CB21 - Polyphenol Oxidase as an Indicator of Antioxidant Capacity in Black and Green Teas
SCURS Disciplines
Biology
Document Type
General Poster
Invited Presentation Choice
Not Applicable
Abstract
Green tea is rich in polyphenolic enzymes that contribute to its antioxidant properties. Polyphenol oxidase (PPO) catalyzes the oxidation of certain phenolic substrates but may alter under certain preparation conditions. Our study is multifaceted; the first goal in our study aims to quantify the effectiveness of PPO using a caffeic acid assay and a 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical assay to see how alterations in preparation will change the potency of the enzyme in green tea. Our second goal in this study was designed to observe whether a specific brand of green or black tea has a higher antioxidant capacity. Since green tea has freer phenolic -OH groups per molecule than black tea, then green tea should have a higher antioxidant capacity. The DPPH assay is widely used to evaluate free radical scavenging ability because it is able to provide a rapid measurement of electron-donating capacity. A high absorbance meant low antioxidant activity, and a low absorbance meant high antioxidant activity. The green tea had an antioxidant capacity of 71.2% and the black tea had an antioxidant capacity of 72.0% varying less than 5% with each other contrary to expected results according to literature.
Therefore, two assays were selected to measure PPO activity in brewed tea samples. Kinetics of PPO activity in our experimentation on red delicious apples had a resulting Vmax of 5.0*105 mM/s and a Km value of 1.0*1012 mM. However, since the caffeic acid assay system we developed relies on Caffeic acid o-quinone precipitate formation rather than colorimetric absorbance, we sought to develop a protocol for measurements with L-DOPA as the substrate for PPO for brewed tea. The enzymatic reaction of L-DOPA with PPO produces Dopachrome, which is relatively stable at room temperature and produces a significant color change to yellow orange. Use of L-DOPA substrate in measuring PPO activity resulted in comparable results to caffeic acid assay.
The results of these assays demonstrate that antioxidant capacity parallels PPO activity in both green and black tea. Future studies can be done to understand the molecular mechanisms that allow the Lipton tea brand to have similar antioxidant capacities for their green and black teas. Furthermore, even though multiple foods such as apples contain significant antioxidant levels, tea’s global routine consumption makes it a particularly important contributor to overall antioxidant intake.
Keywords
DDPH, polyphenol oxidase, PPO, green tea, black tea
Start Date
10-4-2026 9:30 AM
Location
University Readiness Center Greatroom
End Date
10-4-2026 11:30 AM
CB21 - Polyphenol Oxidase as an Indicator of Antioxidant Capacity in Black and Green Teas
University Readiness Center Greatroom
Green tea is rich in polyphenolic enzymes that contribute to its antioxidant properties. Polyphenol oxidase (PPO) catalyzes the oxidation of certain phenolic substrates but may alter under certain preparation conditions. Our study is multifaceted; the first goal in our study aims to quantify the effectiveness of PPO using a caffeic acid assay and a 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical assay to see how alterations in preparation will change the potency of the enzyme in green tea. Our second goal in this study was designed to observe whether a specific brand of green or black tea has a higher antioxidant capacity. Since green tea has freer phenolic -OH groups per molecule than black tea, then green tea should have a higher antioxidant capacity. The DPPH assay is widely used to evaluate free radical scavenging ability because it is able to provide a rapid measurement of electron-donating capacity. A high absorbance meant low antioxidant activity, and a low absorbance meant high antioxidant activity. The green tea had an antioxidant capacity of 71.2% and the black tea had an antioxidant capacity of 72.0% varying less than 5% with each other contrary to expected results according to literature.
Therefore, two assays were selected to measure PPO activity in brewed tea samples. Kinetics of PPO activity in our experimentation on red delicious apples had a resulting Vmax of 5.0*105 mM/s and a Km value of 1.0*1012 mM. However, since the caffeic acid assay system we developed relies on Caffeic acid o-quinone precipitate formation rather than colorimetric absorbance, we sought to develop a protocol for measurements with L-DOPA as the substrate for PPO for brewed tea. The enzymatic reaction of L-DOPA with PPO produces Dopachrome, which is relatively stable at room temperature and produces a significant color change to yellow orange. Use of L-DOPA substrate in measuring PPO activity resulted in comparable results to caffeic acid assay.
The results of these assays demonstrate that antioxidant capacity parallels PPO activity in both green and black tea. Future studies can be done to understand the molecular mechanisms that allow the Lipton tea brand to have similar antioxidant capacities for their green and black teas. Furthermore, even though multiple foods such as apples contain significant antioxidant levels, tea’s global routine consumption makes it a particularly important contributor to overall antioxidant intake.