Microwave Drying of Pitaya (Hylocereus) Peel and the Effects Compared with Hot-Air and Freeze-drying

摘要

Microwave drying (MD) of pitaya peel was performed at 75, 225, 375, 525, and 750 W. The drying effects on the effective moisture diffusivity (De), total polyphenol content (TPC), betalain content, DPPH scavenging ability, and rehydration abilities ofpitaya peel were examined. The data were compared with hot-air drying (HD) at 100°C for 4 h and freeze-drying (FD) for 24 h. The results showed that the MD kinetics ofpitaya peel fit Fick 's law and theArrhenius equation with an activation energy (Ea) of34.08 Wg'1. The De values of MD, which rangedfrom 2.35E-07 m2 s'1 (at 75 W) to 5.56E-06 m2 s'1 (at 750 W), indicated that the effectiveness of MD was appreciably higher than that of HD (2.44E-08 m2 s~') and FD (4.43E-09 m2 s'1). Although MD resulted indecreased betacyanin (9.31 mg L'1 extract) and betaxanthin (6.58 mg L'1 extract) contents, the DPPH inhibition of pitaya peel remained at 7 5% due to an increase in TPC (115 mg GAEper 100 FW). MD of pitaya peel can also provide higher rehydration abilitythan HD and was comparable to FD. This study concludes that MD of pitaya peel was highly effective while maintaining high levels of TPC and DPPH inhibition.