Drying characteristics and modeling of apple slices during microwave intermittent drying

摘要

Drying characteristics and quality of apple slices were studied using microwave intermittent drying at different microwave power density (2.2, 3.5, 4.8, and 6.1 W/g), sample thickness (3, 5, 7, and 9 mm) and heating time in each cycle (4, 5, 6, and 7 s). Results showed that the approximate constant rate drying periods and falling rate drying periods were found in all the curves. The drying time decreased with increasing microwave power density and heating time in each cycle, while increased significantly with the growth of sample thickness. Weibull distribution model could fit the drying curves well in all conditions (R-2 > 0.99) with the scale parameter values changed from 45.88 to 206.08 min and the shape parameters values varied from 1.514 to 1.69. The moisture effective diffusivity calculated by Weibull model ranged from 0.3217 x 10(-9) to 1.435 x 10(-9) m(2)center dot s(-1). The flavor, texture and overall acceptability values displayed a decreasing tendency with the increase of microwave power density, while increased with the growth of thickness. And the shrinkage rates of apple slices showed a decline tendency with the increase of above parameters. Practical applications Apple is a kind of popular and important fruits with high nutrient content, and it has been widely planted in China. Due to its high moisture content, fresh apples will subject to various deteriorative reactions during storage and thus lead to serious post-harvest losses. Microwave drying technology has been widely used in dehydration of agricultural products in China because of the significant heating efficiency. However, the continuous microwave heating may easily cause the overheating of raw materials and undesirable changes in quality. Microwave intermittent drying (MID) was proposed on the basis of conventional microwave drying and regarded as an efficient processing method by solving the above issues. Currently this technology has been successfully applied to ginkgo fruits, yam and banana slices. Analyzing the effects of drying parameters on MID kinetics and quality of apple slices will have important significance for optimizing the processing efficiency and consumer acceptability of dried products.