Factors Affecting the Alkaline Cooking Performance of Selected Cornand Sorghum Hybrids

Cereal Chern. 87(6):524-531 Dent com (Zea mays L.) and sorghum (Sorghum hieolor L. Moench) sample sets representative of commonly grown hybrids and diverse physical attributes were analyzed for alkaline cooking performance. The influence of kernel characteristics including hardness, density, starch properties (thermal. pasting, and crystallinity). starch content. protein content. and prolamin content on alkaline cooking performance was also determined. Com nix tarnal moisture content was lower for hard, dense kernels with high protein contents; sorghum nix tarnal moisture content was lower for kernels with low moisture contents and low starch relative A major food use of corn (Zea Mays L.) and sorghum (Sorghum bicolor L. Moench) grain (kernel) is commercial production of tortillas, snack chips, and related foods through the alkaline cooking process known as nixtamalization (Serna-Saldivar et al 1988; Suhendro et al 1998; Taylor et al 2006). During nixtamalization, grain is cooked in a lime solution, allowed to steep for 12-16 hr. washed to remove loose pericarp, and stone-ground to produce masa (corn or sorghum dough) (Sahai et al 1999). Masa is then formed and cooked into desired end products. Nixtamalization efficiencies are of primary concern to processors and depend on three factors: 1) optimizing degree of cook; 2) optimizing pericarp removal; and 3) minimizing dry matter loss (DML) (Shandera et al 1997). During nixtamalization, thermal transfer due to hydration results in partial gelatinization of starch, limited granule swelling, and disruption of starch crystalline structure (Mondragon et aI2004). Degree of cook is determined by the rate at which kernels absorb moisture and it affects masa texture and final product quality (Sahai et al 1999). Slower moisture absorption, which is associated with harder kernels, assures product consistency (Shandera et al 1997). Pericarp removal is the primary purpose of the washing step. Pericarp in masa foods can have an adverse affect on texture, color. and processing properties (Serna-Saldivar et al 1991). However, complete removal of pericarp is not always desirable due to decreased product yield. Grain solids loss during cooking. steeping, and washing increases waste water disposal costs and decreases end product yield (Sahai et al 2000). While these factors are primarily influenced by processing 1 Department of Food Science and Technology. University of Nehraska-Lincoln. Lincoln. NE 68583-0919. 2 Agricultural Research DivisionINE Agricultural Experiment Station. University of Nebraska-Lincoln, Lincoln, NE 68583-0704. 3 University of Nebraska-Lincoln, The Food Processing Center, 222 Food Industry Complex. Lincoln. NE 68583-0930. 4Corresponding author. Phone: (402) 472-2142. Fax: (402) 472-1693. E-mail: [email protected] 5 Office of the Texas State Chemist. Texas Agricultural Experiment Station. Texas A&M University, College Station, TX 77841-3160. 6 USDA-ARS, Center for Grain and Animal Health Research, Manhattan. KS 66502. Names are necessary to report factually on available data; however. the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. 7 Department of Agronomy and Horticulture. University of Nebraska-Lincoln. Lincoln, NE 68593-0915. doi:10.1 094/CCHEM-06-1 0-0087 © 2010 AACC International, Inc. 524 CEREAL CHEMISTRY crystallinities. Statistically significant (P < 0.05) regression equations showed that com nixtamal moisture content was influenced by TADD (tangential abrasive dehulling device) index. kernel moisture content. starch content. and protein content; sorghum nixtamal moisture content was influenced by starch relative crystallinity. kernel moisture content, and abrasive hardness index. Pericarp removal was not strongly correlated with kernel characterization tests. Location (environmental) and hybrid (genetic) factors influenced most kernel characteristics and nixtamalization processing variables. conditions, grain characteristics such as hardness, kernel composition, and starch properties are also critical (Sahai et aI2001a). Corn and sorghum contain areas of both vitreous and opaquesoft endosperm. The vitreous endosperm is made up of polygonalshaped starch granules tightly packed in a continuous protein matrix with dispersed protein bodies (Hoseney 1994). The opaque endosperm is made up of spherical starch granules loosely packed in a discontinuous protein matrix with no protein bodies (Hoseney 1994). While vitreousness is not synonymous with hardness, increased amounts of matrix protein and protein bodies have been associated with hardness (Chandrashekar and Mazhar 1999). Hardness characteristics of corn and sorghum can be evaluated by measuring grinding performance with the Stenvert Hardness Tester (SHT) (Pomeranz et al 1985), resistance to abrasion with the Tangential Abrasive Dehulling Device (TADD) (Shandera et al 1997; Griess et al 2010), true density with a gas pycnometer, and bulk density by measuring the weight of a known volume of grain. Total protein content and the amount of prolamines (aqueous alcohol-soluble proteins) increase hardness (Chandrashekar and Mazhar 1999). Hardness has been associated with decreased DML and nixtamal moisture content (Pflugfelder et al 1988; Shandera et al 1997; Sahai et al 2001a). Harder kernels are often preferred by processors because they absorb moisture more slowly than softer kernels, resulting in decreased processing variability (Shandera et al 1997). Several researchers have concluded that softer kernels lose less pericarp during nixtamalization, but this relationship has not been definitively established (Serna-Saldivar et al 1991; Shandera et a11997; Salinas et aI2003). Starch content and functionality are important characteristics related to processing performance. Common starch characterization tests include using a Rapid Visco-Analyser (RVA) which measures pasting properties, differential scanning calorimetry (DSC) which measures thermal properties, by enthalpic transitions and X-ray diffraction which is used to measure the relative amounts of crystalline versus the amorphous forms (relative crystallinity) of starch. Sahai et al (1999) concluded that RVA and DSC were useful techniques in determining starch gelatinization properties relating to nixtamalization. In addition to starch gelatinization, DSC gives information about starch polymer associations by measuring the amount of energy required (enthalpy) to disrupt ordered structure (Tester and Karkalas 200 I). Starch crystalline properties, as measured by X-ray diffraction, and thermal stability of structure, as measured by DSC, also are useful in predicting nixtamalization performance (Gomez et al 1989; Sahai et a12001b; Mondragon et aI2004).