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    Home > Chemicals Industry > Chemical Technology > Other methods for determining fat in food (1)

    Other methods for determining fat in food (1)

    • Last Update: 2021-07-18
    • Source: Internet
    • Author: User
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    1.
    Rhodes-Gotheli method (alkaline ether extraction method) (according to GB 5413.
    3-2010)

    This method is adopted by the International Organization for Standardization (ISO), the Food and Agriculture Organization of the United Nations/World Health Organization (FAO/WHO), etc.
    , and is an international standard method for the quantification of lipids such as milk and dairy products
    .

    (1) Principle Use ammonia- ethanol solution to destroy the colloidal properties and fat globule membrane of the milk, so that the non-fat components are dissolved in the ammonia- ethanol solution and the fat is freed.
    The alkaline hydrolysate of the sample is extracted with ether and petroleum ether , and the sample is distilled.
    Or evaporate to remove the solvent and determine the quality of the extract dissolved in the solvent
    .

    (2) Reagents Unless otherwise specified, the reagents used in this law are of analytical grade or above, and the water is the third-grade water specified in GB/T6682-2008
    .

    ①Amylase: Enzyme activity ≥1.
    5U/mg
    .

    ②Ammonia: The mass fraction is about 25% (ammonia with a higher concentration can be used)
    .

    ③ ethanol : volume fraction of at least 95%
    .

    ④ Ether : does not contain peroxides, does not contain antioxidants, and meets the requirements of the test
    .

    ⑤Petroleum ether : boiling range 30~60℃
    .

    ⑥Mixed solvent: mix diethyl ether and petroleum ether in equal volume and prepare before use
    .

    ⑦Iodine solution: about 0.
    1mol/L
    .

    ⑧ Congo red solution (C 32 H 22 Na 6 Na 2 O 6 S 2 ): Dissolve 1 g of Congo red in water and dilute to 100 mL
    .

    ⑨ Hydrochloric acid (6mol/L): Measure 50mL of 12mol/L hydrochloric acid and slowly pour it into 40mL of water, dilute to 100mL, and mix
    .

    (3) Instruments

    ①Analytical balance: Sensitivity is 0.
    1mg
    .

    ② Centrifuge: It can be used to place liposuction bottles or tubes, and the speed is 500~600r/min
    .

    ③ Electric heating constant temperature water bath
    .

    ④ Oven
    .

    ⑤ bottle liposuction: liposuction bottles with cork or other stopper should not affect the use of a solvent (e.
    g.
    , silica gel or poly tetrafluoroethylene )
    .


    Cork stoppers should be immersed in ether first , and then placed in water at or above 60°C for at least 15 minutes, and used after cooling


    (4) Operation steps

    ①Preparation of the fat collection bottle: Add a few zeolite to the dry fat collection bottle and put it in an oven to dry for 1 hour
    .


    Then cool the fat collection bottle to room temperature and weigh it to the nearest 0.


    ②Blank test: Use 10mL of water instead of the sample for a blank test
    .

    ③Determination:

    a.
    Precisely suck (weigh) a certain amount of sample (10.
    00mL milk; 1~5g milk powder, dissolved in 10mL 60℃ water) into a liposuction bottle
    .

    b.
    Add 2.
    0mL ammonia water, and immediately put the liposuction bottle into a water bath at (65±5)℃ after mixing thoroughly, and heat for 15-20min (take out and shake from time to time)
    .


    Take out and cool to room temperature


    c.
    Add 10 mL of ethanol and mix gently but thoroughly to avoid the liquid getting too close to the bottleneck
    .


    If necessary, add two drops of Congo Red solution


    d.
    Add 25mL ether , plug the bottle stopper, keep the liposuction bottle in a horizontal position, clamp the extended part of the small ball upwards to the shaker, shake at about 100 times/min for 1 minute, or manually shake , But care should be taken to avoid the formation of permanent emulsions
    .


    After the liposuction bottle is cooled, carefully open the stopper, rinse the stopper and the bottle neck with a small amount of mixed solvent, so that the rinsing fluid flows into the liposuction bottle


    e.
    Add 25 mL of petroleum ether, plug the re-wet stopper, and gently shake for 30 seconds as described in d
    .

    f.
    Put the stoppered liposuction bottle into a centrifuge and centrifuge at 500~600r/min for 5min
    .


    Or let the liposuction bottle stand for at least 30 minutes until the upper layer is clear and clearly separated from the water phase


     

     

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