Partial-degradation and heat-moisture dual modification on the enzymatic resistance and boiling-stable resistant starch content of corn starches

Normal corn, Hylon V and Hylon VII starches were partially degraded by acid-ethanol treatment and applied to heat-moisture treatment (HMT) for improving the enzymatic resistance of starch. The weight-average degree of polymerization (DP_w) of acid-ethanol-treated (AET) corn starches ranged from 6.75 × 10⁵ to 181, 4.48 × 10⁵ to 121, and 1.94 × 10⁵ to 111 anhydrous glucose units for normal corn, Hylon V and Hylon VII starches, respectively. Starch retained its granular structure after AET and HMT, recovery of starch granules after modifications were higher than 92%. Resistant starch (RS) content and boiling-stable RS content of corn starch increased after dual modification, and the increment increased with increasing duration of AET. The boiling-stable RS content of dual-modified starch increased from 1.5 to 9.2, 12.2 to 24.1, and 18.0 to 36.2% for normal corn, Hylon V and Hylon VII starches, respectively. Increments of RS content and boiling-stable RS content of dual-modified starches were significantly correlated (r² > 0.700) with DP_w of starch, revealing that the enzymatic resistance of dual-modified corn starch granules increased with decreasing molecular size of starch. Result also suggested that starch granules partially degraded with AET could improve the molecular mobility and ordering during the consequent HMT.     

Formation,characterization, and glucose response in mice to rice starch with low digestibility produced by citric acid treatment

The optimum conditions for producing rice starch enriched in slowly digestible and resistant fractions by citric acid treatment determined by a response surface methodology (RSM) model equation, were: reaction temperature, 128.4 °C; reaction time, 13.8 h; and citric acid, 2.62 mmol/20 g starch. The slowly digestible and resistant starch fractions of the optimally acid-treated rice starch totalled 54.1%, which was 28.1% higher than the control. The slowly digestible and resistant fractions of the acid-treated rice starch did not differ significantly after heat treatment, whereas those of raw rice starch decreased by 49.6–63.8%, depending on the type of heat treatment (cooking at 100 °C or autoclaving). The slowly digestible fraction of the acid-treated starch increased by 8.9–14.2%. After autoclaving, the glucose response of the acid-treated starch was lower than untreated starch, but similar to that of Novelose 330. After heat treatment, the rate of blood glucose decrease was slower for the acid-treated starch than for Novelose 330. Compared to raw rice starch, the acid-treated starch exhibited increases in apparent amylose content, blue value, dextrose equivalent, cold-water solubility and transmittance, and decreases in wavelength of maximum absorbance, viscosity, and gel-forming ability.     

Muffins with resistant starch: Baking performance in relation to the rheological properties of the batter

The effect on baked muffins of progressively replacing wheat flour with resistant starch (RS) was studied. Muffin volume and height and the number and area of gas cells decreased significantly when the RS level reached about 15% (by weight of total formulation) or higher. Rheological properties of the raw batters were studied: the mechanical spectra of batters at 25 °C, the evolution of the dynamic moduli (G′ and G″) with rising temperatures (from 25 to 85 °C) and the mechanical spectra at 85 °C were obtained from oscillatory rheological tests. The decrease in the viscosity and in the elastic properties of the muffin batter as the flour was increasingly replaced by RS was related to the baking performance of the final baked products.     

Characterisation of starch during germination and seedling development of a rice mutant with a high content of resistant starch

To acquire a better understanding of whether RS influences the dynamics of in vivo starch digestion and seed vigour, the high-RS rice mutant RS4 (RS ca. 10%) and the wild type R7954 were used to investigate total amylase activity, seedling vigour, starch content and starch granule structure during germination. RS4 exhibited similar seed vigour to R7954. Amylose and amylopectin in R7954 showed synchronous degradation throughout the whole process, while amylopectin was hydrolysed significantly faster than amylose in RS4 during the earlier germination stages. The starch residues of RS4 after germination (GD) lost endotherm peaks and showed a special X-ray diffraction pattern with only two peaks at around 16.90° and 21.62°, probably due to remnants of amylopectin and its tight crosslinking with the cell wall. The remaining starch after 10 GD, primarily amylopectin may make a critical contribution to total resistant starch content. These results indicated that RS had no negative impact on seed vigour in rice lines, although RS cannot be hydrolysed by α-amylase from human and animal in vitro. By appropriately increasing the special amylopectin fraction, a new breeding programme of high RS crops and improvement in the eating quality of high RS rice varieties might be achieved.     

Thermoplastic starch modified during melt processing with organic acids: The effect of molar mass on thermal and mechanical properties

Thermoplastic starch (TPS) was modified with ascorbic acid and citric acid by melt processing of native starch with glycerol as plasticizer in an intensive batch mixer at 160 °C. It was found that the molar mass decreases with acid content and processing time causing the reduction in melting temperature (T_m). As observed by the results of X-ray diffraction and DSC measurements, crystallinity was not changed by the reaction with organic acids. T_m depression with falling molar mass was interpreted on the basis of the effect of concentration of end-chain units, which act as diluents. FTIR did not show any appreciable change in starch chemical compositions, leading to the conclusion that the main changes observed were produced by the variation in molar mass of the material. We demonstrated that it is possible to decrease melt viscosity without the need for more plasticizer thus avoiding side-effects such as an increase in water affinity or relevant changes in the dynamic mechanical properties.