Sundlof says that the fact that melamine has turned up in all three of these proteins lends "credibility'' to theories that it was intentionally introduced. "That will be one of the theories we will pursue when we get into the plants in China," he says. The FDA's Elder adds that, "the shipment of an adulterated product" is illegal under the Food, Drug and Cosmetics Act of 1938, and anyone found to be in violation of the law could face criminal prosecution and penalties.

According to Lora Sporny, a professor of nutrition education at Columbia University, protein is the only source of nitrogen in food. "Whenever someone looks at nitrogen in food, almost always they are looking at the amount of protein in food," she explains. Sundlof concurs, telling Scientific American yesterday that, "Traditionally the way that food firms have analyzed for protein is by looking for total nitrogen. Maybe that's something that needs to be changed in light of this outbreak."

According to Ron Salter, a vice president at Wilbur-Ellis, his company did an early spot check on a shipment of rice gluten from its new Chinese supplier shortly after hooking up with the company in the summer of 2006. He declined to comment on the depth of the analysis, other than to say that it checked for levels of protein ash, moisture and fiber. He says the rice gluten was purchased based on an agreed-on minimum amount of protein content, although, he adds, that he does not buy products based solely on protein concentration. "Definitely from here on, going forward,'' he says, "if we continue to go with anything from China, we will definitely be doing as many checks as we can."

Additional reporting by Lisa Stein