Establishment of Lower Hygroscopicity and Adhesion Strategy for Infrared-Freeze-Dried Blueberries Based on Pretreatments Using CO2 Laser in Combination with Ultrasound

Abstract

The present study aimed at solving industrial problems of hygroscopicity and adhesion of freeze-dried crisp-texture blueberries without adversely affecting the other properties. CO2-based laser in combination with ultrasound-assisted infusion of soybean protein isolate (SPI) prior to pulse-spouted infrared freeze drying (PSIRFD) was noted to be effective in solving this major problem through the results of dynamic water adsorption analyzer. The main reason why this approach worked was that laser pretreatment reduced the exposure of fruit contents (e.g., sugar, organic acid) outside the epidermis. Also, SPI interacted with the fruit contents to reduce the number of hydrophilic points under the synergistic effect of laser and ultrasound by differential scanning calorimetry, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis. What is more, the sample prepared by this method possessed the better physicochemical properties and lower energy consumption. So, CO2-based laser in combination with ultrasound along with PSIRFD represents an attractive alternative for producing high-quality dried blueberries.