Moisture Transformation and Quality Analysis of Star anise During Hot Air Drying

To explore the drying characteristics and the moisture diffusion mechanism in drying process of the Star anise, the hot-air experiment and low-field nuclear magnetic resonance (LF-NMR) of the Star anise were carried out and the quality of dryed Star anise were analyzed, where the experimental variables were drying temperature (50, 60 and 70 ℃) and pretreatment ( blanching ).The results showed that the drying process was basically in the falling rate period. The drying time was negatively correlated with the drying temperature of the hot air, and the blanching process could reduce the drying time.Three peaks were found in the fresh Star anise through low-field nuclear magnetic resonance.Through the drying process, it was found that 1~2 kinds of peaks could be separated from the water peak which was not easy to flow, and those were macromolecular organic matter. According to the area of each peak and the proportion of each component, most of the water removed from the Star anise in the drying process was non-flowing water, and there was a small change in the mass of the bound water, macromolecular organic matter and small molecule organic matter changed little. The pretreatment had little effects on the peak distribution of Star anise during the drying process, but the drying speed could be shortened. The quality of Star anise was showed that the dried Star anise was brighter in color, stronger in the rehydration rate, but greater in shrinkage rate after blanching. And the higher the hot air temperature was, the higher rehydration rate but higher shrinkage rate the dried Star anise had.