Catalytic infrared blanching and ultrasound sequential synergistic pretreatment on osmotic dehydration of blueberry

Abstract

This study investigated the effects of catalytic infrared blanching, ultrasound, and their combined pretreatments on the dehydration of blueberries. The results showed that catalytic infrared blanching for 6 min facilitated the retention of total phenols and total anthocyanins after the osmotic dehydration of blueberries. The polyphenol oxidase relative enzyme activity and hardness were reduced, while the brightness and relative conductivity were increased. Moreover, the solid gain and water loss were significantly increased with the combined pretreatment of catalytic infrared blanching and ultrasound (60, 40, and 40 + 60 kHz). Reducing the contact angle (from 120.8° to 63.5°) may strengthen the ultrasound cavitation. Furthermore, the drying rate, bioactive components, antioxidant capacity, and color of dried blueberries were evaluated. Compared to the control, the retention of total anthocyanin and the brightness increased. Catalytic infrared blanching combined with ultrasound pretreatment was a processing method to improve the osmotic dehydration efficiency of blueberries. This article deals with osmotic dehydration, a method that partially removes water from blueberries. Ultrasound is considered an effective pretreatment for enhancing mass transfer during osmotic dehydration. The waxy coating on the fresh blueberry epidermis, however, greatly reduces the cavitation effect of ultrasound due to an air film between the epidermis and the solution. Catalytic infrared blanching reduces the hydrophobicity of the epidermis. Catalytic infrared bleaching not only inactivates the enzyme activity in blueberries but also reduces the hydrophobicity of the blueberry skin. In this study, catalytic infrared bleaching was first combined with ultrasound for pre-penetration pretreatment of blueberries, which effectively improved water loss and solids increment during the penetration process as well as enhanced retention of blueberry anthocyanins. Highlights CIB reduced the PPO relative enzyme activity and the contact angle. CIB combined with US significantly increased WL and SG. CIB or US pretreatment improved the retention of TAC, TPC, and TFC.