Effect of infrared radiation-hot air (IR-HA) drying on kinetics and quality changes of star anise (Illicium verum)

The study aimed to investigate the effects of infrared radiation-hot air (IR-HA) drying on kinetic models and aroma quality of star anise (Illicium Verum). Different temperatures (60 °C, 70 °C, and 80 °C) of IR-HA drying treatments were conducted. Results showed that IR-HA drying increased the drying rates (DR) and the effective moisture diffusion coefficient (Deff). IR-HA drying decreased activation energy (Ea) effectively. The Ea value of the process decreased from 33.84 kJ·mol−1 (HA drying) to 31.57 kJ·mol−1 (IR-HA drying). Four thin-layer drying models were used for describing the drying process of star anises, and the Page's model was the best for fitting the drying data. Besides, star anises processed by IR-HA drying were evaluated to present the higher richness of aroma, higher trans-anethole content, better surface color but worse appearance than the HA drying one. The retention of volatile oil (8.86%) and trans-anethole contents were the highest at 70 °C IR-HA drying. Furthermore, the richness of aroma, spice, wood, sweet, sour, and burnt smells presented significant correlations with the contents of volatile oil and characteristic, trans-anethole, α-bergamotene, linalool, limonene, and △3-carene respectively.