Relationship between polyphenol oxidase activity and phenolics degradation on ambient air-drying of herbal plants

Abstract

Beneficial properties of herbal tea leaves can be affected by oxidase enzymes activity on harvesting, as these enzymes utilize phenolics as the main substrate. The purpose of this study was to investigate whether there is any correlation between the oxidase enzymes activity and the degree of phenolic degradation. Eight herbal tea leaves underwent ambient air-drying process and their total phenolic content change as well as polyphenol oxidase and peroxidase enzyme activity change for each fresh leaf were determined after ambient air-drying. Results showed that except for two plants, polyphenol oxidase activity had a positive linear correlation with total phenolic degradation (y = 1.929x + 21.082; R2 = 0.8909), but peroxidase activity showed no such relationship. Plants with rosmarinic acid as their main phenolics, showed a much better correlation. Practical applications The process of preserving herbal tea leaves for their bioactivities by drying is crucial for the purpose of commercialization. Herbal industries have been using, among others, air-drying method as a means of preservation because of its cost effectiveness. However, the presence of oxidase enzymes may lead to degradation of beneficial compounds. In our study, by identifying the correlation between oxidase enzyme activity for both polyphenol oxidase and peroxidase with that of total phenolic degradation, we are able to understand the actual effect of oxidase enzymes on phenolics degradation. Hence, through the correlation and solely based on its oxidase enzyme activity, mainly polyphenol oxidase, we could determine whether air-drying will be suitable for a particular herbal tea leaf. This will result in a much faster and efficient decision in choosing a preserving method for the herbal tea leaf.