallinity was determined by X-ray analysis. Amylose fractions had different weight-average molecular weights (M w = 1.03−4.89E+05) and branching ratios (0.3−1.0), and branching was seemingly inversely correlated with M w. Amylose fractions had similar polydispersities (1.3−1.9) and branch points per chain of 1000 glucose units (0.6−3.0). Degree of polymerization (DP) increased (324−1014) proportionally to M w. For amylopectin, some fractions had different M w values (7.08−9.88E+07) but statistically similar polydispersities (1.1−1.2) and branching ratios (1.5−4.3). The highest M w amylopectin fraction had longer branched chains (long, intermediate, short) than those of its lower M w counterparts. DP for short branched chains was correlated with M w. High to low M w amylopectin fractions with branching values >1.5, and short branched chains (DP = 15−18), showed high crystalline ratios (>28%). Similar MW and branching trends were observed in a previous study using SEC/refractive index and wet chemistry, respectively. These studies suggest that MW characterization possesses the potential for predicting some molecular structures in starch. Keywords: Starch; corn; amylose; amylopectin; molecular weight; branching; size exclusion chromatography; laser light scattering

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).

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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.