Quality analysis and pectin characteristics of winter jujube processed by microwave coupled with pulsed vacuum drying (MPVD)

The research aims to investigate the impact of microwave coupled with pulsed vacuum drying (MPVD) at different pulsed vacuum ratios on the drying characteristics and pectin properties of winter jujube, in comparison with freeze drying (FD) and hot air drying (HAD). The drying kinetics, bioactive substances, antioxidant capacity, physical properties, and pectin characteristics were analyzed. Compared to HAD, MPVD-dried samples exhibited significantly reduced drying time by 74.1-81.4%. MPVD and FD samples demonstrated higher rehydration ability, bioactive compound contents, and antioxidant capacity. Furthermore, when using a vacuum pulse-ratio regulation (PR) of 3 (90 s on, 30 s off), along with a microwave power of 250 W (5 W·g-1), the highest drying rate was achieved while maintaining higher retention rates of total phenols, flavonoids, polysaccharides, and cell wall pectin content closer to that of FD sample. Water soluble pectin (WSP) was found to the predominant pectin in jujube, and the WSP and chelate-soluble pectin (CSP) content were positively corelated with the total phenols and flavonoid, while the content of CSP and carbonate-soluble pectin (NSP) shows a positive correlated with the hardness and crispness. These findings indicated that MPVD was an efficient method for getting dehydrated jujube products with high quality.