Determination of starch in food

Starch content is the main quality indicator of certain foods, and it is a common analysis item in food production management
.

The commonly used methods for determination are enzymatic hydrolysis and acid hydrolysis, which are based on the hydrolysis of starch into glucose under the action of enzymes or acids, and then measure it according to the reducing sugar measurement method, and then convert it into starch content

1.
Principle

After the samples are respectively used diethyl ether or petroleum ether to remove fat and ethanol to remove soluble sugars, the starch is hydrolyzed into low molecular dextrin and maltose under the action of amylase , and then further hydrolyzed with hydrochloric acid to obtain the final hydrolysate glucose:

Then it is measured according to the reducing sugar measurement method, and the result is multiplied by the conversion factor 0.

9 (that is, 162n/180n), which is the starch content

Where x——the starch content in the sample, g100g

m ₁ ——the mass of glucose in the test sample (sample hydrolysate), mg

m ₂ ——the mass of glucose in the reagent blank, mg

m——Weigh the mass of the sample, g

V——Volume of sample treatment liquid (hydrolyzate) for measurement, mL

0.

9-conversion factor for converting glucose into starch

The calculation result is kept to one decimal place
.

2.
Tips

(1) Amylase has specificity and selectivity.
It can only hydrolyze starch into maltose, but not other polysaccharides.
After hydrolysis, other polysaccharides can be filtered out, so enzymatic hydrolysis is not affected by polysaccharides such as hemicellulose and pectin.
The interference is suitable for other samples with high polysaccharide content
.

The results are accurate and reliable, with good reproducibility, but the stability of enzyme catalytic activity is greatly affected by pH and temperature, and the operation is cumbersome and time-consuming, and its use is limited to a certain extent

(2) Fat will hinder the effect of enzyme on starch and the removal of soluble sugar, so it should be removed with ether or petroleum ether first
.

When the fat content in the sample is small, the operation of dissolving and washing away the fat with ether can be omitted

(3) The sample is first used to remove fat with ether or petroleum ether , and then 85% ethanol is used to remove soluble sugars to prevent starch from being washed away along with soluble sugars
.

(4) Before using amylase, determine its activity and the amount added during hydrolysis
.

Use a little starch solution of known concentration, add a certain amount of amylase solution, keep it in a water bath at 55～60℃ for 1h, use iodine solution to check whether the starch is completely hydrolyzed to determine the enzyme activity and the amount of hydrolysis

(5) Starch grains have a lattice structure, which is difficult for amylase to act.

(6) The condenser tube of the reflux device should be longer to ensure that the hydrochloric acid will not volatilize during the hydrolysis process and maintain a certain concentration

(7) The hydrolysis procedure of starch and the color reaction of iodine are as follows:

Hydrolysis procedure: starch → blue dextrin → red dextrin → achromatic dextrin → maltose → glucose

Color reaction: purple blue→blue→red→colorless→colorless→colorless

Related Links: Determination of Sucrose and Total Sugar in Food