Effect of cold plasma synergistic ultrasound-assisted enzyme treatment on the improvement of hygroscopicity and quality characteristics of jujube powder

Abstract

This study aimed to obtain high-quality jujube powder by reducing its hygroscopicity and tendency to agglomerate. Jujube slices were pretreated with enzyme treatment (EZ), ultrasound-assisted enzyme treatment (US-EZ), cold plasma-assisted enzyme treatment (CP-EZ), and a combined cold plasma synergistic ultrasound-assisted enzyme treatment (CP-US-EZ) prior to vacuum microwave drying (MVD). Given that glucose and fructose are key contributors to hygroscopicity and caking, the impact of each pretreatment on the desugarization effect, nutritional quality, and physical properties of the resulting powder was evaluated. All four pretreatments effectively reduced sugar levels and decreased the agglomeration phenomenon, with CP-US-EZ showing the most pronounced effect. Structural analysis via scanning electron microscopy (SEM) and X-ray diffraction revealed that CP and US modified the powder microstructure, promoting the formation of microporous, spongy textures that facilitated sugar removal and slowed down the hygroscopicity. CP-US-EZ-treated powder exhibited the lowest hygroscopicity and highest contact angle, indicating enhanced resistance to moisture uptake and hydrophobicity. This group showed the greatest content of total phenolics, flavonoids, vitamin C, antioxidant capacity, and monophenols, including 3,4-dihydroxybenzoic acid, protocatechualdehyde, and rutin. These findings demonstrate that CP-US-EZ is a promising non-thermal pretreatment technology to solve the hygroscopicity problem of the powder and produce high-quality, low-sugar jujube powder.