Microwave pulsed vacuum drying improves drying efficiency and quality attributes of Cistanche: comparative evaluation...

This study evaluated the effects of microwave pulsed vacuum drying (MPVD) on the quality attributes and bioactive profile of Cistanche, in comparison with freeze drying (FD) and hot air drying (HAD). Four MPVD vacuum pulse ratios, namely 1:1, 3:1, 5:1, and 7:1, were comparatively investigated. MPVD4 achieved the shortest drying time (130 min), whereas among the tested MPVD conditions, MPVD3 (vacuum pulse ratio 5:1) showed a favorable overall balance among drying efficiency, structural preservation, color attributes, and selected bioactive compounds. MPVD3 showed the highest echinacoside content among all treatments and relatively high levels of pectin, total flavonoids, and polysaccharides compared with HAD. Volatile analysis showed that MPVD3 had relatively higher proportions of phenols, aromatic compounds, ethers, and terpenes than FD and HAD, indicating a distinct volatile profile. In vitro digestion showed that MPVD3 improved the retention of echinacoside and acteoside compared with HAD, although FD exhibited the highest post-digestion retention. Untargeted metabolomics revealed that MPVD3 generated a distinct metabolite profile rather than simply reproducing the FD profile, with higher relative abundances of organic oxygen compounds and secondary metabolites than HAD. KEGG enrichment analysis indicated changes in metabolites annotated to phenylpropanoid-related pathways; however, these results should be interpreted as pathway-associated metabolite differences rather than evidence of activated biosynthesis in dried samples. These findings suggest that, among the tested treatments, MPVD at a 5:1 pulse ratio is a promising drying condition for producing dried Cistanche with favorable quality attributes and improved processing efficiency.