Tannins are generally considered to be water-soluble polyphenolic compounds with a molecular mass of 500-3,000 ku0 In addition to their phenolic properties, tannins can precipitate alkaloids, gelatin and proteins, etc. Tannins are found in the roots, stems, leaves, flowers and fruits of many plants and are associated with astringency before and after ripening. Tannins are found in the roots, stems, leaves, flowers and fruits of many plants, and are closely related to the astringent flavor of fruits before and after ripening. Tannins have also been found in the seeds of barley, wheat and many food legumes. The determination of tannin content provides information on the quality of fruits, vegetables and crops.
Principle
The basic principle of the determination of tannin content in sorghum grain is based on the fact that tannin contains aromatic hydroxyl groups that can reduce phosphorus bustard key acid, and in sodium carbonate medium, it can reduce the 6-valent bustard (key) of the color developer to 5-valent, showing calcium (key) dark blue, and the color depth is directly proportional to the content of tannin. In this experiment, the tannins in sorghum were extracted and reacted with phosphorus bustardic acid in sodium carbonate solution to produce a dark blue color and determine the content of tannins.
Operation method
Determination of tannin content in sorghum grain
Principle
The basic principle of the determination of tannin content in sorghum grain is based on the fact that tannin contains aromatic hydroxyl groups that can reduce phosphorus bustard key acid, and in sodium carbonate medium, it can reduce the 6-valent bustard (key) of the color developer to 5-valent, showing calcium (key) dark blue, and the color depth is directly proportional to the content of tannin. In this experiment, the tannins in sorghum were extracted and reacted with phosphorus bustardic acid in sodium carbonate solution to produce a dark blue color and determine the content of tannins.
Materials and Instruments
1. Material: Sorghum seeds. Move The basic procedure for the determination of tannin content in sorghum seed can be divided into the following steps: 1. Drawing of standard curve: Pipette 0, 1.0, 2.0, 4.0, 6.0, 8.0 mL of freshly prepared 0.1 mg - mL-1 tannic acid storage solution in 100 mL volumetric flasks, and then add 5 mL of F-D reagent and 10 mL of saturated Na2CO3 solution, evaporated water to 100 mL, and fully shaken. 30 min later, read the optical density value at 760 nm with a spectrophotometer. After 30 min, the optical density value was read at 760 nm with a spectrophotometer. The optical density value was read at 760 nm with a spectrophotometer, and the standard curve was plotted with the optical density value as the vertical coordinate and the amount of tannic acid as the horizontal coordinate. 2. Caveat 1. When sodium carbonate is used, centrifuge the colorimetric solution before colorimetry if it appears milky white and cloudy or precipitates. 2. If NaOH is used as the medium, the turbidity or precipitation should be eliminated. For more product details, please visit Aladdin Scientific website.
3. Apparatus: thermostatic water bath, thermostat, volumetric flasks, centrifuge, pipettes, beakers. Funnel, spectrophotometer.
2. reagents:
(1) F-D (Folin-Denis) reagent: 1 000 mL flask with 750 mL of steaming water, then add Na
2
WO
4
- 2 H
2
O 100 g, phosphonic acid 20 g and H
3
PO
4
(85%) 50 mL, tightly plugged with a rubber stopper, plug in a clean 50 ~ 100 cm long fine glass tube, glass tube inserted into the lower end of the solution, the flask on the adjustable furnace (plus asbestos mesh), and fixed on an iron frame, warm fire boiling reflux 2 h, cooled down and then diluted to 1,000 mL of distilled water.
(2) Saturated Na
2
CO
3
solution.
(3) 0.1 mg - mL・Tannic acid reserve solution: weigh 10 mg of tannic acid and dissolve it in water, then make it into 100 mL.
2. Sample extraction: Hand-select the whole grain sorghum samples, remove the glumes, broken grains and debris. Weigh 5 g of the sample into a 100 mL beaker, add 50 mL of water, and place the sample in an incubator at about 60°C overnight. The next day, the supernatant was filtered into a 250 mL volumetric flask, and then about 40 mL of distilled water at 80°C was added, and the sample was immersed in a water bath at 80°C for 20 min, then the filtrate was filtered into the 250 mL volumetric flask mentioned above, and the process was repeated for 3~5 times until the sample was extracted (checking method: the last filtrate no longer produces a greenish color or bluish color when it was mixed with dilute solution of FeCl3). Finally, the filtrate should be volume to 250 mL, shake well. 3.
3. Sample Determination: Take out part of the extract centrifuged, aspirate 1 mL ± clear solution, placed in a pre-set 70 mL of 70 mL of steaming water in a 100 mL volumetric flask, add 5 mL of F-D reagent and 10 mL of saturated Na2CO3 solution, steam pyruvic water volume to 100 mL, and fully shaken well. 30 min later. After 30 min, the optical density was read at 760 nm with a spectrophotometer. 4.
4. Calculation of the results:
Tannin content = ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ XI. %
where: A-amount of tannic acid found from the standard curve, mg;
W-sample weight, g.