Rheological properties of chestnuts processed by osmotic dehydration and convective drying.

摘要

Effects of osmotic drying using sucrose solutions followed by convective drying were investigated on the rheological properties of chestnuts (Castanea sativa). Prisms of chestnuts (10 x 10 x 15 mm) were immersed into sucrose solutions (60% w/w) for different periods (1, 2, 8 and 24 h) at 25 degrees C. The samples were dried with hot air at 65 degrees C and 30% RH for different times (0, 0.5, 1.5, 3 and 6 h). Finally, the rheological behaviour of chestnuts at different moisture and sucrose contents was determined using a universal machine to carry out mechanical tests. Osmotic drying kinetics were evaluated by measuring sucrose and moisture contents. Sugar gain and water loss increased with operation time. Analysis of drying kinetics revealed higher drying rates during the early stages of the procedure. Rheological data (stress, strain and modulus of elasticity) changed strongly with water and sucrose contents. At high moisture contents, samples with higher sucrose contents showed more ductile properties than samples that had not been subjected to osmotic pre-treatment, and at low moisture contents the presence of sugar led to harder samples.