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Influence of granule heterogeneity on starch functional properties
Abstract
Starch granule structure and functionality in cooked aqueous suspensions, common in foods, is governed by the extent of heat treatment, starch hydration and the inherent chemical and physical properties of native starch granules. It is being recognized that native starch granules are heterogeneous in character. They exhibit unique structure and functionality when subjected to hydrothermal processing. This research was designed to elicit information about heterogeneity in native starch granules and to study granular changes when they were cooked in aqueous suspensions. A reverse flow sedimentation system was designed to fractionate granules on the basis of apparent granule density. Different density fractions of native normal corn starch granules exhibited differences in solubility, as determined by high performance size exclusion chromatography (HPSEC) and granule crystallinity as measured by x-ray diffraction. Starch granule heterogeneity was also observed using Differential Scanning Calorimetry (DSC). DSC endotherms obtained at 10%, 50% and 80% hydration showed substantial differences in endotherm onset, peak and end temperatures. On annealing, however, these differences became insignificant and seem to disappear, suggesting that recrystallization and amylose lipid complex formation did not occur in annealed starch. Mechanically damaged starch granules did not exhibit enthalpic transitions. These results do not confirm the theory that helical melt transition can be followed by a DSC. Heat damaged starch granules could be separated, using reverse flow sedimentation, from a suspension of starch granules heated to 65$\sp\circ$C. The heat damaged fraction exhibited a high degree of susceptibility to enzymatic degradation, and had a high temperature DSC endotherm at 80% hydration, indicating formation of 'V-type' structures. Starch granules heated to 75, 85 and 95$\sp\circ$C, formed gels which were evaluated for textural characteristics by Instron texture profile curves. It was possible to observe minute differences in starch gels heated to 65, 75 and 85$\sp\circ$C, suggesting that changes in granules such as swelling and amylose leaching could be quantified by this technique. Granule remnants or micro-gels, after heating starch (5% aqueous suspension), were extracted and fractionated on the basis of apparent density by reverse flow sedimentation. Micro-gels exhibited differences in apparent solubility in water, when characterized by HPSEC. Understanding the diversity of native starch granule structures, their unique functional and textural attributes arising when hydrothermally processed, may help to unfold the complexity of starch granule structure and functionality in foods.
Subject Area
Food science|Botany
Recommended Citation
Sahai, Deepak, "Influence of granule heterogeneity on starch functional properties" (1994). ETD collection for University of Nebraska-Lincoln. AAI9425307.
https://digitalcommons.unl.edu/dissertations/AAI9425307