Blog #2

I have made significant progress in my research since the posting of my first blog. My research time has been split between literary research and research in the laboratory. In regards to literary research, I have been trying to find more assays than the two I have chosen that would produce useful results. Aside from the DPPH and Folin-Ciocalteu assays, I have been studying the 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid or ABTS assay. The ABTS assay allows for antioxidant activity to be measured and so it will be an additional assay to test antioxidant activity of the tea samples. Dr. Mojica and I are in the process of finalizing a protocol for this assay as well as ordering the necessary chemical reagents needed.

In the laboratory, bags from the tea samples were dipped into 200 mL of freshly boiled water for ten minutes. Once the tea was made, the bags were removed and the tea infusions were allowed to completely cool. The infusions need to be cool or room temperature in order to ensure that the results produced by the UV-Vis are as accurate as possible. In the Folin – Ciocalteu assay, 0.1 mL of the tea infusion in gallic acid solution was mixed with 0.1 mL of the Folin – Ciocalteu reagent and 0.9 mL of water. The mixture stood for five minutes and then was added to 1.0 mL of sodium carbonate and 0.4 mL of water. The absorbance reading at 765 nm was obtained after initial mixture, thirty minutes, and then sixty minutes. In the DPPH assay, DPPH (2,2-diphenyl-1-picrylhydrazyl) solution in 2.4 mL of methanol was mixed with 0.1 mL of the tea infusion. The absorbance reading at 539 nm was obtained after initial mixture, thirty minutes, and then sixty minutes.

My next step is to enter the results obtained from the UV-Vis into an Excel spreadsheet and create graphs using Excel and the program IGOR. Mixing and reading all twelve of my samples has been very time-consuming. Since half of the samples are green tea and the other half are black tea, I have been trying to mix and read all green teas at once and all black teas at once. Labeling the samples has helped tremendously because samples are the same color when made and it avoids contamination or incorrect readings. So far the readings are making sense and there is a direct relationship between antioxidant activity and phenolic content. My goal when I enter the data into a processing program is that the relationship will become much clearer. I will mix and read the samples again so that I can confirm my original research findings. Since the semester is winding down and finals are approaching, it has become difficult to dedicate as much time in the laboratory as I would like but Dr. Mojica and I will meet many times over the winter break to continue testing and reading my samples. I have placed my samples in the fridge and the next time I read them, I would like to see if there is any change in the results since they have been chilled as opposed to just being made and at room temperature. This will allow me to look at the data in a new light and see if temperature affects antioxidant activity and phenolic content.

Phenol Content and Antioxidant Activities of Different Commercial Tea Samples

Tea is the most consumed beverage in the world next to water. The total amount of tea produced and consumed in the world can be broken into 78% black, 20% green and < 2% is oolong tea. Black tea is consumed primarily in Western countries and in some Asian countries, whereas green tea is consumed primarily in China, Japan, India, and a few countries in North Africa and the Middle East. Oolong tea production and consumption are confined to southeastern China and Taiwan. There are three major classes of plant chemicals: terpenoids, phenolic metabolites, and alkaloids. Among these three groups, phenolic compounds are the most important for dietary applications and the most extensively researched.

Phenolic compounds include phenolic acids (hydroxybenzoic and hydroxycinnamic acids), polyphenols (hydrolyzable and condensed tannins), and flavonoids. These compounds protect plants, fruits, vegetables, and the humans that consume them from oxidative damage. Phenols are one of the main secondary metabolites present in plants. They are found in both edible and non – edible plants and have been reported to have many biological effects. Phenolic compounds are an extensively studied group of compounds that come from natural sources. Flavonoids are a type of phytochemical that possess a number of biological activities. They are the most common group of polyphenolic compounds that are found everywhere in plants. Flavonoids and other plant phenolics are common in leaves, flowering tissue and woody parts such as stem and bark (Gupta et al. 2012).

Antioxidants protect us from dangerous substances called free radicals that can lead to many chronic diseases. Antioxidants include secondary metabolites, enzymes and high/low molecular weight proteins that act against these free radicals. Phenolics from plants act as a source of natural antioxidants and have many functions including being reducing agents, metal chelators and quenchers of oxygen singlets (Shalini et al. 2010).

The purpose of this research project is to determine the phenol content and antioxidant properties of the water extracts of 12 commercially available teas. The results will then be evaluated and compared with one another. The total phenolic content will be determined by the Folin-Ciocalteu method with gallic acid used as the standard. The antioxidant properties will be evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay system. This project aims to determine which tea samples have the highest phenol content and antioxidant activity as well as further our understanding of these two properties of tea. To determine both phenolic content and antioxidant activity, UV – Vis spectroscopy will be used and the results will be tabulated in an Excel spreadsheet to observe any similarities or differences between the samples. This project is important to explore because tea is consumed by almost everyone worldwide. This research will be able to provide the public with more insight into how beneficial tea is to the human body.