Effect of Ultrasound Pretreatment on the Retention of Loquat Phenolics and Antioxidants during Tray and Freeze-Drying

In this study, the effect of ultrasound (US) pretreatment (600W for 30 min) prior to tray drying (TD) (46±1°C at 1.10 m/s) and freeze drying (FD) (-58°C at 0.001 mbar) on the quality characteristics of loquat cubes was investigated. US pretreatment in TD demonstrated a significant decrease in drying time (19.67%) and an increase in drying rates (22.23%, p<0.05). With US pretreatment, the effective moisture diffusivity increased from 7.83x10^-9 to 8.92x10^-9 m²/s in TD. The highest rehydration capacity (4.47±0.23 g/g) was found in FD samples with US. In comparison to TD and control samples, FD samples had higher phenolic contents. US pretreatment significantly reduced phenolic contents from 1551.19±142.12 to 1197.03±80.51 mg GAE/100g and from 770.12±125.93 to 374.78±71.95 mg GAE/100g for FD and TD, respectively (p<0.05). The antioxidant capacity of loquat cubes significantly decreased with TD compared to FD (p<0.05). Results indicated that FD is a viable option for drying loquat cubes with a low moisture content, high rehydration capacity, and enhanced phenolic content and antioxidant activity.