Osmotic dehydration (OD) is a process of soaking products in an aqueous solution containing salt or sugar, which is normally applied to fruits and vegetables. The combination of OD pretreatment with freezing, or osmotic dehydrofreezing (ODF), is a novel technology to shorten the freezing process and prolong the preservation of fruits and vegetables. However, the effectiveness of ODF is affected by process parameters and nature of the product, thus information on freezing characteristics and quality of osmotically dehydrated frozen fruits and vegetables is useful to the food industry. This review intends to provide an overview of the effects of OD pretreatment on freezing characteristics such as freezing rate, thermal properties, and quality of frozen fruits and vegetables. Fundamentals of ODF technology, including significance of OD to freezing, and mechanism and factors affecting ODF are summarized. In addition, hurdle technologies comprising of ODF and other innovative nonthermal techniques, such as ultrasound and pulsed electric field (PEF) are presented, and future trends of the combined technology are briefly discussed. ODF can accelerate the freezing process and enhance the quality of osmotically dehydrated frozen fruits and vegetables. The novel ultrasound and PEF techniques, which can provide cryoprotection from in situ interference, were proposed for the production of product with many‐functional characteristics, by incorporating bioactive compounds like plants sterols, probiotics, and dietary fibers, into the matrix of cellular tissues during ODF process. However, these techniques can enhance the performance of the ODF to promote fast freezing, produce small ice crystals, and raise glass transition temperature of cellular tissues. The future trends of ODF technology should mainly focus on controlling the mass and heat transfer processes, improving quality stability during glassy state storage condition and development of product with many‐functional characteristics.
Practical Applications
Fruits and vegetables are subject to freezing damage, particularly tissue softening and drip loss when thawing, thus reducing their quality and market value. OD pretreatments to freezing or ODF has great potentials in preservation of fruits and vegetables, with the advantage of minimum quality loss due to the reduction in freezing loads. Currently, innovative studies have been carried out on the combined use of OD pretreatments and emerging freezing techniques to improve the freezing process, achieve better quality with extended shelf life, and produce products with many‐functional characteristics. However, the findings presented in this review work can provide detail insights on the quality of fruits and vegetables that were frozen by ODF and give some guidance for further developments of ODF technology.
