The effect of ohmic blanching on the chlorophyll content, color characteristics, and polyphenol oxidase (PPO) activity of Mekai leaves (Pycnarrhena tumefacta miers)

Abstract

Mekai leaves (Pycnarrhena tumefacta miers) are traditionally used as natural flavor enhancers; however, conventional drying often causes chlorophyll degradation and color loss. This study evaluated the effect of ohmic blanching on the chlorophyll content, color characteristics, and polyphenol oxidase (PPO) activity of Mekai leaves prior to drying. Ohmic blanching was applied at 80, 85, and 90 °C for 5, 10, and 15 min using a laboratory-scale static ohmic heater. The results showed that ohmic blanching significantly influenced pigment stability and visual appearance. Chlorophyll degradation increased with higher temperatures and longer heating durations, with chlorophyll b being more heat-sensitive than chlorophyll a. Among the tested conditions, treatment at 85 °C for 10 min resulted in the highest retention of green color and chlorophyll content and showed a relatively high Specific Performance Coefficient (SPC = 0.893), indicating efficient energy utilization. This condition also produced lower ΔE and higher green intensity (a* value), accompanied by a substantial reduction in PPO activity. These findings suggest that ohmic blanching may serve as a promising pretreatment to maintain the visual and functional quality of Mekai leaves prior to drying.

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