Properties of retrograded and acetylated starch preparations Part 2. Dynamics of saccharification with amyloglucosidase and rheological properties of resulting pastes and gels

Various procedures have been used to produce preparations of retrograded starch, by subjecting it to acetylation with methods used in the food industry. The resultant starch preparations were evaluated for their degree of acetylation through titration, swelling power and solubility in water at 80 °C, and saccharification dynamics as affected by amyloglucosidase. Rheological properties of pastes and gels of native starch and modified starch preparations were characterized with the use of a sweep temperature test as a dependency of the storage modulus (G′) and loss modulus (G″) on temperature. In addition, flow curves of pastes were plotted and mechanical spectra of gels of the preparations examined were determined. These modifications had a significant effect on the preparations produced. Retrograded and acetylated starch preparations were characterized by greater solubility in water and greater swelling power, and were less susceptible to amyloglucosidase than the non-acetylated preparations. Rheological properties of the pastes and gels were affected by the methods of their production. Acetylation was found to significantly affect a decrease in the storage modulus value during heating. Pastes of the native starch and modified starch preparations were characterized by the non-Newtonian flow, shear thinning with a tendency to yield stress. In turn, the mechanical spectra demonstrated that - in the concentration applied - both native starch and modified starch preparation were forming weak gels.     

Properties of retrograded and acetylated starch preparations: Part 1. Structure, susceptibility to amylase, and pasting characteristics

The aim of the study was to produce a retrograded starch preparation from potato starch using various methods, to modify it by acetylation, and then to estimate the effect of these modifications on its selected properties. The chemical structure of modifiers and the degree of substitution achieved with acetic acid were determined by nuclear magnetic resonance (NMR). The resistance of starch to amyloglucosidase and digestive amylases was determined as well. Also, the thermal characteristics of gelatinization of the starch preparations were studied by differential scanning calorimetry (DSC); the method of starch paste production was investigated by a Brabender viscograph, and morphological and structural differences were visualized using scanning electron microscopy (SEM). Retrograded starch preparations were porous and stratified in structure; with their properties resulting from the method of their production. Their chemical structure did not differ from that of native starch, but they displayed a different course of pasting characteristics and increased susceptibility to acetylation as well as resistance to amylases (by approximately 10 g/100 g). Acetylation contributed to a decrease in the temperature of reaching maximum viscosity, an increase in the maximum viscosity, and a decrease in the amount of heat needed for thermal transition of the produced preparations. Acetylated retrograded starch was characterized by a higher degree of substitution and an increased activity of acetyl groups substituted at carbon atoms 2 and 3 compared to the acetylated native starch, thereby triggering a significant increase in resistance to amylases (approximately 40 g/100 g). Combining the resistance of starch samples RS3 and RS4 may be a new method to obtain resistant starch from potato starch.     

细菌纤维素对大米淀粉凝胶老化的影响

为了解细菌纤维素对淀粉凝胶老化的影响,利用快速黏度分析仪、差示扫描量热仪、X-射线衍射和扫描电镜测定添加不同量细菌纤维素的大米淀粉凝胶糊化特性、热力学特性、结晶性和微观结构。结果表明,随细菌纤维素添加量的增加,大米淀粉糊化时崩解值、回生值、糊化焓值显著降低,显示细菌纤维素抑制了大米淀粉凝胶的短期老化;随细菌纤维素添加量的增加,大米淀粉凝胶老化焓值显著降低,而重结晶从13.26%降至7.93%,说明细菌纤维素抑制了大米淀粉中支链淀粉的重结晶;大米淀粉凝胶微观结构显示细菌纤维素的添加使大米淀粉凝胶的表面更加完整、结构更加致密。由此表明细菌纤维素对大米淀粉凝胶老化具有显著的抑制作用。     

Fractal analysis of the retrogradation of rice starch by digital image processing

The surface profiles of retrograded rice starch (RS) samples stored at different times were obtained by horizontal sectioning and scanning electron microscopy (SEM). SEM images showed that the surface topography of the retrograded RS samples possessed fractal characteristics, which was also proven by fractal analysis. The fractal features for analysis were extracted using a new image processing method. The average fractal dimensions of the retrograded RS samples stored for 1, 5, 10, and 15 days were 1.6587, 1.7333, 1.7807, and 1.8340, respectively. The method indicated that the fractal dimension increased as the extent of retrogradation increased. The good correlation between fractal dimensions and the retrogradation enthalpies of the retrograded samples were established using a fitted binomial model (R² = 0.9976). These results show that the fractal dimensions obtained using this new image processing method could effectively quantify the extent of retrogradation.     

Starch retrogradation determined by differential thermal analysis (DTA)

Differential thermal analysis (DTA) as a novel approach to monitor retrogradation degree of rice starch was investigated in this study. Our results found that the onset temperature (To), the peak temperature (Tp), and the conclusion temperature (Tc) were slightly reduced for the retrograded starch, while the differential temperature (ΔT) was significantly increased with the increasing of storage time (P ≤ 0.05). Based on the measurement of the ΔT, retrogradation degree (DR) of rice starch was evaluated, and it was compared with the data collected from the DSC. The result indicated that there was no significant difference in DR obtained from the two analytical methods, although the DR determined from the DTA was slightly higher than that from the DSC. These findings suggest that the DTA as well as the DSC is suitable for the measurement of starch retrogradation.     

Influence of xyloglucan on gelatinization and retrogradation of tapioca starch

Dynamic and steady shear rheometry and differential scanning calorimetry (DSC) were used to investigate effects of xyloglucan (XG) on gelatinization and retrogradation of tapioca starch (TS). The viscosity of TS/XG pastes immediately after gelatinization increased with increasing XG content at the total polysaccharide concentration of 3.5%. Gelatinized TS alone showed pseudoplastic flow at low shear rates and dilatant behavior at higher shear rates (about >1 s⁻¹), while mixtures with XG did not show dilatancy. Mechanical spectra of TS pastes containing XG were more liquid-like than those of TS pastes without XG. XG provides shear stability to the TS during storage. Increases in dynamic moduli during storage at 5 °C were suppressed in the presence of XG. In contrast, the retrogradation ratio determined based on DSC increased more rapidly in the presence of XG. These results suggest that XG forms a continuous liquid phase in a mixture to impart better mechanical stability during storage but to accelerate re-ordering of starch polysaccharides by effectively reducing the amount of water available for starch.