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

Abstract

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 (To), peaks (Tp1, Tp2) and final (T1) temperatures decreased linearly with increasing water content. Experimental data were successfully (R2 > 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.