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Determination of sucrose and total sugar in food

2023-12-25 16:07

In food production, in order to determine the maturity of raw materials, identify the quality of food raw materials such as white sugar and honey, and control the quality indicators of products such as candies, preserved fruits, and sweetened dairy products, it is often necessary to measure the content of sucrose. There are two methods for determining sucrose: high-performance liquid chromatography and acid hydrolysis. For high-purity sucrose solutions, physical testing methods such as relative density method, refractive index method, and optical rotation method can be used to determine. This only introduces the acid hydrolysis method (according to GB/T5009.8-2008).

(1) After degreasing the principle sample, it is extracted with water or ethanol. The extraction solution is clarified to remove impurities such as protein, and then hydrolyzed with hydrochloric acid to convert sucrose into reducing sugar

Measure the content of reducing sugar in the sample solution before and after hydrolysis using the method of reducing sugar determination. The difference between the two is the content of converting sugar (the amount of reducing sugar produced by sucrose hydrolysis), which is multiplied by a conversion coefficient of 0.95 (i.e., the content of sucrose).

(2) Reagents

① Hydrochloric acid (1+1): Take 50ml of hydrochloric acid and slowly add it to 50mL of water. After cooling, mix well.

② Methyl red indicator solution (1g/L): Weigh 0.1g of methyl red, dissolve it in a small amount of ethanol, and make up to 100mL.

③ Sodium hydroxide solution (200g/L): Weigh 20g of sodium hydroxide and dissolve it in water. Let it cool and make up to 100mL.

④ The other reagents are the same as direct titration or potassium permanganate titration.

(3) The instrument is the same as direct titration method or potassium permanganate method.

(4) Take a certain amount of sample and process it using direct titration or potassium permanganate titration. Take 50ml each of the processed samples and place them in 100mL volumetric flasks. Add 5mL of hydrochloric acid solution (1+1) to one part, heat in a water bath at 68-70 ℃ for 15 minutes, remove and quickly cool to room temperature, add 2 drops of methyl red indicator solution, neutralize with sodium hydroxide solution (200g/L) to neutral, add water to the mark, shake well.

Dilute the other portion directly with water to 100mL and determine the reducing sugar content using direct titration or potassium permanganate titration.

(5) The results are calculated using the direct titration method to determine the glucose content in the sample using the following formula:

In the formula, w - the content of sucrose in the sample, g/100g

M1- Mass of reducing sugar in unhydrolyzed sample solution, mg

M2- Mass of reducing sugars in the hydrolyzed sample solution, mg

V1- Total volume of sample processing solution, mL

V2- Determine the volume of sample processing solution used for reducing sugar extraction, ml

M - Sample mass, g

0.95- Coefficient for converting reducing sugar (calculated as glucose) to sucrose

When the sucrose content is ≥ 10g/100g, retain three significant figures in the calculation result; When the sucrose content is less than 10g/100g, the calculation result should be rounded to two significant digits (i.e. the calculation result should be rounded to one decimal place).

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