Effect of pretreatments and additives on the thermal behavior and hygroscopicity of freeze-dried pineapple juice powder

Pasteurization of pineapple juices at 80C for 5 min in the presence of added acids (citric, malic and fumaric) and cane sugar was found to increase its reducing sugar content from 3.5 to 6.5%, which in turn decreased the glass transition. temperature (Tg) and increased the hygroscopicity of the juice powder Inversion of sucrose could be avoided by adding sugar and acid to a pasteurized cooled juice. Among the acids, citric acid caused 30% more hygroscopicity than malic and fumaric. Incorporation of additives into the juice prior to freeze-drying helped in reducing the hygroscopic tendency of the juice powder. Among the additives tried, trehalose, beta-cyclodextrin and sorbitol were found to be beneficial as they increase the Tg and reduce the hygroscopic tendency of the juice powder.