Effect of ultrasound-assisted osmotic dehydration pretreatments on drying and quality characteristics of pulsed fluidized bed microwave freeze-dried strawberries

Abstract

In order to improve the shortcomings of low heat and mass transfer efficiency and uneven heating of freeze-drying technology, microwave heating and pulsed fluidized bed technology have been introduced, and ultrasonic-assisted osmotic dehydration (USOD) has been used for pretreatment of strawberries in this study. Using different ultrasonic power (180W, 240W, 300W) and different osmotic sugar solutes (sucrose, trehalose, sucrose and maltodextrin combination) to pretreat strawberries, and determine the dielectric properties, mass transfer, and water status and distribution of strawberries. The drying performance is evaluated by the drying rate, and the drying quality is determined by the color, texture, and total polyphenols and total flavones content. It was found that compared with freeze-drying, pulsed fluidized bed microwave freeze-drying (PFBMFD) can reduce the drying time by 45%, while USOD treatment helps to further increase the drying rate and reduce drying time by 10% because it increases water loss. In addition, dried strawberries pretreated with USOD may have better texture and nutritional quality, and sugar with low hygroscopicity and low sweetness value is more suitable for the USOD process of strawberries.