# Different drying methods reshape volatile aroma and bioactive non-volatile compounds in Camellia nitidissima flowers and infusions: UPLC-MS/MS and GC–MS insights

## TL;DR

Different drying methods affect the aroma and health compounds in Camellia nitidissima flowers and tea infusions, with vacuum freeze-drying preserving more nutrients and sensory qualities.

## Contribution

This study reveals that vacuum freeze-drying preserves more bioactive compounds and aroma in Camellia nitidissima flowers compared to hot-air drying.

## Key findings

- Vacuum freeze-drying (VFD) preserves higher levels of flavonoids, polyphenols, and lipids compared to hot-air drying (HAD).
- VFD flower infusions show greater diversity and higher concentrations of non-volatile metabolites like anthocyanins and isoflavones.
- VFD flower infusions have higher relative odor activity values for 76 key odorants compared to other drying methods.

## Abstract

Drying is a critical processing step in the production of Camellia nitidissima Chi (CN)-scented tea. We investigated the effects of hot-air drying (HAD) and vacuum freeze-drying (VFD) on non-volatile and volatile compounds in CN flowers and their tea infusions, utilizing mass spectrometry. Both methods reduced CN moisture to below 8% and significantly reduced volatile compound concentrations. VFD-treated flowers exhibited better morphology and higher levels of flavonoids, polyphenols, and lipids, thereby enhancing antioxidant capacity; while HAD promoted the upregulation of stress-related metabolites, such as phenolic acids. Moreover, VFD flower infusion showed greater diversity and significantly higher concentrations of non-volatile metabolites, especially lipids and flavonoids (anthocyanins, isoflavones). 78.3% of differential aroma compounds (VIP > 1) had higher relative odor activity than infusions from fresh and HAD flowers. These results may underscore VFD as the preferred method for retaining both the nutritional and sensory attributes of CN flowers and their tea infusions.

•Hot-air drying (HAD) alters more phenolic acid than Vacuum freeze-drying (VFD).•VFD flowers retain higher total flavonoids, phenolics, and antioxidant capacity than HAD.•Both methods significantly reduce volatile content, but VFD maintains the original profile.•VFD flower infusion has higher lipid, anthocyanin, and isoflavone content than HAD.•VFD flower infusion exhibits higher rOAV for 76 key odorants than other infusions.

Hot-air drying (HAD) alters more phenolic acid than Vacuum freeze-drying (VFD).

VFD flowers retain higher total flavonoids, phenolics, and antioxidant capacity than HAD.

Both methods significantly reduce volatile content, but VFD maintains the original profile.

VFD flower infusion has higher lipid, anthocyanin, and isoflavone content than HAD.

VFD flower infusion exhibits higher rOAV for 76 key odorants than other infusions.