Application of different compositions of apple puree gels and drying methods to fabricate snacks of modified structure, storage stability and hygroscopicity

Abstract

The aim of this study was to determine the effect of incorporation of apple puree and maltodextrin to agar sol on the sorption properties and structure of the dried gel. The effect of different drying methods on the sorption behaviour of aerated apple puree gels was also observed. The gels with the addition of 25% and 40% concentration of apple puree and with or without maltodextrin were prepared and dried. The foamed agar gel was subjected to freeze‐drying, air-drying and vacuum‐drying. The sorption properties of dried gels (adsorption isotherms, water uptake in time) were investigated. The relations between the glass transition temperature, water activity and water content were also obtained for some apple snacks. The increase in apple puree in freeze‐dried gels increased the hygroscopicity and decreased the glass transition temperature (Tg). The water content at given activity and hygroscopicity were reduced by the addition of maltodextrin, which also caused the increase in Tg. The application of different drying methods enabled obtaining different structures of material. The open‐pore, fragile materials were obtained by freeze‐drying, the expanded matrix with big holes was characteristic for vacuum‐dried gels, but the closed pores with thick walls were created during the air‐drying.