Thermal analysis and rheological properties of portuguese nut starches isolated by alkali and enzymatic methods

摘要

The search for new sources of starch to be used in industrial products is increasingly demanded. The thermal and rheological properties of starch from chestnut (Castanea sativa Mill.) varieties Martainha and Longal, and acorn (Quercus rotundifolia and Quercus suber Lam.) fruits isolated by alkaline and enzymatic methods were studied. The isolation methods induced changes in those properties. Thermal analysis revealed that the chestnut and acorn starches easily suffer endothermic transition phenomena, showing low onset temperature and enthalpy values, and this is more evident in starches isolated by enzymatic method. In spite of this, the activation energy was high, mainly for starches isolated by A3S method; with Longal starch presenting the low values. Pastes showed viscoelastic behaviour, with a predominance of elastic property, forming strong gels after cooling. For chestnuts, Longal, and for acorns, Q. suber starches were shown to be less resistant to the effect of isolation method. In general, starches isolated by the alkaline method presented the best functional properties as food ingredient.