Li Guo

Morphologies and gelatinization behaviours of high-amylose maize starches during heat treatment

The granule morphologies and gelatinization behaviours of high-amylose maize starches during heating treatment were investigated by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Maltese crosses demonstrated that the high-amylose maize starches maintained a granular structure even at 120°C. The granules of high-amylose maize starches swelled slightly at 100°C and swelled remarkably at approximately 120°C. The destruction of the starch structure began at the centre and expanded rapidly to the periphery. The intense fluorescence of high-amylose maize starch granules gradually became feeble, and the darker region spread outward during heating at 130°C for 30min, indicating that the amylose component may have been damaged and shifted. The starch granules treated at 140°C were substantially destroyed, and the CLSM, normal light microscopy (NL) and SEM images displayed no discernible granules, which indicated that the original starch granules formed a continuous integrated matrix.

Susceptibility of glutinous rice starch to digestive enzymes

To understand the susceptibility of glutinous rice starch to digestive enzymes and its potential impact on glycemic response, enzyme kinetics and in vitro digestibility of the native and gelatinized starches were investigated. The results showed that the Km values of the native and gelatinized starch were 10.35 mg/mL and 9.92 mg/mL, respectively. The digestion rate coefficients k values of the native and gelatinized starches were 2.0 × 10(-3)min(-1) and 1.1 × 10(-2)min(-1), respectively. The contents of rapid digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) in native glutinous rice starch were 8.92%, 21.52% and 69.56%, respectively. After gelatinization, the amounts of RDS, SDS and RS were 18.47%, 29.75% and 51.78%, respectively. The native and gelatinized glutinous rice starches were 10.34% and 14.07% for hydrolysis index (HI), as well as 43.14% and 45.92% for glycemic index (GI), respectively. During the in vitro digestion, the crystallinity of native glutinous rice starch was increased from 34.7% to 35.8% and 38.4% after 20 and 120 min, respectively.

Compatibility studies on tea polysaccharide/amylose/water and tea polysaccharide/amylopectin/water

The compatibilities of amylose/tea polysaccharide (Am/TPS) and amylopectin/tea polysaccharide (Ap/TPS) in water were investigated with theoretical calculations and experimental measurements. To achieve this, dilute-solution viscometry (DSV) and high-speed differential scanning calorimetry (hyper-DSC) were used. The compatibility criteria on the basis of Δb(m), ΔB(m), μ, Δ[η](m) and thermodynamic parameters, T(g) and ΔT(g) were estimated. The data obtained from DSV show that the Am/TPS mixtures with 0.65:0.35, the Ap/TPS mixtures with (a) 0.85:0.15 and (b) 0.75:0.25 at limited moisture are completely miscible. The results were also confirmed using DSC. A texture analyzer was also used to study effects of Am/TPS and Ap/TPS with different weight fractions on the textures of mixed sol. The results show that the firmness, consistency, cohesiveness and index of viscosity of the Am/TPS and Ap/TPS sol increase with the increase of TPS level and that TPS could provide a more desirable physical structure for starch-based foods.

Investigation of glycerol concentration on corn starch morphologies and gelatinization behaviours during heat treatment

The effects of various glycerol concentrations (0%, 5%, 10%, 20%, and 50%, w/w) on the morphologies and gelatinization behaviours of corn starch were evaluated by confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and rapid visco-analyzer (RVA). When corn starch granules with no added glycerol were treated at 65°C, the granules of corn starch were almost completely broken and tightly connected, and the characteristic birefringence of the starch granules disappeared. Various microscopic techniques revealed that starch gelatinization was delayed to higher temperatures as the glycerol concentration increased. In the presence of glycerol-water systems (5%, 10%, 20%, and 50%, w/w), the peak temperatures of corn starch increased by 1.6°C, 7.4°C, 10.7°C, and 19.7°C, respectively, compared to corn starch in water. The RVA pasting profiles showed that the gelatinization temperature increased as the glycerol concentration increased, which was consistent with polarized light microscope observations and DSC tests.