Corn is the main component of tortilla chips and must undergo several steps of modification to produce masa dough. Different varieties of corn and the interaction of environmental conditions with post-harvest handling can produce variability in the kernel structure and composition, affecting its functionality in the masa-making process. This study sought to understand how corn composition with processing contributed to the texture of acceptable masa using various rheological and thermal analysis techniques.
TGA analysis illustrated the unique water populations in pericarp, soft endosperm, hard endosperm, and germ during the processing of nixtamalization. Alkaline cooking was the most critical step for increasing the water uptake in all fractions and water became more associated in the pericarp and endosperms. Although germ imbibed water, no increase in water entrapment was displayed following cook. Increase in “freezable water” as observed with DSC also confirmed an increase in bulk water for the four fractions. Soaking only modified the soft endosperm water component to an appreciable degree. Possible thermal shifts between unacceptable and acceptable pericarp and hard endosperm fractions were observed and warranted additional analysis to verify these differences.
Findings from this study narrowed the research focus to the hard endosperm and pericarp fractions in the raw and cook state. Further thermal and rheological analysis was combined with additional testing to characterize the basic composition and material behavior of unacceptable and acceptable corn. Masa adhesion as measured by the TAX.T2 Texture Analyzer, masa moisture quantitated with the Moisture Analyzer, macromolecular composition using near-infrared spectroscopy (NIR), and chemical quantitation of unextractable extensin protein were evaluated. One-way ANOVA
(p < 0.05) established statistical differences between unacceptable and acceptable corn categories while Soft Independent Modeling of Class Analogy (SIMCA) software using Principle Component Analysis (PCA) determined which factors most contributed to the separation of unacceptable and acceptable corn classes.
Results from additional thermal, rheological, and compositional analysis on acceptable and unacceptable corn displayed statistical differences between the two classes. TGA analysis showed a difference in the water populations of raw hard endosperm and pericarp, which may indicate structural variation. Masa adhesion, % protein, and a shift in the onset temperature of a thermal transition in hard endosperm were other important factors distinguishing classes of different corn quality.
Overall, hard endosperm TGA peak temperature and masa adhesion were the greatest distinguishing factors with % protein playing a minor role in classifying corn functionality for nixtamalization. This investigation suggests that a physico-chemical approach may further add knowledge to the regarding the basis of corn functionality for nixtamalization.