By Brent Mayabb, DVM

Printable Version

Corn has become a lightning rod for controversy in today's pet foods. We receive many calls about it, few of which are positive. Its detractors claim that it is contrary to a pet's natural eating habits, is a cheap filler material, and is not very digestible. Some of these misconceptions are due to lack of understanding of the different nutritional aspects of corn. Whole corn and processed corn (corn gluten meal, ground corn, etc.) are worlds apart in terms of usable nutrition. Gluten is defined by AAFCO as the tough, viscid nitrogenous substance remaining when the grain is washed to remove the starch. In other words, it is the protein-containing portion of the corn. Meal is a dried form of gluten.

Here is a simple diagram of a corn kernel:

This diagram breaks down a kernel into its basic components. Starting from the inside and working out, there is the germ, the gluten, the starch, and the hull. Let's look at each one, and the process by which we get them.

The Germ

AAFCO defines the germ as the embryo found in seeds and frequently separated from the bran and starch during milling. The germ contains 85% of oil found in corn. When corn first arrives for processing, it is first inspected and cleaned twice. Next it is "steeped," or placed in a stainless steel tank with water for 30 to 40 hours. Over this time, the kernels will double in size and moisture content will triple as the corn absorbs water! The water actually helps break the gluten bonds from the germ. After steeping, the corn and water undergoes a course grinding to break the germ free. The mixture then passes into cyclone separators. The germ has a lower density, so it separates out of the slurry. After separation, the germs are washed repeatedly to remove any remnants of starch or gluten. Oil is then extracted from the germ and refined for use as corn oil. Corn oil has one of the highest amounts of linoleic acid of any oil.

The Fiber

After the germ is separated out, the slurry is then subjected to a finer grind. This grinding allows the fiber to be released from the gluten and starch. The fiber and the gluten/starch mixture (remember, it hasn't been separated into its two components yet) pass over screens which catch the fiber, but allow the gluten/starch suspension to pass through. The fiber is then slurried and screened again to reclaim any residual starch or gluten. It can then be used for fiber. We have already been able to produce both fat and fiber from corn, and we still have half of the processing to go!

The Gluten

The remaining portions of corn are then transferred to a starch separator. Again, the constituent parts have different densities, with gluten being less dense than starch. The mixture is centrifuged, and gluten is separated out. At this stage, it is still referred to as "wet" gluten. The gluten is then dried to yield corn gluten meal. The advantages of corn gluten meal are high digestibility (very similar to chicken meal) and high biologic value protein. But wait, there's more…

The Starch

The starch, or main carbohydrate portion of the corn that remains, is washed 8 to 14 times to remove any residual protein. Purity can reach 99.5%. The starch that remains can be sold as unmodified starch, modified into specialty starches, or converted into corn syrup or dextrose.

From a single source we have been able to produce fat, fiber, protein, and carbohydrate.