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    Home > Chemicals Industry > Chemical Technology > Other methods of reducing sugar determination

    Other methods of reducing sugar determination

    • Last Update: 2021-07-18
    • Source: Internet
    • Author: User
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    The potassium permanganate titration method (according to the second method of GB/T5009.
    7-2008) is introduced here
    .

    1.
    Principle

    A certain amount of the protein- removed sample solution is completely reacted with excess alkaline copper tartrate , reducing sugars to generate quantitative cuprous oxide precipitation
    .


    After filtration and washing the precipitate, dissolving ferric sulfate solution with an excess of an acidic cuprous oxide , ferric sulfate is quantitatively reduced to ferrous sulfate :

    A Cu 2 O + of Fe 2 (SO .
    4
    ) .
    3
    + H 2 SO .
    4
    = 2CuSO .
    4
    + 2FeSO .
    4
    + H 2 O

    Then use potassium permanganate standard solution to titrate the ferrous sulfate produced, and the end point is pink
    .

    10FeSO .
    4
    + 2KMnO .
    4
    + 8H 2 SO .
    4
    = 5Fe 2 (SO .
    4
    ) .
    3
    + K 2 SO .
    4
    + 2MnSO .
    4
    + 8H 2 O

    According to the consumption of potassium permanganate standard solution, calculate the quality of cuprous oxide, and then check the " quality table of cuprous oxide equivalent to glucose, fructose, lactose, and invert sugar" (see appendix 5) to get the equivalent of reducing sugar To calculate the reducing sugar content in the sample
    .


    The calculation formula is as follows:


    Where x——the mass of reducing sugar in the sample is equivalent to the mass of cuprous oxide , mg

    V——Determine the volume of potassium permanganate standard solution consumed by the sample solution, mL

    V 0 ——The volume of potassium permanganate standard solution consumed in the blank test, mL

    c—— The concentration of potassium permanganate standard solution, mol/L

    71.


    54——1mL potassium permanganate standard solution [c(1/5KMnO 4 )=0.


    X 2 ——Reducing sugar content in the sample, g/100g

    m 3 ——The mass equivalent to reducing sugar obtained from X 1 in Appendix 5, mg

    m 4 ——the mass of the sample, g

    V 1 ——Volume of test sample solution, mL

    250——The total volume of the sample after processing, mL

    2.
    Tips

    (1) This method has high accuracy and good reproducibility, and its accuracy and reproducibility are better than direct titration method.
    It is suitable for the determination of reducing sugars in various foods, and the colored sample solution is not limited
    .


    However, the operation of this method is complicated and time-consuming, and a special search table is required


    (2) The measurement must be carried out in strict accordance with the specified operating conditions
    .


    Control the intensity of the heat source to ensure that it is heated to boiling within 4 minutes, and the boiling time must also be controlled within 2 minutes, otherwise the error will be large


    (3) Since the alkaline copper tartrate solution used is excessive, the boiled solution should remain blue (potassium sodium tartrate copper complex ion)
    .


    If it does not show blue, it indicates that the sugar concentration in the sample solution is too high.


    (4) During the entire process of filtering and washing the cuprous oxide precipitation, the precipitate should always be below the liquid surface, and the upper layer of the precipitation should be kept a layer of water to isolate the air and prevent the cuprous oxide from being oxidized when exposed to the air
    .

    (5) Alkaline copper tartrate A and B solutions should be stored separately and mixed in equal amounts before use to avoid the slow reduction of copper hydroxide in the alkaline solution by potassium and sodium tartrate and the precipitation of cuprous oxide, which will affect the accuracy of the measurement
    .

    (6) Commonly used clarifying agents during sample processing include neutral lead acetate solution, zinc acetate and potassium ferrocyanide solution, copper sulfate and sodium hydroxide solution
    .


    When lead acetate is used as a clarifying agent, if lead ions remain in the sample solution, it will combine with fructose to make the measurement result lower.


    (7) The refined asbestos laid in the ancient crucible or the G4 vertical melting crucible must be dense to avoid the loss of cuprous oxide precipitation
    .

    (8) When the reducing sugar in the sample includes both monosaccharides and disaccharides such as maltose or lactose, the measurement result of reducing sugars will be lower.
    This is mainly because the disaccharide molecule contains only one reducing group
    .

    (9) The reaction process of reducing sugar and alkaline copper tartrate solution is very complicated.
    In addition to proceeding according to the aforementioned reaction formula, it is also accompanied by side reactions
    .


    In addition, different reducing sugars have different reducing abilities, and the amount of cuprous oxide produced by the reaction is also different


    Related link: Determination of reducing sugar in candy (2)

     

     

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