What the Hell Is Corn Glutten Meal?

What the hell is corn gluten meal, a reader asks. She has seen that it was the #2 ingredient in Purina Pro Plan, the dog food that the late four-time Iditarod winner Susan Butcher fed her dogs.

Ah, corn gluten. Sends a shiver down the spine, doesn't it? I mean look at those two words, sitting side by side.

Corn. "Everyone" knows corn is crap, and never mind if it a key ingredient in every sled dog diet, and never mind if this food has been tested to the outer edge, and proven to be a fine food for dogs, and that there is not one longitudinal peer-reviewed feed trial that says otherwise.

And then there is the word "gluten," with its echo of Chinese toxic dog food.

Wasn't it rice gluten that killed all those dogs? No? Well, no matter. Gluten is bad anyway. Pretty sure about that!

And to prove it, they guickly Google and come up with this little gem: that corn gluten meal can be used as a "natural" herbicide on lawns. An herbicide. They run screaming into the woods. Except that it's not an herbicide -- it's a pre-emergent, and it works by preventing sprouting seeds from developing side roots, which may make young plants susceptible to dehydration if the soil gets dry. For this stuff to work at all, you have to put down 20 pounds of it on 1,000 square feet, and it's not cheap. And it's also not toxic. In fact, it is so non-toxic, that the EPA has made it exempt from all registration requirements -- the same as water.

OK, but why is it being used in dog food?

Simple: because it has been shown to be an effective protein ingredient when paired with other nutriets. As Greg Aldrich, PhD notes on the Pet Food Industry web site:

Why is corn gluten meal used in petfoods? Most of the available CGM [corn gluten meal] contains 60% protein. Thus, it serves a purpose as an economical high-protein ingredient. On a cost-per-unit protein basis, CGM costs about 10% less than petfood-grade poultry by-product meal, but about 20% more than soybean meal. It is a reasonable source of methionine, but low in lysine and arginine. Because of this, CGM is typically paired or complemented with another protein source. Additionally, when compared to other proteins, CGM has a low level of ash.

OK, but I still want to see chicken as the primary ingredient in my dog food.

Fine. Go for it. Your dog will be fine with lots of chicken. But, as Aldrich notes, putting chicken first in ingredient packaging is mostly a gimmick, not sound science:

Chicken as the first ingredient on the ingredient panel of a dry extruded kibble has become more commonplace in the past several years. Why chicken? It is likely because of its popularity and ready supply rather than anything nutritionally unique or special about chicken. Beef, lamb, fish and other meats could be interchanged in this discussion just as easily.

The bigger issue is whether formulating a dry petfood to make a meat the first ingredient on the panel is only a marketing ploy or if it truly imparts some enhancement to nutrition and quality. The cynic will profess that it's all about marketing.

Of course, there is some real truth to the notion that the consumer is going to perceive that a food that is "made with real meat" or has "chicken as the first ingredient" is a higher quality product. And as our marketing brethren are eager to remind us, in the market perception is reality.

Aldrich goes on:

It might not seem intuitive, but to begin answering this question we need to determine exactly what constitutes chicken. The best place to look is the Association of American Feed Control Officials (AAFCO) manual wherein chicken, or rather poultry, is defined as "the clean combination of flesh and skin with or without accompanying bone, derived from the parts of whole carcasses of poultry or a combination thereof, exclusive of feathers, heads, feet and entrails."

Though one might deduce that chicken meal and chicken by-product meal, since they are derived from chicken, would count toward "chicken" as the first ingredient, according to this definition and the labeling rules they don't. It's got to be the real un-rendered chicken.

However, that doesn't mean that it is the pieces and parts that you find in the grocery store. Purchasing chicken for petfood applications occurs primarily in the same supply chain as that of "hot dog or nugget meats."

This chicken is sometimes derived from hand trimming, but more frequently from mechanical separation operations in which the bones have been mechanically removed from the lean. This latter procedure also removes the soft material from the marrow of the bone, which can be high in fat.

The resulting chicken is then either chilled or frozen into blocks. Use in petfood requires that it be brought to a temperature just below freezing, but in a state that can be pumped, a condition that often requires the use of steam.

From the definition, one might think that chicken is all muscle and/or meat. The real ingredient, though, comes with a great deal of water, fat and some incidental bone.

There is also no regulation on the nutrient composition of this chicken, so depending on the materials being deboned and the amount of steam it takes to pump the material, it can vary widely. It is often in the range of 65-70% moisture, with protein around 12-15%, however, and a minimum fat around 10% (though the level of fat can be higher).

How much chicken is in a dog food where the primary listed ingredient is chicken?

Not as much as you think!

So, how much chicken might it actually take to reach the top [ingredient listing on the label]? In general, chicken must occupy around 15% of the formula to go ahead of the other ingredients. From a formulation standpoint this isn't too big an issue, though it does require that the other ingredients compensate accordingly; namely, that the number (but not the content) of protein meals and grains are increased.

The bigger challenge is in the processing. The trick is to manage the elevated moisture and fat from fresh chicken in the conditioning cylinder or extruder so to achieve uniform mixing and cooking. It is only in the last 15-20 years that engineering of extruders and facilities, advances in computerized process controls and improvements in sanitation and meat handling equipment have been able to reach these levels.

One might assume that having this much chicken in the formula would contribute a substantial amount of protein to the diet. However, in most instances chicken adds less than 10% of the dietary protein.

Surprisingly, it may contribute more than 15% of the dietary fat. While this lower protein contribution might seem disappointing, the abundance of fat may help explain why high chicken formulas are more palatable for both dogs and cats.

In short, chicken is fine in dog food, and it may increase palatibility or digestabiltiy, but it's on the margin not the main.

And what about potatoes in dog food -- the newest dog food fad? Adrich writes:

Potato protein is an ingredient just emerging in the petfood and feed market. This ingredient has an opportunity for application in ultra-high protein products as an alternative to rice protein or corn gluten meal especially in elimination diets. Information on its nutrient availability in dogs or cats is limited; but, it's probably only a matter of time before this is rectified.... in a study with dogs, potato flour was reported to have a similar starch digestibility (>99%), and resulted in similar stool scores as cereal grains, although other nutrients (e.g., protein) were slightly less digestible (Murray, et al., 1999).

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