Influence of sugar composition on water sorption isotherms and on glass transition in apricots

Desorption isotherms of fresh and osmotically treated (70%, 30 degrees C) apricots have been measured at 30,45 and 60 degrees C by the static gravimetric method. A differential scanning calorimeter was used to determine the T-g of samples equilibrated with several water activities. The osmotic pretreatment affected the shape of the desorption isotherms because of biopolymer binding at low activities values and dissolution of sucrose at high activities values. At 45 degrees C, isotherms of fresh and sucrose impregnated apricots are identical. At 60 degrees C, sucrose impregnation depressed water activity, while at 30 degrees C the opposite effect is observed. Evolution of moisture content at the first saturation layer expresses these effects of sucrose impregnation and temperature. Peleg model fitted the best experimental desorption isotherms of the fresh and osmotically treated apricots (0.990 <= r(2) <= 0.999, 0.005 <= S <= 0.045). A strong plasticizing effect of water on the T-g was found, with a great reduction in this value with increase in water activity. (c) 2012 Elsevier Ltd. All rights reserved.