Determination of edible corn starch content

First method enzymatic hydrolysis

First, the purpose and requirements:

1. Defining and mastering the principle and determination method of starch content in various foods.

2. Master the method for determining starch by enzymatic hydrolysis and acid hydrolysis.

Second, the principle

After the sample is removed from fat and soluble sugar, the starch is hydrolyzed to disaccharide by amylase, and then the disaccharide is hydrolyzed to monosaccharide with hydrochloric acid, and finally determined by reducing sugar and converted into starch.

Third, the reagent:

1. 0.5% amylase solution: Weigh 0.5g of amylase, add 100ml of water to dissolve, a few drops of toluene or chloroform to prevent mildew and store in the refrigerator.

2. Iodine solution: Weigh 3.6 g of potassium iodide dissolved in 20 ml of water, add 1.3 g of iodine, dissolve and dilute to 100 ml with water.

3, ether

4, 85% ethanol

5, 6N hydrochloric acid: Measure 50 ml of hydrochloric acid and dilute to 100 ml with water.

6. Methyl red indicator solution: 0.1% ethanol solution.

7, 20% sodium hydroxide solution.

8. Basic copper tartrate solution: Weigh 34.639 g of copper sulfate (CuS04·5H2O). Add appropriate amount of water to dissolve, add 0.5 ml of sulfuric acid, dilute to 500 ml with water, and filter with refined asbestos.

9. Basic copper tartrate solution: Weigh 173 grams of sodium potassium tartrate and 50 grams of sodium hydroxide, add appropriate amount of water to dissolve, and dilute to 500 ml, filter with refined asbestos, and store in a rubber stopper glass bottle.

10. 0.1000 N potassium permanganate standard solution.

11. Ferric sulfate solution: Weigh 50 g of ferric sulfate, add 200 ml of water to dissolve, and then 100 ml of sulfuric acid, and then dilute to 1000 ml with water.

Fourth, the operation method:

1, sample processing:

Weigh 2-5 grams of sample, placed in a funnel with folded filter paper, first wash the fat with 50 ml of ether 5 times, then wash the soluble sugar with about 100 ml of 85% ethanol, and transfer the residue to 250 ml. In a beaker, wash the filter paper and funnel with 50 ml of water, wash the solution into the beaker, heat the beaker on a boiling water bath for 15 minutes, gelatinize the starch, let cool to below 60 ° C, add 20 ml of amylase solution, at 55- Incubate at 60 ° C for 1 hour and mix constantly. Then take 1 drop of this solution and add 1 drop of solution, should not appear blue, if it is blue, then heat the gelatinization and add 20 ml of amylase solution, continue to keep warm until the iodine does not appear blue. Heat to boiling, cool and transfer to a 250 ml volumetric flask, add water to the mark, mix, filter, discard the initial filtrate. Take 50 ml of the filtrate, place it in a 250 ml Erlenmeyer flask, add water to the mark, reflux for 1 hour in a boiling water bath, add 2 drops of methyl red indicator solution after cooling, and neutralize to neutral with 20% sodium hydroxide solution. Transfer the solution to a 100 ml volumetric flask, wash the conical flask, wash the solution into a 100 ml volumetric flask, add water to the mark, and mix for later use.

B, measurement:

Pipette 50 ml of the treated sample solution, add 25 ml of alkaline copper tartrate solution and 25 ml of ethyl acetate in a 400 ml beaker, cover a beaker on the beaker, heat, control, and boil in 4 minutes, then accurately Boil for 2 minutes, use asbestos-plated Gushi or c4 to melt the filter, and wash the beaker and precipitate with 60 °C hot water until the wash is not alkaline. Put the sputum or sputum back into the original 400 ml beaker, add 25 ml of ferric sulphate solution and 25 ml of water, stir with a glass rod to completely dissolve the cuprous oxide, and titrate with 0.1000 N potassium permanganate standard solution. Red is the end point.

At the same time, take 50 ml of water and the same amount of amylase solution as the sample is processed, according to the same method.

Do a reagent blank test.

