Cereal grains are major food and feed source. The top three stable food grains –rice, corn and wheat – represent over 50% of the human food source.
Nutrition composition of cereal grain may vary from one region or year to the next because of differences on plant genetics or environment.
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 nutritional value of the grains is determined by the nutrient amount and composition in the grains that accumulate during grain filling and by the bioavailability of micronutrients.
Carbohydrate
The main nutrient component of cereal grains is carbohydrate which makes up 79-83% of the dry matter of grain.
Cereals contain small amounts of free sugars of the order of 1-2% although this will rise if the grain has been allowed to germinated, e.g. in the preparation of malted cereals.
It exists predominantly as starch, with fiber especially cellulose and hemicellulose, composing approximately 6% of the grain.
Lipid
Lipids are relatively minor constituents in cereal grains. 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
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.
The protein is of low biological value and therefore, less efficient in supporting body needs.
Protein in cereal grains can be divided into two broad groups based on their biological functions: biologically active enzymes and biologically inactive storage proteins.
The storage proteins make up most (up to 80%) of the total proteins.
Vitamins
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. When considered as a whole, cereals are naturally low in lipids therefore, they tend to be low in the fat soluble vitamin A, which is present as the precursor carotenoids and vitamin D, E and K.
Water
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
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
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.
What are nutrient compositions in cereal grains?
