Effect of liquid nitrogen pretreatments on osmotic dehydration of blueberries

摘要

Fresh blueberries are highly perishable and must be preserved by either freezing or drying technologies. However, moisture impermeability of their skin is a barrier against the 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. The number of immersions in liquid nitrogen was a determinant factor that accelerated water loss. Depending on the blueberry species, a reduction of dehydration time from 45% to 65% was obtained for liquid nitrogen treated samples when compared to control blueberries. Microscopic observations of the blueberry skin before and after the liquid nitrogen pretreatment revealed a decrease of the cuticle thickness, dewaxing of the skin surface and the presence of micro-fissures 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 nitrogen pretreatments showed a slight decrease in the levels of phenolic compounds and anthocyanins compared to the fresh blueberries.