Constant temperature and humidity combined with vacuum-steam pulsed steaming of Polygonatum cyrtonema rhizome: Quality attribute and browning mechanism

The quality of Polygonatum cyrtonema rhizome is considerably influenced by steaming, a post-harvest procedure; however, the mechanisms behind this quality formation are not well understood. This study explored two innovative streaming methods for Polygonatum cyrtonema rhizome: constant temperature and humidity steaming and drying (CTHSD) and constant temperature and humidity combined with vacuum-steam pulsed steaming and drying (CTH + VSPSD). Traditional atmospheric steaming, simmering, and drying (ASD) were also used. We evaluated the microstructure, colour and polysaccharide, reducing sugar, 5-hydroxymethylfurfural, amino acid, phenolics and diosgenin contents as well as its antioxidant capacity. Results indicated that all methods enhanced antioxidant activity, released phenolic compounds and disrupted the microscopic pore wall structure. The processed samples exhibited increased browning values owing to non-enzymatic browning reactions between amino acids and reducing sugars. Notably, the CTH + VSPSD method yielded the highest antioxidant capacity, better preservation of polysaccharides and lower levels of 5-hydroxymethylfurfural compared to other methods. Additionally, CTH + VSPSD reduced production time by 66.7 % while achieving a comparable colour profile to that of conventional ASD technology. Therefore, the CTH + VSPSD method shows great promise for producing high-quality Polygonatum cyrtonema rhizome products.