Steam-assisted Radio Frequency Blanching to Improve Heating Uniformity and Quality Characteristics of Stem Lettuce Cuboids

Non-uniform heating of RF energy is the main obstacle for its large-scale application in blanching. In this study, we proposed a new blanching method: steam (ST)-assisted radio frequency (RF) blanching of fresh-cut stem lettuce cuboids. The relative peroxidase (POD) activity, heating uniformity, and physicochemical properties of samples treated by steam-assisted RF blanching at different conditions (RF-50 °C + ST-2.5 min, RF-65 °C + ST-2 min, and RF-80 °C + ST-1 min) were evaluated in comparison with single RF heating and steam blanching. Both the temperature distribution images and the heating uniformity index indicated that steam-assisted RF blanching overcame the defect of local overheating of single blanching mode and achieved more uniform temperature distribution. Besides steam-assisted RF, blanched reduced the thermal damage to cells, which can be demonstrated by lower relative electrolyte leakage rate, thereby maintained better texture, color, and higher vitamin C retention at the same relative POD activity of 5%. Among the three steam-assisted RF blanching treatments, RF-80 °C + ST-1 min achieved optimum heating uniformity and quality of samples. This study suggested that steam-assisted RF blanching can be used as a potential blanching method to improve inactivation efficiency of enzyme and quality of fruits and vegetables.