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.

Assessment of microwave drying for rapid and convenient analysis of medicinal plants for quality assurance

“…Lin et al 55 reported that the release of active oxidative enzymes (PPO and peroxidase) could cause enzymatic degradation and therefore reduce the number of extractable phenolics when leaf tissues are damaged. As PPO enzymes are involved in the production of quinones from monophenols and diphenols, it is logical to expect that high PPO activity would degrade more phenolics in the plant leaf samples 53 . Moreover, most plant tissues contain isoenzymes of PPOs with different substrate affinity and thermal stability.…”

“…As PPO enzymes are involved in the production of quinones from monophenols and diphenols, it is logical to expect that high PPO activity would degrade more phenolics in the plant leaf samples. 53 Moreover, most plant tissues contain isoenzymes of PPOs with different substrate affinity and thermal stability. This is probably the reason why in different drying conditions, specific polyphenols may be present or absent.…”

Feasibility of microwave drying for analysis and processing of medicinal plants

“…For example, EGF showed more PPO activity in freeze dried samples but ENF showed more activity in 50ºC dried sample. According to Loh et al [35] as polyphenol oxidase activity increased, the percentage loss in TPC also increased; however, there was no obvious trend observed for the peroxidase enzyme. Reports also stated that enzymatic activities generally decreases with decreasing water activity [36].…”

“…Lin et al [37] reported that the release of active oxidative enzymes (PPO and POD) could cause enzymatic degradation and therefore reduce the number of extractable phenolics when leaf tissues were damaged. As PPO enzymes are involved in the production of quinones from monophenols and diphenols, it is logical to expect that high PPO activity would degrade more phenolics in the plant leaf samples [35]. Moreover most plant tissues contain isoenzymes of PPOs with different substrate a nity and thermal stablity.…”

Screening, identification, and mechanism analysis of starch-degrading bacteria during curing process in tobacco leaf

“…Enzyme activity were crucial factors that influence the degradation of starch of tobacco leaf during curing process Frontiers in Bioengineering and Biotechnology frontiersin.org (Lacerda et al, 2018;Loh et al, 2018). Consequently, the activities of enzymes related to starch degradation (SOD, POD, PPO, α-amylase, β-amylase, total amylase, SBE) at temperatures of 38 °C, 40 °C, 42 °C, 44 °C, and 46 °C were measured during the curing process (Figures 2A, B, D-H).…”