Rheological properties of chestnuts processed by osmotic dehydration and convective drying

The effect of osmotic dehydration using sucrose solutions followed by a convective drying on the rheological properties of chestnuts ( Castanea sativa M.) has been studied. Prisms of chestnuts ( 10 x 10 x 15 mm) were immersed into sucrose solutions ( 60% w/w) at different times ( 1, 2, 8 and 24 h) at 25 degrees C. The samples were dried with hot air at 65 degrees C and 30% of relative humidity during different times ( 0, 0.5, 1.5, 3 and 6 h). Finally, the rheological behaviour of chestnuts at different moisture and sucrose content was determined using a universal machine of mechanical tests. Osmotic dehydration kinetics was evaluated determining sucrose and moisture content. Sugar gain and water loss amounts increased with operation time. Drying kinetics analysis showed higher drying rates during first times. Rheological data ( stress, strain and modulus of elasticity) changed strongly with water and sucrose content. At high moisture content samples with more sucrose content showed more ductile properties than no pre-treated osmotically samples and at low moisture content the presence of sugar led to harder samples.