Monday, August 31, 2009

Nutrient Composition of Cereal Grains

Nutrient Composition of Cereal Grains
In composition, grains are structurally similar as seen; however, they vary in their nutrient composition, containing varying amounts of carbohydrate, fat, protein, water, vitamins and minerals.

The main nutrient component of cereal grains is carbohydrate which makes up 79-83% of the dry matter of grain.

It exists predominantly as starch, with fiber especially cellulose and hemicellulose, composing approximately 6% of the grain.

Lipid (fats and oil) makes up approximately 1-7% of a kernel, depending on the grain. For example, wheat rice, corn, rye and barley contain 1-2% lipid, oats contain 4-7%. The lipid is 72-85% unsaturated fatty acids, primarily, oleic acid and linoleic acid.

Protein composes 7-14% of the grain, depending on the grain. Cereals are low in the amino acids tryptophan and methionine, and although potential breeding may produce cereals higher in the amino acid lysine, it remains the limiting amino acid in cereals.

Grain consumption provides half of the protein consumed worldwide. However, in comparison to foods such as milk, meats or eggs, grains do not include all the essential amino acid contained in animal protein.

The protein is of low biological value and therefore, less efficient in supporting body needs.

Combining food sources of protein is common in cultures throughout the world.

The preparation of traditional dishes combines the lower biological value grains with legumes or nuts and seeds to provide the needed amino acids to yield a complete dietary protein.

For example a combination of beans with rice, or beans with cornbread, tofu and vegetables, or tofu and cashews, chickpeas and sesame seed paste (tahini) known as hummus, peanut butter on whole wheat bread and so forth are combinations creating complete proteins.

Vitamins present in cereals are predominantly the B vitamins-thiamin (B1), riboflavin (B2) and niacin (B3). These vitamins may be lost in the milling process and so are added back through the process of enrichment.

Whole grain products contain some fat soluble vitamins in the germ.

Water is present in cereal grains at levels of 10-14% of the grain. Of course soaking and cooking add water to cereal grains, and the grain size expands as additional water is absorbed.

If flour is high in protein content, it absorbs a lot of water compared to low protein flour.

Mineral are naturally present at higher levels in whole grains than in refined grains. Fortification of refined flour with added iron is common.

Zinc, calcium as well as vitamins also may be added at levels beyond not present in the original grain.

Fiber content is determined by different analysis and includes crude fiber (CF) and total dietary fiber (TDF).

These two measurements are not correlated. Crude fiber is composed of cellulose and the non-carbohydrate lignin. TDF includes cellulose and lignin, plus hemicellulose, pectic substances, gums and mucilages.
Nutrient Composition of Cereal Grains
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