The issue of melamine in pet food has come up again as more lots of pet food are found to be contaminated with it.  At least a few news outlets have published a proposed reason for this contamination by a monomer from another industrial sector.  Melamine is very nitrogen rich- 6 equivalents per mole- so if you spike grain products with it you can cause the nitrogen analysis to read higher than it normally would.  Protein content is one of the factors in the pricing of animal feed, so an additive that would contribute to an uptick in nitrogen content would raise the price or even make a non-saleable lot of feed qualify for sale. 

The nitrogen test that most people think of is the Kjeldahl test.  It is a digestion-distillation-titration method that affords total nitrogen.  This test is still in wide use and is inexpensive to conduct.  A friend who has an Ag Lab still does the test on a bank of burners in his lab for total nitrogen in feed samples.

The practice of adulteration of foodstuffs not limited to China.  As an undergraduate I worked in a dairy processing plant lab and we had to screen for several kinds of mischief.  Dilution of milk with water is an old trick, given that pricing is on a per pound basis, so we had to test each raw milk tanker for total solids content.  We also tested for pH and temperature.

Neutralization of partially fermented raw milk with NaOH was also practiced at one time, so we taste tested each tanker as well since neutralization could not mask off-flavor.  Finally, we had to carefully screen raw milk for residual antibiotics.  Mastitis is an inflamation of the udder and has many causes. One aggravating factor is the common practice of milking ol’ Bessie three times a day.  A sick cow has to be taken off-line to recover. This reduces the productivity of the cow.

Farmers were often tempted to give sick cows a big jolt of antibiotic and get her milking again before the time needed to fully recover and clear the system of antibiotic. This could lead to antibiotic contamination in the tanker.  We performed two tests for penicillin at our plant. The microbiological test we performed was the Bacillus stearothermophilus disk assay. The other was a radiological assay called the Charm test utilizing C-14.  This test could be performed in 20 minutes, whereas the B. stearothermophilus test took 6 hours or so.  The newer Charm tests now take only a few minutes.

Residual antibiotics found in dairy products on the Grocers shelf could put a dairy out of business for repeated infractions. The state health authorities took (take) a dim view of penicillin in milk.