Abstract: To elucidate the characteristics of drying kinetics and polyphenol degradation kinetics in the swollen succulent stem of tumorous stem mustard during air-impingement jet drying, the drying was carried out at 40, 50 and 60 ℃. The drying kinetic data were fitted to eight thin-layer drying models. The kinetic characteristics of the degradation of monomeric polyphenols were studied using four reaction kinetics models. The results showed that air-impingement jet drying could result in higher drying efficiency and lighter browning as compared with hot air drying. The drying rate was increased with drying temperature. The Modified Page model could be used to describe and predict the dehydration behavior. Liquid chromatography-mass spectrometry analysis showed that coumaric acid, ferulic acid, narirutin, naringin, hesperidin, lyciferin and hesperidin degraded during the drying process. The degradation of hesperidin, narirutin, lyciferin, pomelin, hesperidin and coumaric acid conformed to second-order reaction kinetics, and seriously affected the antioxidant activity. The degradation of polyphenols taking place during the drying process was a typical nonspontaneous and endothermic reaction. This study provides a theoretical reference for further improving the air-impingement jet drying of tumorous stem mustard.

Key words: tumor stem mustard; air-impingement jet drying; drying characteristics; polyphenols; degradation