To make the extraction buffer for the peroxidase enzyme, mix equal volumes of 0.1 M sodium phosphate monobasic and 0.1 molar sodium phosphate dibasic solutions to achieve a final volume of 500 mL.
Test the resulting solution using a pH meter. The mixture should be between a pH of 6.8 and 7.2.
To extract the turnip peroxidase, use a knife to remove the outer layer of a turnip and then cut the turnip into approximately two cm cubes.
Place 30 g of turnip cubes into a blender with 300 mL extraction buffer, and blend the turnip cubes at high speed three times for about 15 s each time.
Filter the homogenized mixture through three layers of cheesecloth, then strain the resulting solution through one coffee filter.
Store the filtrate in a 500 mL bottle, and immediately place the bottle in the refrigerator.
Next, to make the enzyme substrate solutions, first add 15 mL 3% H2O2 to 435 mL distilled water to dilute the H2O2 to a 0.1% concentration.
To prepare the color-changing reactant, dissolve 0.2 mL concentrated guaiacol in 100 mL of isopropyl rubbing alcohol, and store this guaiacol solution in the refrigerator.
Then, to make solutions for the different pH conditions, add 100 mL distilled water to six 250 mL beakers, and place the buffer capsule contents with pH of 3, 4, 5, 6, 7, and 8 into separate beakers.