Combined radio frequency and steam blanching of iron yam (Dioscorea opposita Thunb.): Effect on polyphenol oxidase inactivation, heating uniformity, physicochemical properties, and microstructure

Iron yam ( Dioscorea opposita Thunb.) is widely valued as a medicinal and food resource but is highly susceptible to enzymatic browning due to its abundant polyphenol oxidase (PPO), which severely degrades its processing quality. To address these issues, this study developed a novel simultaneous blanching system and systematically compared the effects of radio frequency blanching (RF), 100 °C saturated steam blanching (SS), 110 °C superheated steam blanching (SSB), and RF combined with steam blanching (RF+SS and RF+SSB) on PPO inactivation, heating uniformity, physicochemical properties, and microstructure of iron yams. The heating uniformity indices ( λ ) values of RF+SS (0.058–0.068) and RF+SSB (0.055–0.062) were significantly lower than other treatments ( P <0.05), indicating more uniform temperature distribution. Under the same PPO inactivation conditions, the RF+SSB group had shorter processing time (45 s), better color (Δ E = 3.26±0.62) texture, Vitamin C (82.50±1.64 %) retention of yam, and a lower relative electrolyte leakage (REL) (63.1%). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations further revealed that RF+SSB caused minimal cell disruption. RF combined with steam blanching is an innovative and promising blanching method to enhance the enzyme inactivation efficiency and quality of fruits and vegetables, which is important for fruit and vegetable processing.