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Corn gluten feed is the by-product of the wet-milling of maize grain for starch (or ethanol) production. Corn gluten feed consists mainl...

Corn gluten feed



Corn gluten feed is the by-product of the wet-milling of maize grain for starch (or ethanol) production. Corn gluten feed consists mainly of maize bran and maize steep liquor (liquid separated after steeping) but may also contain distillers solubles, germ meal, cracked maize screenings, as well as minor quantities of end-products from other microbial fermentations. The chemical composition of corn gluten feed varies hugely, as it depends on the milling process and on the relative proportions of bran, steep liquor and other components. Particularly, the energy and protein content of corn gluten feed are positively correlated to the proportion of steep liquor in the blend.
The wet-milling process of maize is described in the figure above. The process yields 5 main products: maize starch, maize germ oil meal, corn gluten meal, corn gluten feed and maize steep liquor. After cleaning and removal of foreign material, the maize grain is usually steeped in water with sulfur dioxide (SO2) for 24-40 hours at a temperature of 48-52°C. The role of sulfur dioxide is to weaken the glutelin matrix by breaking inter- and intramolecular disulfide bonds. Steeping at 45-55°C favours the development of lactic acid bacteria that produce lactic acid, lowering the pH of the medium and thereby restricting growth of most other organisms. At the end of steeping phase, the maize kernels contain about about 45% water, have released about 6.0-6.5% of their dry substance as solubles into the steepwater and have become sufficiently soft to be pulled apart easily with the fingers. After steeping, the maize kernels are coarsely ground so that the germs are separated from the endosperm and used for oil extraction which yields maize germ oil meal. The remaining steeping water is condensed into a steep liquor. The endosperm undergoes further screenings that separate the fibre from gluten (protein fraction) and starch slurry. Fibre (bran) can be mixed with steep liquor and maize germ oil meal to create corn gluten feed. The fibre-free endosperm is centrifugated in order to separate the starch fraction and the gluten, which have different densities, resulting in almost pure starch (99% starch), and corn gluten meal.

Corn gluten feed is a feed ingredient mostly used in cattle diets as a source of energy and protein. Its economic value depends upon the relative price of whole grain and protein feeds. In the United States, it is usually considered as a source of protein.
Corn gluten feed is usually sold after drying, but maize processors may save on drying cost by selling wet corn gluten feed.

Note: it is important to note that corn gluten feed should not be mistaken for corn gluten meal, which contains about 65% crude protein instead of 22% and is nutritionally completely different.

Nutritional attributes

Corn gluten feed is a major feed ingredient in ruminant diets, particularly for beef and dairy cattle. Wet corn gluten feed contains 40 to 60% DM while the dry product contains about 88% DM. Corn gluten feed is a moderately high source of protein: it contains about 20-25% DM of protein, more than cereal grains and milling by-products but less than corn gluten meal, distillers' grains and most oil meals. Corn gluten feed is much richer in cell wall constituents than maize grain (crude fibre 6-10% DM, NDF 31-49% DM, ADF 8-13% DM and a low lignin content about 1.2% DM) which tends to limit its use in pig and poultry diets. The crude fat content is usually under 4% DM. Corn gluten feed contains relatively high and quite variable amounts of residual starch, from 11% to more than 30% DM. Ash content is also important (about 7% DM).

The composition of corn gluten feed is influenced by the proportion of steep liquor, which contains more energy and protein than the bran. The ratio of steep liquor to bran is generally 1:3 to 2:3 and differences in nutritive value between products containing low or high levels of steep liquor can be important. Corn gluten feed varies in color from yellow-light brown to dark brown, depending on the amount of steep liquor, drying temperature and drying time. Dried corn gluten feed generally darkens with increased drying temperature or time. Extremely dark corn gluten feed with a "burned" smell may be heat damaged and the protein digestibility may be reduced.

Corn gluten feed is low in calcium but has relatively high levels of phosphorus and potassium. The problem of excess sulfur for cattle has been described in Potential constraints.

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