Hawthorn Drying: An Exploration of Ultrasound Treatment and Microwave–Hot Air Drying

Abstract

Drying is one of the methods used for preserving fruits and vegetables. However, due to the lengthy process and elevated temperature of convective drying, other pretreatment and drying methods are studied to shorten the drying time and obtain high-quality products. This study aimed to examine the effect of ultrasonic (US) pretreatment and microwave–hot air drying (MW–HA) on the drying time, specific energy (SEC), qualitative properties (e.g., color, shrinkage, and rehydration ratio), and bioactive compound properties (e.g., antioxidant activity, phenolic, and flavonoid contents) of hawthorn fruit. Experiments were performed using ultrasound pretreatment and a microwave dryer (microwave power: 180, 360, and 540 W) at air temperatures of 40, 55, and 70 °C. Drying of hawthorn lasts from 35 min for the ultrasound-treated sample (dried at 540 W and 70 °C) to 180 min (dried at 180 W and 40 °C without US treatment). The lowest amount of SEC (24.11 MJ/kg) was obtained using the US–MW–HA air drying method (dried at 540 W and 70 °C). The lowest values in total color change (13.37) and shrinkage (22.47%) were recorded for the sample dried with a MW power of 360 W and air temperature at 55 °C with US pretreatment prior to drying. Generally, the use of US and MW–HA air drying reduces the antioxidant activity (AC), total phenolic content (TPC), and total flavonoid content (TFC) during processing compared to fresh samples. The highest values for AA (28.01%), TPC (69.44 mg GAE/g d.m.), and TFC (64.38 mg QE/g) obtained at 360 W and 55 °C with US pretreatment for hawthorn fruit dried.