Enhancing Microwave-Assisted Vacuum Freeze-Drying Efficiency and Quality of Pineapple Slices Through Osmotic Dehydration and Ultrasonic Pretreatment

This article investigates the use of osmotic dehydration and ultrasonic pretreatment to improve the efficiency of vacuum freeze-drying (FD) and microwave-assisted vacuum freeze-drying (FD-VMD) methods. The study examines the influence of pretreatment time, osmotic solution concentration, and ultrasonic power on the moisture content of the pineapple samples. The results show that osmotic dehydration pretreatment can reduce moisture content and weight by up to 15.2% and 8.36%, respectively, while increasing sugar content by 7.5°Bx. Ultrasonic pretreatment is even more effective, with moisture content and weight decreasing by up to 37.5% and 19.45%, respectively, and sugar content decreasing by 4.1°Bx. The FD process shows no significant difference in moisture curve between pretreated and untreated samples, but the pretreated samples have a lower initial moisture content, leading to a potential 35.01% reduction in drying time. The study also evaluates the quality of the dried samples using eight performance indicators, finding that osmotic dehydration pretreatment improves sugar content, crispiness, and flavor, whereas ultrasonic pretreatment enhances rehydration rate, reduces final moisture and sugar content, and results in a softer texture. Additionally, pretreatment significantly reduces drying time and energy consumption, particularly ultrasonic pretreatment with a 120 W power and 40-min duration, significantly reduces drying time and energy consumption by up to 30.02%. These findings demonstrate the positive impact of pretreatment on the energy efficiency and quality of pineapple slices under the FD-VMD process.