Calculation: X1 = ((A1 - A2) × 0.9) / ( m1 × 50 / 250 × V1/100 × 1000) × 100

X1: the content of starch in the sample, %;

A1: content of reducing sugar in the sample for measurement, mg;

A2: the content of reducing sugar in the reagent blank, mg;

0.9: conversion factor of reducing sugar (calculated as glucose) into starch;

M1: weighing the sample, g;

V1: volume of the sample processing solution for measurement, ml (m1).

Second method acid hydrolysis

First, the principle:

After the sample is removed from fat and soluble sugars, the starch is hydrolyzed with acid to a reducing monosaccharide, which is then determined by reducing sugar and converted into starch.

Second, the reagent:

1, ether;

2, 85% ethanol solution;

3, 6N hydrochloric acid solution;

4, 40% sodium hydroxide solution;

5, 10% sodium hydroxide solution;

6, methyl red indicator solution: 0.2% ethanol solution

7, precision PH test paper

8, 20% lead acetate solution

9, 10% sodium sulfate solution

10, ether

11, alkaline tartaric acid copper liquid. (Preparation before seeing)

12. Alkaline tartrate copper ethate; (preparation before seeing)

13, iron sulfate; (preparation see before)

14, 0.1000N potassium permanganate standard solution

Third, the instrument:

1, water bath

2. High-speed tissue masher: 1200r/min

3. A saponification unit with a 250 ml Erlenmeyer flask.

Fourth, the operation method:

1, sample processing

A, food, beans, cakes, biscuits and other drier samples, weigh 2.0-5.0 grams of milled 40 mesh sieve sample, placed in a funnel with slow filter paper, washed with 30 ml of ether three times The fat in the sample was discarded. The residue was washed several times with 150 ml of 85% ethanol solution to remove soluble sugars. The ethanol solution was filtered off, and the residue in the funnel was washed with 100 ml of water and transferred to a 250 ml Erlenmeyer flask, 30 ml of 6N hydrochloric acid was added, the condensed tube was connected, and refluxed for 2 hours in a boiling water bath. Immediately after the reflux is completed, the water is cooled in the running water. After the sample hydrolyzate is cooled, add 2 drops of methyl red indicator solution, first adjust to yellow with 40% sodium hydroxide solution, and then calibrate with 6N hydrochloric acid until the hydrolyzate just turns red. If the hydrolysate is darker in color, it can be tested with a precision pH test paper so that the pH of the sample hydrolysate is about 7. Then add 20 ml of 20% lead acetate solution, shake well and let stand for 10 minutes. Add 20 ml of 10% sodium sulfate solution to remove excess lead. After shaking, transfer all the solution and residue into a 500 ml volumetric flask, wash the conical flask with water, combine the washing solution into a volumetric flask, and dilute to the mark with water. After filtration, 20 ml of the initial filtrate was discarded, and the filtrate was used for measurement.

B, vegetables, fruits, all kinds of grain and water-containing cooked food products: according to 1:1 water in the tissue mincer into a homogenate (vegetables, fruits need to wash, dry, take the edible part) weighed 5- 10 g of homogenate (liquid sample can be directly weighed), in a 250 ml Erlenmeyer flask, add 30 ml of diethyl ether to shake and extract (removal of fat in the sample), filter with filter paper to remove ether, then rinse with 30 ml of ether twice Discard the ether. The following operation according to A from "reuse 150 ml of 85% ethanol solution".

2. Determination:

Pipette 50 ml of the treated sample solution into a 400 ml beaker, add 25 ml of alkaline copper tartrate solution and 25 ml of B solution. Cover the beaker with a surface dish and heat it. Control it to boil for 4 minutes and then boil it accurately for 2 minutes. Drain it with asbestos-coated Gushi or G4, and wash the beaker and sediment with 60 °C hot water. The liquid is not alkaline. Put the sputum or sputum back into the original 400 ml beaker, add 25 ml of ferric sulphate solution and 25 ml of water, stir with a glass rod to completely dissolve the copper oxide, and set the droplet to 0.10 N potassium permanganate to reddish As the end point.

At the same time, take 50 ml of water, add the same amount of alkaline copper tartrate and sulfur, sulfur

The acid iron solution and water were subjected to the reagent blank test in the same manner.

Calculation: x2=((A3-A4)×0.9)/( M2×V2/500×100)------------------------×100