Effect of water and guar gum content on thermal properties of chestnut flour and its starch

Thermal properties of chestnut flour and chestnut starch at several water content (40, 50, 60 and 95%, flour basis, f.b.) as well as the influence of guar gum (0.5, 1.0, 1.5 and 2.0%, f.b.) on both raw materials at fixed water content (50%, f.b.) were determined by differential scanning calorimetry (DSC). Thermal properties of guar gum-water systems at several guar content (0.5, 1.0, 1.5 and 2.0%, w/w) were also obtained by DSC. Results indicated that the water content and the presence of guar gum had a significant impact on the thermal properties of chestnut flour and its starch. For each endothermic curve, the values of onset (T-o), peaks (T-p1, T-p2) and final (T-1) temperatures decreased linearly with increasing water content. Experimental data were successfully (R-2 > 0.997) described following the Flory equation. A reverse trend was observed in the enthalpy values. Thermal properties of chestnut flour and chestnut starch were suppressed by the presence of guar gum even at the lowest concentrations employed (0.5%, f.b.). The guar gum addition to the assayed systems promoted a starch gelatinization delay and the enthalpy values showed a threshold content above 1.0% of guar gum. Analyses of aqueous guar gum mixtures showed that the existence of a second transition in chestnut starch systems can be successfully explained by means of hydrocolloid-starch interactions, whereas in the flour other interactions should be taken into account. (c) 2013 Elsevier Ltd. All rights reserved

Surface tension and refractive index of guar and tragacanth gums aqueous dispersions at different polymer concentrations, polymer ratios and temperatures

Surface tension and refractive index of guar gum (GG) (up to 0.97% w/w) and tragacanth gum (TG) (up to 1.41% w/w) aqueous dispersions were determined for systems with only one and both gums (mixtures) (up to 1.25% w/w). Experimental determinations were carried out from 5 to 30 C for surface tension and from 10 C to 40 C for refractive index. For mixtures, the effect of polymer ratio (1:3, 1:1 and 3:1) was analyzed at different total gum concentration and temperature. GG showed lower surface activity and refractive index than TG at the same experimental condition. Models for the estimation of surface tension and refractive index as function of gum concentration and temperature were proposed and satisfactorily tested. Both physical and optical properties, in the tested gum concentration range, allowed the determination of different behaviour for both gums because of a critical aggregation concentration for TG dispersions while this phenomenon was not observed for GG.FEDER - CTQ 2010-15309/PPQMinisterio de Educación y Ciencia of Spain - FPU (AP 2007-04397

Drying kinetics of biofilms obtained from chestnut starch and carrageenan with and without glycerol

Drying kinetics of biofilms from chestnut starch and hybrid carrageenan were experimentally determined and modelled. The biofilms were obtained by mixing the respective solutions (4.0% w/w) of both substances in the proportion 80/20 of chestnut starch/hybrid carrageenan. Glycerol (at 5.0% w/w) was added to some biofilms. Biofilms were prepared using a casting method. Drying kinetics were performed at 30, 40, and 50 C for forced air convection (1.8 0.1 m/s) and 30 and 50 C for natural convection. Constant drying rate period, above critical moisture content (5.4 and 4.2 kg water/kg d.b. without and with glycerol, respectively) allowed the evaluation of the heat transfer coefficients. The water diffusion coefficients were determined in the falling rate period assuming a semi-infinite slab with variable thickness. Water sorption isotherms of biofilms at 25 C were determined and fitted with the GAB model. Mechanical properties of different biofilms showed no significant differences for Young’s modulus values (44.0 4.6 MPa). Nevertheless, films prepared at 30 C under natural drying showed the lowest values of tensile strength and elongation (32.2 4.9MPa and 0.85 0.11%).The authors acknowledge the financial support of Ministerio de Educacion y Ciencia (Spain) and Conselho de Reitores das Universidades Portuguesas (Portugal) through a Spain-Portugal integrated action (HP2007-0057 and E30/08)