The impact of heat-moisture treatment on the molecular structure and physicochemical properties of normal and waxy potato starches

Vamadevan, Varatharajan (2010) The impact of heat-moisture treatment on the molecular structure and physicochemical properties of normal and waxy potato starches. Masters thesis, Memorial University of Newfoundland.

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Abstract

Heat-moisture treatment (HMT) is a physical modification technique that modifies starch structure and properties without destroying its granular structure. HMT has been shown to cause starch chain interactions and crystallite disruption/reorientation within the amorphous and crystalline domains. However, the part played by amylose (AM) during HMT of starches is not properly understood. Furthermore, a systematic study has not been carried out to examine how variations in HMT temperatures influence molecular structure, physicochemical properties and digestibility of normal potato (NP) and waxy potato (WP) starches. Thus, the objective of this study was to determine changes to molecular structure, physicochemical properties and digestibility of NP and WP starches on HMT at different temperatures (80, 100, 120 and 130°C) for 16 h at 27% moisture. Structural changes on HMT were monitored by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), polarized light microscopy (PLM), wide angle X-ray scattering (WAXS), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, fluorophore assisted capillary electrophoresis (FACE) and K/S spectra. Changes to physicochemical properties on HMT were determined by granular swelling, amylose leaching, gelatinization parameters and pasting properties. Digestibility of normal and waxy potato starches before and after HMT by porcine pancreatic α-amylase (PPA) was monitored by measuring initial velocity and by examination of the granular structure at different stages of hydrolysis by SEM, CLSM and PLM. The results showed that structural changes on HMT were influenced by differences in starch chain mobility at different temperatures of HMT. Starch chain mobility, in turn, was influenced by the interplay between the extent to which B-type crystallites were transformed into A+B-type crystallites, kinetic energy imparted to starch chains and amylose content. The main type of structural changes influencing physicochemical properties at different temperatures of HMT were starch chain interactions (at 80 and 100°C), disruption of hydrogen bonds between amylose-amylopectin and amylopectin-amylopectin (at 120 and 130°C), disorganization of amylopectin chains near the vicinity of the hilum (at 100, 120 and 130°C) and formation of interrupted helices (at 130°C). The susceptibility of NP and WP starches towards α-amylase decreased at 80°C, but increased in the range 100 to 130°C. NP and WP starches exhibited heterogeneity in degradation (NP>WP) in both their native and HMT states.

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