Study on the effects of radio frequency blanching on polyphenol oxidase activity, physicochemical properties, and microstructure of iron yam

The effects of radio frequency (RF) and hot water blanching on polyphenol oxidase (PPO) activity, physicochemical properties, and microstructure of iron yams were investigated. The heating rate of RF was the largest, and the heating uniformity was the best at the electrode gap of 160 mm and the material height of 90 mm. The residual activity of PPO was significantly reduced from 49.95% to 4.21%, whereas the RF heating temperature (65-85°C) increased (p < 0.05). The color and texture of yams treated with RF blanching were better preserved compared with those of hot water blanching at a similar degree of enzyme inactivation. The microstructure showed that these changes in physicochemical properties were caused by cellular damage. The surface cells of yams were more severely damaged than the center cells after hot water blanching at 95°C for 3 min. Moreover, the surface cells after hot water blanching also showed more damage than the cells after RF blanching. Thus, RF blanching is a technique with development potential in the food industry.