Corn Protein: Amino Acids, Zein, and Its Role in Human Nutrition
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Corn protein is the protein fraction of the maize kernel, made up chiefly of two proteins — zein and glutelin — that together account for most of the grain's protein balance. Before looking at corn protein in detail, it helps to understand what protein is and why it matters to the body.
What role do proteins play in the human body?
Proteins are fundamental to life itself. Protein is part of every living cell, and within these cells lies the very secret of life.
A well-known statement by Friedrich Engels captures this idea: "Life is the mode of existence of protein bodies, the essential element of which is the constant exchange of matter with the external nature surrounding them; and with the cessation of this metabolism, life too ceases, leading to the decomposition of the protein."
In food, proteins act as a plastic, or "building," material, because the body uses them to create tissues — although, when "burned," proteins also release heat. The caloric value of protein, like that of carbohydrates, is 4.1 kcal per gram of substance.
A shortage of protein in the diet causes serious disorders in the human body, because the body holds no reserves of protein: the protein it expends is replenished solely by the food we eat. Not all proteins are equal, however. Different foods — whether animal or plant — contain different proteins, and they vary widely in nutritional worth.
What is corn protein made of?
Corn protein consists mainly of two proteins, zein and glutelin, each making up roughly 40% of the protein balance of the kernel. The proteins of the maize grain deserve a closer look, because the value of any protein substance is determined above all by whether it contains the essential amino acids.
Of the 20 amino acids that build the protein molecule, only 8 are considered essential, because the human body cannot synthesize them. Among these essential amino acids are lysine, tryptophan, and several others, which must be supplied through food.
Zein is classed as an incomplete protein because it contains no lysine. As a result, corn proteins as a whole are inferior to wheat proteins in their lysine content.
According to the American researcher M. B. Jacobs, the lysine content of wheat protein is 1.5 times higher than that of the protein in yellow corn. The other part of corn protein — glutelin — is, by its amino-acid composition, a complete protein.
Why does corn protein not swell in water?
Corn proteins have a distinctive physical property: they do not swell in water. This trait sets them apart from the proteins of many other cereals and directly shapes how maize behaves when processed.
The non-swelling nature of corn protein is a very important factor when assessing the technological properties of corn flour. Because the proteins do not absorb water and expand, corn flour cannot form the elastic gluten network that wheat flour develops — which is why corn flour behaves so differently in baking and other food applications.
