Measurement of sugar content in food

Determination method of sugar

There are many methods for measuring sugar, which can be roughly divided into three categories

1. Physical method: (1. Optical rotation method, 2. Refractive method, 3. Specific gravity method,)

2. Physical and chemical methods: (1. Point method, 2-pole method, 3. Photometric method, 4. Chromatographic method)

3. Chemical methods: (1. Felling's method, 2. Potassium permanganate method, 3. Iodometric method, 4. Potassium ferrocyanide method, 5. Anthracene copper colorimetric method, 6. Carbazole colorimetric method)

There are three types in total, and when measuring other carbohydrates, they are often hydrolyzed into sugars before being measured.

Determination of total sugar

The total sugar in food mainly refers to reducing glucose, fructose, pentose, lactose, and sucrose (hydrolyzed to 1 molecule of glucose and 1 molecule of fructose) that can be hydrolyzed into reducing monosaccharides under test conditions, maltose (hydrolyzed to 2 molecules of glucose), and possibly partially hydrolyzed starch (hydrolyzed to 2 molecules of glucose). The reason why reducing sugars have reducing properties is due to the presence of free aldehyde groups (- CHO) or ketone groups (=C=O) in the molecules. The classical chemical methods for determining total sugar are based on their ability to be oxidized by various reagents. Among these methods, various improved methods based on the oxidation of Fehling's solution have the widest application range.

Here, we mainly introduce the potassium ferrocyanide method, anthracene copper colorimetric method, and Fehling's volumetric method. Due to its complex reaction and multiple influencing factors, the Fehling volumetric method is not as accurate as the potassium ferrocyanide method. However, its operation is simple and rapid, and the reagent is stable, so it is widely used. The anthracene copper colorimetric method requires the concentration of sugar solution to be within a certain range during colorimetry, but requires the detection solution to be clear. In addition, in most cases, the determination requirement does not include starch and dextrin, which requires the removal of starch and dextrin before measurement, making the operation complex and limiting its widespread application.

Determination method of reducing sugar

Reducing sugars include glucose, fructose, and maltose. Glucose molecules contain bruised aldehyde stems, fructose molecules contain bruised ketone stems, and lactose and maltose molecules contain bruised semi carboxylic stems, all of which have reducing properties. When measuring reducing sugars, all methods of hydrolyzing sugars into inverting sugars and then measuring total sugars can be used to determine reducing sugars.

Feilin's capacity method

The principle, reagents, and method of this method are the same as the method for determining total sugar. The sample solution does not need to be overconverted, but can be directly titrated with the filtrate. The filtrate should be titrated with a reducing sugar content of 0.2-0.5%, which can be adjusted by increasing or decreasing the sample volume or changing the dilution ratio.