Effects of ultrasonic pretreatment combined with vacuum drying on the drying kinetics and quality of green peppers
Chunyu Yao, Po Niu, Xiaoqi Ren, Jie Zhou, Yushu Lai, Pan Wang
Abstract
This study examined the effects of ultrasonic pretreatment combined with vacuum drying on the drying rate and quality of green pepper slices, addressing issues like long drying times and low product quality. Results showed that ultrasonic pretreatment significantly shortened drying time, reduced energy use, and improved the samples' physicochemical properties. The best conditions were identified as 150 W ultrasonic pretreatment combined with low-temperature (45-55 °C) vacuum drying. Compared to untreated samples, ultrasonic pretreatment reduced drying time by 11.76%-40.00%, decreased energy consumption by 0.31%-12.02%, and enhanced effective moisture diffusivity, color, rehydration ability, and texture. Among five mathematical models tested, the Logarithmic model best described the drying process of ultrasonically pretreated green peppers under vacuum. Microstructural analysis indicated that ultrasonic pretreatment and drying temperature caused structural changes, creating more micro-pore channels. At 150 W pretreatment, the total color difference decreased by 2.3%-20%, while total phenolic content and vitamin levels increased by 5.88%-8.25% and 8.92%-24.59%, respectively. Temperature was also a key factor: higher temperatures lowered drying time and energy use, but samples kept better quality at 45-55 °C. This research offers solid evidence that ultrasonic pretreatment can improve drying efficiency, product quality, and energy savings during vacuum drying of green peppers.