LAUSR

Gingko biloba (GB) seeds were dried by hot air under drying temperature of 60, 70, 80, and 90 °C. The crust formation of GB seeds during drying process was monitored by stereomicroscopy. A line dividing the illuminated and dark part was observed from the stereoscopic image, of which the dark part was the crust layer. The degree of crust under drying process was represented by crust ratio rather than the absolute thickness of the crust layer due to the shrinkage phenomenon during drying. The crust ratio increased with the drying time in all cases. It was also found that drying temperatures had significant effects on the crust formation. Zero-order model was successfully applied to describe the crust ratio changes. Activation energy for crust formation was calculated for 53.91 kJ/mol by the Arrhenius equation. The microstructure observed by scanning electron microscope (SEM) indicates that the crust layer had an obvious dense structure compared with the non-crust part, which well proved the reasonableness of using stereomicroscope to evaluate the crust degree. The combination of the two microscopy techniques (stereomicroscopy and SEM) provides a feasible method for observation and evaluation of the crust formation in the drying process.