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Functional properties of corn starch polymers based on their molecular weight and structural characteristics
Abstract
There is now substantial evidence that starch functionality is governed by the molecular structure, size, and weight of starch's amylose and amylopectin components. However, structure-function relationships have not been well established. In this study, four corn starch-types ($<$1, 25, 50, 70% amylose) were separately treated using a combined aqueous leaching and alcohol precipitation technique to produce several different amylose and amylopectin fractions. The fraction's z-average (M$\rm\sb{z}$), weight-average (M$\rm\sb{w}$), and number-average (M$\rm\sb{n}$) molecular weight, polydispersity, and structural attributes such as chain length (degree of polymerization-DP) and branching ratios were monitored by high performance size exclusion chromatography and multiple angle laser light scattering (HPSEC/MALLS). Crystalline patterns were monitored by X-ray analysis. Functional attributes such as retrogradation, pasting, and gel strength were also monitored using differential scanning calorimetry, rapid viscoanalysis, and textural profile analysis, respectively. Relationships between the structures and functional properties were subsequently established. Amylose M$\rm\sb{w}$ was correlated with DP, and both parameters influenced pasting and gelling properties. Amylopectin M$\rm\sb{w}$ was correlated with DP for short branched chains that were predominant in regular and waxy corn starches. In turn, DP was inversely proportional to percent crystallinity. These three molecular factors greatly governed amylopectin pasting, gelling, and retrogradation behavior. Regardless of their branch ratio differences, high to intermediate M$\rm\sb{w}$ (4.89-1.36E + 05) amylose fractions containing chains with DPs of 500-864 and 0-1 branch points per 1000 glucose units, had higher set back and final viscosity values, and resulted in firmer gels than their higher and lower M$\rm\sb{w}$ counterparts. Amylopectin fractions of intermediate to low (8.98-7.08E + 07) M$\rm\sb{w}$ with branching ratios $>$1.5, short branched chains (DP 15-18), and high percent crystallinity ($>$28%) had high peak temperatures, lower peak viscosities, less shear thinning, and higher setbacks than high M$\rm\sb{w}$ amylopectin. Upon cooling, they formed weak gels, but during storage, these gels firmed and retrograded more than those of their high M$\rm\sb{w}$ counterparts. This research strongly indicates that molecular weight and branching characterizations possess potential for predicting some functional aspects of corn starch, and therefore, may also assist in establishing relationships between the structure and function of other starches.
Subject Area
Food science
Recommended Citation
Mua, John-Paul, "Functional properties of corn starch polymers based on their molecular weight and structural characteristics" (1996). ETD collection for University of Nebraska-Lincoln. AAI9623632.
https://digitalcommons.unl.edu/dissertations/AAI9623632