Rheological properties of extracellular polysaccharide, Pestan, produced by Pestalotiopsis sp

Effect of Hydrocolloids on the Retrogradation of Lotus Seed Starch Undergoing an Autoclaving-Cooling Treatment

The retrogradation properties of lotus seed starch (LS) blended with the hydrocolloids arabic gum (AG), carrageenan (CG), guar gum (GG), and xanthan (XN) were investigated undergoing an autoclaving-cooling treatment, a model for starch retrogradation acceleration. Compared with LS alone, LS-AG showed the increases in syneresis, tan δ (more solid-like behavior), bound water content and immobile water content, molecular weight, the intensity at 480 cm^-1 in Raman spectra and the ratio of absorbance 1047 cm^-1 /1022 cm^-1 (R_1047/1022 ) in FT-IR spectra. The results suggested that the addition of AG tended to promote the starch retrogradation, which was related to the increased molecular migration of free water, interactions of molecular starch chains, and the formation of ordered structures. The addition of CG, GG, or XN significantly decreased the syneresis, tan δ, the intensity at 480 cm^-1 , and R_1047/1022 values of LS, indicating the prevention of LS retrogradation. The effects of CG and XN on starch retrogradation mainly resulted from competition for water and the increased viscosity, as well as the coating effect on starch. The dominant viscosity of GG was the main factor that influenced starch retrogradation. These results showed not all hydrocolloids would retard starch retrogradation under autoclaving-cooling treatment, for which fine structures altered by different hydrocolloids were the key factors. PRACTICAL APPLICATION: Effects of hydrocolloids on the retrogradation of lotus seed starch were investigated undergoing an autoclaving-cooling treatment. The results will help guide the production and development of starchy foods having desirable properties by specific hydrocolloids during autoclaving-cooling process, especially to control starch retrogradation.

Dynamic light scattering of xanthan gum biopolymer in colloidal dispersion

The dynamical properties of nanogels of xanthan gum (XG) with hydrodynamic radius controlled in a size range from 5 nm to 35 nm, were studied at the different XG concentrations in water/sodium bis-2-ethylhexyl-sulfosuccinate (AOT)/decane reverse micelles (RMs) vs. mass fraction of nano-droplet (MFD) at W = 40, using dynamic light scattering (DLS). The diffusion study of nanometer-sized droplets by DLS technique indicated that enhancing concentration of the XG polysaccharide resulted in exchanging the attractive interaction between nano-gels to repulsive interaction, as the mass fraction of nano-droplets increased. The reorientation time (τr ) of water nanodroplets decreased with MFD for water-in-oil AOT micro-emulsion comprising high concentration (0.0000625) of XG. On the other hand, decreasing concentration of biopolymer led to increasing the rotational correlation time of water nanodroplets with MFD. In conclusion, a single relaxation curve was observed for AOT inverse microemulsions containing different XG concentrations. Furthermore, the interaction between nanogels was changed from attractive to repulsive versus concentration of XG in the AOT RMs.