Rakesh Raghunathan - January 8

Hierarchical structure of field pea starches and their impact on physicochemical properties

Presently, there is a dearth of information on the hierarchical structure of field pea starches spanning different length scales. Consequently, it is difficult to explain their functionality. The objective of this study was to isolate starch from four newly released cultivars of field peas (CDC Golden, CDC Amarillo, CDC Patrick and Abarth) grown at Rosthern and Meathpark in Saskatchewan, Canada and to determine their composition, molecular structure and physicochemical properties. The morphology, structure and physicochemical properties of the starches were determined by microscopy, particle size analysis, HPAEC-PAD (High performance anion exchange chromatography with pulsed amperometric detection), ATR-FTIR (Attenuated total reflectance Fourier transform infra-red spectroscopy), WAXS (Wide angle X-ray diffraction), 13C CP/MAS NMR (13C cross polarization magic angle spinning nuclear magnetic resonance), RVA (Rapid visco analyzer), DSC (Differential scanning calorimetry), acid hydrolysis, enzyme hydrolysis and retrogradation. The yield, apparent amylose content, free and bound lipids, specific surface area and diameter ranged from 34 to 37%, 38.2 to 42.6%, 0.06 to 0.15%, 0.8 to 1.7%, 0.31 to 0.38 m2g and 26.6 to 30.5% respectively. Differences in amylopectin chain length distribution among field pea cultivars were not significant. All cultivars exhibited a C-type X-ray pattern. The relative crystallinity and B-polymorphic content ranged from 33.1 to 36.8% and 41 to 55.5%, respectively. Significant differences were observed with respect to the molecular order near the granule surface. The gelatinization transition temperatures were lower and the extent of crystalline homogeneity was higher in CDC Amarillo and CDC Patrick than in the other starches. All starches exhibited similar extent of amylose leaching and granular swelling. There were no significant differences in the extent of acid hydrolysis. The largest difference among cultivars was seen in their pasting parameters. CDC Patrick and CDC Amarillo behaved differently from other starches with respect to lower pasting temperatures, lower peak viscosity, higher thermal stability and higher final viscosity. The results showed that CDC Amarillo and CDC Patrick are better suited for incorporation into foods that are subjected to high temperature processing.

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