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Understanding corn endosperm morphology through solvent and heat treatments
Corn (Zea mays, L.) kernel structural integrity is based on the associations between endosperm components. This study's purpose was to characterize the physical/chemical properties of kernel endosperm microstructure and the alterations that occur during processing/laboratory research. The functionality of endosperm during dry milling was well predicted (correlation of r > 0.8) with laboratory abrasive/hardness tests. Resistance to abrasion, hardness, percent floaters, and protein content were moderately predictive (r > 0.6) of moisture absorption during alkaline cooling while breakage susceptibility somewhat predicted dry matter loss (r = 0.6). Wet milling characteristics were not well (r < 0.5) predicted by any one test. The low correlations between hardness tests and allmfine processing or wet milling suggests that endosperm component and structure functionality present in the dry endosperm were not predictably conserved or expressed after exposure to solvents and heat during processing. Kernel Instron texture analysis showed that incubation at 20, 40, 55, or 90°C under non-drying conditions or when soaked in acetone did not significantly (p < 0.05) alter fracturability or hardness, but aqueous-based solvents' weakening (dissociation) of endosperm structure was typically temperature and time dependent. Urea's gelatinization of structures was highly time and temperature dependent. Water induced a moderate level of dissociation between endosperm structures, as evidenced by texture analysis and sonication; scanning electron microscopy showed that water's plasticization of components weakened starch-protein bonds. Bisulfite and sodium dodecyl sulfate denatured proteins and enhanced protein-starch dissociations more than water-only soaks. Alkaline (pH ∼12.5) soaks solubilized matrix proteins and produced the greatest dissociation of endosperm structures. Soaking in allcaline or ethanol (70% aqueous) weakened cell wall associations, thus reducing fracturability measurements substantially. Ethanol solubilized protein storage bodies, but did not induce dissociation of intracellular endosperm structures. Endosperm structural integrity is ultimately preserved by hydrogen bonds, disulfide protein linkages, and hydrophobic aggregations. Water (and heat) can be used during processing to plasticize endosperm components and weaken structure; protein solubilizing/denaturing agents further modify endosperm functionality and/or aid in separating endosperm components. Solvents that affect matrix proteins have the greatest impact on structural integrity.
Shandera, Donald Lee, "Understanding corn endosperm morphology through solvent and heat treatments" (2000). ETD collection for University of Nebraska - Lincoln. AAI9967407.