Sucrose-salt combined effects on mass transfer kinetics and product acceptability. Study on apple osmotic treatments

Apple samples were osmotically treated in different hypertonic sucrose solutions (with or without NaCl) at low-temperatures (18-30 degreesC). Sodium chloride was employed to assess the possibility to increase the process rate without affecting the sensory acceptability of treated fruit. Mass transfer kinetics were modelled according to Peleg equation (1988); kinetic parameters were calculated and modelled, as functions of solutes concentration and processing temperature, using response surface methodology. Salt concentration improved water loss at equilibrium but showed a negative interaction effect with sucrose concentration. Salt and sucrose concentrations had a synergetic effect on soluble solid impregnation, on the other side sugar concentration showed to reduce salt gain. A variation (as function of the considered variables) of a mass transfer parameter at the equilibrium condition, is not always reflected by a similar variation of the mass transfer parameter's initial rate. This fact could be explained by the existence of instantaneous interactions at the food-solution interface. The addition of a level (0.5%) of NaCl determined a reduction of the product accept ability very close to that determined by the addition of a sucrose level (5%). Salt gain was not sufficient to balance the sweetness of the product, but an addition of NaCl may help to attenuate the excessive sweetness of product processed with high sucrose concentration.