- In this small blog post, we will see how to determine Tannin Content in Food
- Tannins are a class of polyphenolic compounds that are found in many plants. They are responsible for the astringent taste of some foods, such as tea, red wine, and walnuts. Tannins can also have a number of health benefits, such as antioxidant and anti-inflammatory activity.
- There are two main types of tannins:
- Condensed tannins: These tannins are made up of multiple units of flavonoid molecules that are linked together by carbon-carbon bonds.
- Hydrolysable tannins: These tannins are made up of flavonoid molecules that are linked together by ester bonds.
- The tannin content of a food or beverage can vary depending on the type of plant material, the processing methods used, and the storage conditions. For example, tea leaves contain high levels of condensed tannins, while red wine contains high levels of hydrolysable tannins.
- Tannins have a number of health benefits, including:
- Antioxidant activity: Tannins can help to protect cells from damage caused by free radicals.
- Anti-inflammatory activity: Tannins can help to reduce inflammation.
- Antimicrobial activity: Tannins can help to kill bacteria and viruses.
- Anticancer activity: Tannins have been shown to inhibit the growth of cancer cells.
- However, tannins can also have some negative effects, such as:
- Irritating to the digestive system: Tannins can cause a dry mouth, nausea, and vomiting.
- Interfering with the absorption of nutrients: Tannins can bind to nutrients in the digestive tract and prevent them from being absorbed.
- Binding to proteins: Tannins can bind to proteins and make them less digestible.
Overall, tannins are a group of compounds with a wide range of potential health benefits and risks. The specific effects of tannins on health will depend on the type of tannin, the amount consumed, and the individual’s health status.
Here are some examples of foods that contain tannins:
- Tea: Black tea, green tea, and white tea all contain high levels of tannins.
- Red wine: Red wine contains high levels of hydrolysable tannins.
- Walnuts: Walnuts contain high levels of condensed tannins.
- Oak bark: Oak bark is used to make tannin extract, which is used in a variety of applications, including tanning leather and making wine.
- Coffee: Coffee beans contain some tannins, but the amount of tannins in coffee can vary depending on the brewing method.
Methods for determining tannin content:
There are a number of methods for determining the tannin content of food. Some of the most common methods include:
- Folin-Ciocalteu method: This method is based on the ability of tannins to precipitate proteins. The sample is reacted with a solution of Folin-Ciocalteu reagent, which produces a blue-purple color. The intensity of the color is then measured and used to calculate the tannin content.
- Vanillin-HCl method: This method is based on the ability of tannins to react with vanillin in the presence of hydrochloric acid to produce a pink color. The intensity of the color is then measured and used to calculate the tannin content. (We will discuss this method in detail:))
- Bradford method: This method is based on the ability of tannins to bind to bovine serum albumin (BSA). The sample is reacted with a solution of BSA, and the absorbance of the resulting solution is measured at a specific wavelength. The absorbance is then used to calculate the tannin content.
- Spectrophotometric method: This method is based on the ability of tannins to absorb light in the visible region of the spectrum. The sample is diluted in a buffer solution, and the resulting solution’s absorbance is measured at a specific wavelength. The absorbance is then used to calculate the tannin content.
The choice of method will depend on the specific application. The Folin-Ciocalteu method is a relatively simple and inexpensive method, but it is not as specific for tannins as some of the other methods. The vanillin-HCl method is more specific for tannins, but it is also more time-consuming and requires more specialized equipment. The Bradford method is a very sensitive method that can be used to measure very low levels of tannins, but it is also more expensive than some of the other methods. The spectrophotometric method is a very versatile method that can be used to measure a wide range of compounds, including tannins.
Step 1: Take 1g of your food sample in a centrifuge tube and add 10ml acidifying methanol in the ratio of 1:100 (i.e. Add 0.1mL HCl in 10ml methanol)
Step 2: Incubate for 15hrs at room temperature
Step 3: Centrifuge at 7000rom for 15 minutes
Determine Tannin Content in Food
Step 4: Take 1ml from this supernatant and add 5ml Vanillin: HCL reagent
How to prepare Vanillin: HCL reagent
Solution A- Add 4g Vanillin in 100ml methanol
Solution B- Prepare 100ml of acidifying methanol in a ratio of 1:12.5
Mix solutions A and B.
Step 5: Record the absorbance at 500nm using UV spectrophotometer.
The standard curve is prepared by using Tanninc acid and expressed as mg TA/ 100g of dry matter
How to prepare standard for the determination of Tannin content ?
Mix 1 g Tannic Acid in 10mL of acidified methanol
Above on mixing will be the stock solution
Below is the complete step-by-step procedure taken for the tannin content determination in the control food sample and Samples 1 to 6.
Also, Blanks 1 and 2 are the two Blanks taken for calibration.
See the figure below to understand clearly
Plot curve between Absorbance on y axis and standard concentration on x axis.
Then interpolate the values of concentration of tannin in the food sample from the equation of straight line obtained through the plot, and finally express in mg/ml of tannic acid.
The determination of tannin content in food is an important tool for assessing the nutritional value, safety, and quality of food. There are several methods available for determining tannin content, and the choice of method will depend on the specific application.