CURRENT TRENDS IN DRYING ANDDEHYDRATION OF FOODSDebabandya Mohapatra1 and Sabyasachi Mishra2

ABSTRACTDrying and dehydration techniques have constantly been evolving since ancient time; from sun drying to solar drying, from convective air drying to impingement drying. The heating medium has changed from sunlight to dielectric and electromagnetic radiation, from hot air to jet impingement, from steam to superheated steam etc. Drying essentially is a simultaneous heat and mass transfer process, wherein heating medium or internal heat generation helps in evaporation of free water molecules from the product. Mass transfer rate, during the drying/dehydration process, can be enhanced by different pretreatments, apart from using enhanced temperature, optimum air flow rate in case of convective drying or using high intensity electric field as in case of dielectric and other electromagnetic drying systems however, opting for extreme conditions, product quality may be compromised. To suit the consumer demand for quality product, current technologies are aiming at integrating different pre-treatments like blanching, chemical treatment, physical modification, application of thermal and non-thermal processes, for inactivation of enzymes, reduction in microbial load and structural modification with an aim to enhance mass transfer rate. Enhanced mass transfer rate eventually overcomes the drying cost and deterioration associated with longer drying time. Innovative drying technologies such as refractance window drying, corona air orelectrohydrodynamic drying, super-critical CO2 drying and bio-film drying are trying to address some problems associated with drying. Various hybrid drying technologies that manifest judicious integration of several dehydration techniques such as osmosis, convective, vacuum, microwave, radiofrequency, infrared and ohmic heating and freeze drying with non-thermal processing like high pressure, ultrasound, pulse electric field and irradiation are cost effective, as these methods reduce drying time considerably at the same time maintaining the product quality.Keywords: pre-treatment, hybrid drying, non-thermal processing, electromagnetic heating.