Factors influencing starch chain realignment and interactions within the amorphous and crystalline domains of pulse and high amylose maize starches on annealing

Suntharamoorthy, Maaran (2017) Factors influencing starch chain realignment and interactions within the amorphous and crystalline domains of pulse and high amylose maize starches on annealing. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The composition, morphology, structure and physicochemical properties of starches extracted from lablab bean, navy bean, rice bean, tepary bean and velvet bean were examined. Imaging techniques revealed the presence of cracks on granule surfaces and disorganized starch chains near the vicinity of the hilum in some starches. The starches exhibited wide variations with respect to granular size and specific surface area. Molecular order, molecular orientation (birefringence), double helical content, crystallinity, crystalline perfection and crystalline stability differed among the pulse starches. However, they exhibited similar amylopectin chain length distribution. The results showed that interplay among differences in molecular order, double helical content, relative crystallinity, amylose content, granule morphology and the extent of interactions between starch chains within the amorphous and crystalline domains, influenced thermal, rheological and digestibility properties. The factors underlying the susceptibility of pulse (including wrinkled pea) and Hylon®VII starches toward in vitro hydrolysis were studied. The rate and extent of hydrolysis were influenced by the structure of the native starches at different levels (molecular, supramolecular, granular) of granule organization, and by the extent of interaction among hydrolysed starch chains. Starches were modified by annealing treatment. Annealing increased the relative crystallinity and the onset (To) and melting (Tp) temperatures and decreased the gelatinization temperature range (Tc-To). The increase in Tp and decrease in Tc-To suggest that annealing improved double helix arrangement by decreasing heterogeneity within the crystalline lamellae. This study showed that the organization of starch chains within the amorphous and crystalline domains of native starches influenced reorganization of starch chains on annealing. The extent of these changes differed between normal and high amylose starches due to the structural differences that exist in both amorphous and crystalline regions. The role of amorphous regions on annealing was studied using the approaches of partial acid hydrolysis and cross-linking with sodium trimetaphosphate and sodium tripolyphosphate. The results suggest that the amorphous regions contributed to the molecular mechanism of annealing by influencing the realignment of glucan chains in the crystalline regions.

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