Hot air drying combined vacuum-filling nitrogen drying of apple slices: Drying characteristics and nutrients

In this paper, hot air drying (HAD) was applied when moisture content of apple slices range from 50% to 86%, and then vacuum filling nitrogen drying (VFND) was used till moisture content reaching 7%. Results showed that, the drying rate of apple slice during VFND period increased with temperature increment and decreased with increment of slice thickness; compared to freezing dried samples, samples dried in this research were owned lower Vc and higher flavonoid; when HAD (70 degrees C, 3.0 m/s)+VFND(relative pressure 0.08 MPa, 50 degrees C) and thickness of 6.0 mm, nutrients reached better levels: retentions of Vc, total phenolics and flavonoid were 1.63 mg/100 g, 4.07 mg/100 g and 2.10 mg/100 g, respectively.