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Some simple field tests for use in food inspections.

In the world of portable electronic monitoring devices, sophisticated color comparitors, and various and sundry test strips, none are made specifically as screening tests for certain esoteric issues, as well as for certain mundane ones, that we face in food protection and sanitation. When we first started in this industry as field sanitarians, part of our "sampling equipment" consisted of a few screening tools that are not available commercially but that nonetheless served us quite well. Although these simple field tests were homemade, they had a degree of sophistication needed to serve us both as enforcement and as educational tools. It seems a shame that they have all but disappeared from regular use. We would like to reintroduce a few of these tests that you, the practicing sanitarian, may find quite useful in your routine inspections. Just one word of caution about their use: In cases where certain findings lead to legal procedures, such findings must be corroborated by tests done in a qualified laboratory on samples correctly collected, shipped, identified, and otherwise handled. Therefore, for legal purposes, these field tests are not valid. Remember that field tests are made only for screening samples. Having said that, we present you with a few of our favorites. More will follow in future articles.

Detection of Spoilage of Shucked Oysters


A pH test strip indicator paper that measures pH at least between 4.0 and 8.0.


Immerse the pH indicator test strip in the oyster liquid for about five seconds to cover all the colors on the paper. Shake off the excess liquid and match the color of the wet indicator with the comparison colors for pH value.


Fresh-shucked oysters have a pH between 6.0 and 7.0. A pH of 5.4 to 5.8 is suspect, and values below this range suggest decomposition. If you suspect that the oysters were recently washed, lay the pH test strip directly on the oysters, or, if available, use several drops of a pH liquid indicator (available in hardware or garden stores) or methyl-red indicator solution. The color change will show the pH of the oyster. If the methyl-red solution remains red, spoilage may be present.

Detection of Sulfites in Meat Products


* 4-inch squares of wax or white butcher paper,

* dropper bottle containing a 0.02 percent aqueous solution of malachite green, and

* toothpicks or wooden tongue depressors.


1. Place about one-half teaspoonful of the suspect meat on the wax or butcher paper.

2. Add about 0.5 mL (one dropperful) of malachite-green solution to the meat.

3. Thoroughly mix the meat and dye for about one to two minutes with the toothpick or tongue depressor.


Meat containing sulfites will decolorize the dye, and the meat will resume its bright red color. Meat not adulterated with sulfites will remain a dark bluish green. The malachite-green dye solution remains stable for several weeks, particularly if it is kept in a polyethylene vial with a polyethylene dropper and neoprene bulb.

Detection of Washed Eggs


* distilled or deionized water,

* microscope slides, and

* 0.1N solution of silver nitrate.


A drop of distilled or deionized water is placed on the shell of an egg. After a few moments, remove the drop and place it on the microscope slide. Add one drop of the 0.1N silver nitrate solution and examine for the presence of precipitate.


Clean, unwashed eggs contain both potassium and chlorides on the exterior of the shell. If the solution produces a precipitate, that shows that chlorides are present. If further screening confirmation is necessary, add a second drop of a 0.1N solution of cobalt nitrate to the slide; crystals will form within 20 minutes, showing the presence of potassium. If no precipitate is formed, it is a good indication that the eggs were washed.

The malachite dye solution used for the detection of sulfites in meat products is also useful in finding scraped, abraded, or sandblasted eggs through immersion of the egg in the dye solution. The dye discolors proteinaceous material that normally covers eggshells. Unstained spots show that the proteinaceous film has been removed.

Detection of Cereal Adulterants in Ground Meat or Meat Products Materials

* a 50-mL beaker or a small glass jar,

* distilled or deionized water,

* filter paper,

* a vial of tincture of iodine (available at most pharmacies), and

* a teaspoon.


1. Place several ounces of ground meat or meat product in the beaker or jar.

2. Add enough distilled or deionized water to separate the particles and stir well.

3. Place some of the floating material on a filter paper.

4. Put several drops of tincture of iodine solution on the particles.

5. Let stand for a minute or two.


The appearance of a bluish or purplish color is an indication that cereal may be present.

The iodine solution is also useful for detecting cereal adulteration of coffee. When testing coffee, use about 10 cc of both coffee and water. After stirring, add five to 10 drops of the iodine solution. A color change to blue or purple suggests the presence of cereal adulterants.

Other Tools?

If anyone uses any other simple field tools and wishes to share them with our readers, please write to the authors at Tools for EH, NEHA, 720 S. Colorado Blvd., South Tower, Suite 970, Denver, CO 80246.
COPYRIGHT 1998 National Environmental Health Association
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1998, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
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Author:Balsamo, James J., Jr.
Publication:Journal of Environmental Health
Date:Jan 1, 1998
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