Thử thịt bị tẩy (và khác thức ăn khác)

[VinhL]

Các loại thuốc dùng bất hợp pháp để tẩy thịt đều thuộc dạng Sulfite:
Na2SO3: Sodium Sulfite
K2SO3: Potassium Sulfite
Na2HSO3: Sodium HydroSulfite
KHSO3: Potassium HydroSulfite

Để phòng ngừa mua lầm các loại thực phẩm đã được tân tạo với hóa chất Sulfite, thì thể sử dụng Sulfite Test.

Hiền nay có nhiều công ty bào chế Sulfite Test
1) Mercoquant 110013 của hảng Merck Millipore
Merck Sulphite Test Strips "Mercoquant 110013". They cost $70.00 plus GST plus $35 freight = $112.00 for 100 tests.

[IMG]http://www.chemdat.merck.de/is-bin/intershop.static/WFS/Merck-SE-Site/Merck/en_US/product/images/117925_mqarsen.jpg[/IMG]
The sulfite test is suitable for food analysis, particularly in the testing of wine and fruit juices, sulfurated foods (e.g. fresh and dried fruits), fish shellfish, crustaceans and minced meat products.

http://www.chemdat.merck.de/sweden/c...search+results

Nên đọc thêm:
http://www.fedupwithfoodadditives.in.../sulphites.htm
Trích:
DETAILS OF HOW TO USE THE TEST STRIPS
You have sulphite test-strips. Their active end, which you put into the meat and don't touch with your fingers, has a small white square on it. There is a colour scale on the outside of the in the plastic bag.
In addition, you will need the following, all rinsed and dried thoroughly between uses: Measuring teaspoon, Small glass tumbler, Small fork, Chilled water, Knife.
Buying the meat samples
Best to buy the samples fresh, keep cool and test as soon as you get home. Friday afternoon is a good time because those butchers who use sulphites illegally often wait until the inspectors are unlikely to call. Ask for 250g. Make sure that you label the bag with the date and name of the butcher so there can be no mix-ups.
Testing the meat sample.
1. Put two teaspoons of chilled water into the tumbler.
2. Slash open the plastic bag containing meat. Make a diagonal cut in it with a clean knife to expose the centre of the meat. Scoop out a teaspoon full from one end of the cut surface, level with the knife if needed, and drop into the tumbler. Repeat, taking the sample from the other end of the cut surface.
3. Thoroughly macerate the mince and chilled water with the fork so that it is a uniform sludge. This takes about 15 seconds to do properly.
4. Without touching the active end of the Sulphite test strip, dip the active end into the mince sludge for one second. Make sure that it is thoroughly wetted by wriggling it around.
5. Take out of the sludge, flick clean and time exactly 30 seconds. You can rinse briefly with cool water to get any meat off the active end.
6. Compare the colour of the active end with the colour scale supplied. Put the active end and the colour scale side by side and try the next higher and the next lower to be certain.
7. Write down the reading. Note that meat contains some sulphites anyway from the high level of protein, so some pink colour is expected.
8. Don't panic if you get 80ppm. The calculation is to take 80 from the reading and then multiply by 2. Therefore a reading of 80 is 0 ppm. A reading of 180ppm is 200ppm after correction. ppm means parts per million.
Rapid strip test
Sulphite test strips (Merckoquant strips, Merck Pty Ltd) are available
commercially. Briefly, 10g of minced meat is mixed in 20 mL of water,
filtered and the resulting filtrate is adjusted to pH 12 with 1 M NaOH. A
strip is dipped into the filtrate and examined against a colour scale to
give an approximate value. They can be used, and have been used, by
concerned individuals; however, the manufacturer acknowledges that
this method can have interference from the cysteine or glutathione in
the meat which will give a false positive.

2) Sulfite test paper from CTL Scientific Supply Corp.
[IMG]http://www.ctlscientificsupply.com/productimg/90763pic.gif[/IMG]
Pack Size: box of 100 strips
Hazard Class /UN Number: Not Restricted
Storage Temp: Room Temperature

This test paper is recommended for the rapid detection of sulphites and gaseous sulphur dioxide. The white paper turns pink to brick-red in the presence of sulphite or free sulphur dioxide. The paper does not react with sulphites in acidic solutions. These have to be neutralized with solid sodium acetate. Thio-sulphates only interfere with the determination of gaseous sulphur dioxide.Limit of sensitivity: 10 mg/l Na 2 SO 3Note: sulphite test paper can also be used for medical-diagnostic purposes as a rapid test for sulphite oxidase deficiency.

http://www.ctlscientific.com/cgi/dis...item_num=90763