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    Home > Chemicals Industry > Chemical Technology > Determination of bleaching agent in food (1)

    Determination of bleaching agent in food (1)

    • Last Update: 2021-07-11
    • Source: Internet
    • Author: User
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    Bleaching agents refer to food additives that destroy or inhibit food color factors, make them fade or prevent browning
    .


    The bleaching agents commonly used in food are mostly sulfurous acid and its salts, which bleach food through the reduction of sulfur dioxide produced by it, and also have antibacterial, anti-corrosion and anti-oxidation effects


    (1) Principle Sulfite reacts with sodium tetrachloromercury to form a stable complex, and then reacts with formaldehyde and pararosaniline hydrochloride to form a purple-red complex.
    The color depth is proportional to its concentration within a certain range, and it is quantitative compared with the standard series.

    .

    (2) Reagent

    ①Sodium tetrachloromercury absorption solution: Weigh 13.
    6g of mercuric chloride and 6.
    0g of sodium chloride , dissolve in water and dilute to 1000mL, leave it overnight, and filter for use
    .

    ② Ammonium sulfamate solution (12g/L): Weigh 1.
    2g of ammonium sulfamate in a 50mL beaker, transfer to a 100mL volumetric flask with water, and make a constant volume
    .

    ③ formaldehyde solution (2g / L): lessons 0.
    55mL precipitation polymerization without formaldehyde (36%), diluted with water to 100mL, and mix
    .

    ④ Starch indicator solution: Weigh 1g of soluble starch, mix it into a paste with a little water, slowly pour it into 100mL of boiling water, stir with the addition, boil, and let it cool for later use
    .


    The indicator liquid is temporarily prepared


    ⑤ Potassium ferrocyanide solution: Weigh 10.
    6g of potassium ferrocyanide [K 4 Fe(CN) 6 ·3H 2 O], add water to dissolve and dilute to 100 mL
    .

    ⑥ Zinc acetate solution: Weigh 22g of zinc acetate [Zn(CH 3 COO) 2 ·2H 2 O] and dissolve it in a small amount of water, add 3 mL of glacial acetic acid, and dilute to 100 mL with water
    .

    ⑦ Pararosaniline hydrochloride solution: Weigh 0.
    1g of pararosaniline hydrochloride in the research body, add a small amount of water to grind to dissolve and dilute to 100mL
    .


    Take out 20mL, place it in a 100mL volumetric flask, add hydrochloric acid (1+1), shake well to make the solution change from red to yellow, if it does not turn yellow, add a small amount of hydrochloric acid until yellow appears, then add water to dilute to the mark, and mix well Standby (if there is no hydrochloric acid pararosaniline can be replaced by fuchsin hydrochloride)


    ⑧Iodine solution [c(1/2I 2 )=0.
    100mo/L]
    .

    ⑨Sodium thiosulfate standard solution [c(Na 2 S 2 O 3 ·5H 2 O)=0.
    100mol/L]
    .

    ⑩Sulfur dioxide standard solution: Weigh 0.
    5g sodium bisulfite, dissolve it in 200mL sodium tetrachloromercury absorption solution, let it stand overnight, and filter the supernatant with quantitative filter paper for later use
    .



    The concentration of sulfur dioxide standard solution is calculated as follows:

    Where x——the concentration of sulfur dioxide standard solution, mg/mL

    V 1 ——Determine the volume of sodium thiosulfate standard solution consumed by sodium bisulfite-sodium tetrachloromercury solution, mL

    V 2 -reagent blank consumption of sodium thiosulfate standard solution volume, mL

    c——Concentration of sodium thiosulfate standard solution, mol/L

    32.


    03——Every 1mL sodium thiosulfate [c(Na 2 S 2 O 3 ·5H 2 O)=1.


    ⑪Sulfur dioxide use liquid: before use , dilute the standard sulfur dioxide solution with sodium tetrachloromercury absorbing liquid to the equivalent of 2ug sulfur dioxide per 1mL
    .


    This liquid is stored in a refrigerator at 4°C and can be used within one week


    ⑫ Sodium hydroxide solution (20g/L)


    ⑬Sulfuric acid (1+71)


    (3) Instrument spectrophotometer


     

     

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