Tri-frequency ultrasound as pretreatment to infrared drying of carrots: impact on enzyme inactivation, color changes, nutrition quality parameters and microstructures

摘要

The effects of tri-frequency ultrasound as pretreatment on the peroxidase (POD) inactivation and infrared drying attributes of carrots were studied in the temperature range of 60-80 degrees C. Thermosonication (TS) treatment reduced 65.21, 73.33 and 81.43% POD activity after 5 min for the temperatures at 60, 70 and 80 degrees C, respectively, which were all higher than hot water (HW) blanching treated samples. The first-order kinetics fitted well for the POD inactivation curves. Similar retention ranges of vitamin C (VC) were observed after TS (88.41-82.51%) and HW (91.91-88.75%) treatments at the studied range of temperatures. Compared to HW treated samples, drying times of thermosonicated carrot slices were shortened by 13.6, 15 and 15.8% for blanching temperatures at 60, 70 and 80 degrees C, respectively. The aid of ultrasound showed a positive effect on the rehydration ration (RR) of samples. Sonicated dried samples exhibited higher hardness compared with thermal dried samples. No significant variation (p > 0.05) in the total color difference (Delta E) was attained for dried carrot slices pretreated by TS and HW processes.