Hydrolysis and extraction of carbohydrates in the sample: accurately weigh 2 g of ground fresh vegetables into a 25 mL test tube, rinse the test tube wall with a little water, add 7.5 mL of hydrochloric acid, and then bring the volume to 15 mL with water and mix well in a boiling water bath After heating for 45min, check the degree of starch hydrolysis with potassium iodide-iodine solution. If the hydrolysis is complete, it will not appear blue. After cooling, add 1 drop to 2 drops of phenolphthalein indicator, and neutralize with sodium hydroxide solution until the solution is reddish , Filter and dilute to 25mL for use. Draw a standard curve: accurately weigh 100 mg of glucose in 100 mL of water as a standard solution, take 8 large test tubes and add 0.1, 0.2, 0.4, 0.8, 1.2, 1.6, 2.0 mL of 1.0 me/mL glucose standard solution in a 25 mL test tube , Add water to 5mL, then add 1.5mLDNS reagent to heat 5rain in boiling water bath. Immediately cool with tap water, dilute to 25mL and mix well. At a wavelength of 540nm, use the reagent blank as the reference solution to measure the absorbance A of each solution. Draw a standard curve. Determination of sugar content in the sample: each vegetable shares a blank control, take 1mL of the test solution, then add water to 5mL, add 1.5mL DNS reagent, heat 5rain in a boiling water bath, cool it with tap water and dilute to 25mL. Evenly, the absorbance A value is measured at a wavelength of 540 nm, and the corresponding carbohydrate content can be found on the standard curve with the measured A value.
Take 10g of the sample, grind it into a slurry with a mortar, add metaphosphoric acid-acetic acid solution to 10mL, stir it for 3min and then filter, take the filtrate as the sample solution. Accurately take a 20mL volume of sample solution in a 100mL iodine flask and add 10mL of 30% KI solution. Add a few more drops of starch indicator solution. Then titrate with 0.01 mol/L copper sulfate solution. Till blue, record the titration. Do another blank test. In the calculation, subtract the titration of the blank test from the titration of the sample to obtain V. L-ascorbic acid content=V×C. In the formula: V=0.01 mol/L standard copper sulfate solution volume, mL; C=0.88, that is 1mL 0.01 mol/L standard copper sulfate solution is equivalent to 0.88 mg ascorbic acid.
Soluble protein determination
Precisely weigh 100 mg of casein in 100 mL of water as a standard solution. Take a series of test tubes, add 0, 0.4, 0.8, 1.2, 1.6, 2.0 mL of the prepared standard casein solution, make up to 2 mL with water, then add 4 mL of biuret reagent at room temperature (15 °C to 25 ℃) Place for 30min, measure at 550nm wavelength, and use the reagent blank as the reference solution to measure the absorbance A of each solution. Draw a standard curve. Sample determination: First, take a certain weight of vegetables and crush them with a tissue masher. Take 2 mL of vegetable liquid, then add 4 mL of biuret reagent, shake for 10 min, let stand at room temperature for 30 min, transfer the supernatant to a centrifuge tube. Centrifuge at 4000r/min for 5min, and take the supernatant 15-61. Measure the absorbance A value at 550nm wavelength, and use the measured A value to check the corresponding soluble protein content on the standard curve.