Improving drying efficiency and product quality of Stevia rebaudiana leaves using innovative medium-and short-wave infrared drying (MSWID)

The effects of hot air impingement drying (HAID), hot air drying with temperature and humidity process control (HADTHPC), medium-and short-wave infrared drying (MSWID), shade drying (HD) and sun drying (SD) on the drying characteristics and physicochemical quality of Stevia leaves were investigated, MSWID was screened out most suitable for Stevia leaves drying. The relationships among drying time, microstructure, color and nutrients retention were analyzed. Compared with other drying methods, MSWID significantly reduced drying time by 15.38% and better preserved the nutrients (steviol glycosides and chlorogenic acids) due to the formation of a distinct microporous structure. Moreover, medium wave infrared (MIR) drying was superior to short wave infrared (SIR) in retaining steviol glycosides and color and improving drying efficiency. Brightness and greenness of dried Stevia leaves were significantly correlated with glycosides and chlorogenic acids content, respectively. MIR at 60 °C is recommended as the most suitable drying conditions due to the highest comprehensive score (0.723) considering drying time, energy consumption and quality. Overall, MSWID is a promising drying technology for realizing high-quality and efficient industrial production of Stevia leaves. • Chlorogenic acids in dried Stevia leaves were maximally retained at 40 °C. • MIRD exhibited better steviol glycosides and color retention than SIRD. • MIRD spent the shortest drying time due to the formation of micropores. • Color parameters were correlated with steviol glycosides and chlorogenic acids. • MIRD at 60 °C was optimum according to efficiency and quality of Stevia leaves.