Investigation of hot air-assisted radio frequency heating as a simultaneous dry-blanching and pre-drying method for carrot cubes

Hot air-assisted radio frequency (HA-RF) heating was studied as a novel method for simultaneous dry-blanching and pre-drying of carrot cubes, and ultrasound-assisted osmotic dehydration (UOD) was also investigated as an improved conventional pre-drying method for comparison. After conventional hot water blanching, UOD was optimized by orthogonal experiment and after 30.0 min UOD treatment at optimal condition (10% sodium chloride, 40% sucrose and 1,4 solid-liquid ratio), moisture content of carrot cubes decreased to 58.5% (w.b.); and after 9.0-12.0 min HA-RF treatment, moisture content decreased to 60.9-71.9% (w.b.) and enzyme activity (peroxidase-POD) could be reduced to < 5% at the same time. UOD was better in lowering water activity and retaining redness of carrot cubes, while HA-RF treated samples had higher vitamin C content and better texture. Besides, HA-FIF pre-treatment had lower energy consumption (< 0.20 kW.h/kg) than that of hot water blanching plus UOD treatment (0.67 kWh/kg). This study indicated that HA-RF was an effective simultaneous dry blanching and pre-drying method for carrot cubes. Industrial relevance: This study proposed and investigated hot air-assisted radio frequency (HA-RF) heating as a new simultaneous dry-blanching and pre-drying method for carrots cubes. This technology may replace the conventional blanching and the following pre-dewatering or 1st stage drying process, since HA-RF pretreatment maintained good quality of carrot cubes and had lower energy consumption, and most importantly, this method can blanch and partially dehydrate samples at the same time without using water. Therefore, it holds great potential as the industrial pre-treatment method for drying of fruits and vegetables.