Cryogenic pretreatments of blueberries: impact on omsotic dehydration and quality
Authors: Ratti, C, M Ketata, Y Desjardins
Description: Moisture impermeability of blueberry skin is a barrier against moisture diffusion slowing down the drying process. The aim of this study was to investigate the impact of liquid nitrogen pretreatments on osmotic dehydration kinetics of two blueberry species, Vaccinium corymbosum L. and Vaccinium angustifolium Ait, and on the physicochemical quality of dehydrated fruits. Whole blueberries were thus pretreated with 1 to 3 immersions in liquid N2 prior to osmotic dehydration for up to 8 hours in a sucrose solution (60oBrix, 40oC). Non-treated blueberry samples were used as control. Water loss and sugar gain were followed during osmotic dehydration. Microscopy (light and electronic scanning) assessment and wax quantification of the blueberry skin were performed before and after the liquid nitrogen pretreatments. Retention of phenolic compounds and anthocyanins after osmotic dehydration was also measured. The number of immersions in liquid nitrogen was a main factor that accelerated kinetics of water loss. Depending on the blueberry species, a reduction of dehydration time up to 65% was obtained for liquid N2 treated samples when compared to control blueberries. Microscopic observations of the blueberry skin before and after the liquid N2 pretreatment revealed a decrease of the cuticle thickness, dewaxing of the skin surface and the presence of micro cracks facilitating moisture and sugar transfer during the osmotic process. The dewaxing of the blueberry skin due to liquid nitrogen immersions was confirmed by wax quantification before and after the cryogenic pretreatments. Osmotic dehydration and liquid N2 pretreatments showed a slight decrease in the levels of phenolic compounds and anthocyanins compared to the fresh blueberries.
Keywords: cryogenic pretreatments, osmotic dehydration, blueberries, microscopy, mass transfer
Technical field: technical_fields_app4
Session name: Food and bioprocess engineering