Chemical Composition and Nutritional Value of Corn Grain

The chemical composition of a corn kernel is, on average, dominated by carbohydrates — roughly 60–72% starch — with 12–14% protein and about 6% fat, plus smaller amounts of sugars, pentosans, fibre and minerals. It is worth noting that the kernels of individual botanical varieties of maize differ not only in shape and structure but also in chemical makeup, so the exact figures shift from one type to another.

What substances make up a corn kernel?

A corn kernel is built mainly from starch, protein, fat and mineral salts, and the proportions vary between botanical groups. The table below shows the content of the most important substances in the kernels of the five most widespread types of maize.

As the table shows, dent and flint maize contain the most starch (79–80%); popping maize is richer in protein than the other types (16.7%); and sweet maize leads in fat (9.4%). Each botanical group therefore has a distinct nutritional profile even though all of them belong to the same species.

How much mineral matter (ash) does maize contain?

In terms of ash content — that is, the amount of mineral salts — these maize varieties differ very little from one another, all falling close to the 1.3–1.7% range seen in the table above. The differences that matter for nutrition lie mainly in starch, protein and fat rather than in the mineral fraction.

If one tries to define the average chemical composition of a corn kernel without reference to its botanical variety, the picture can be summarised quite simply. The kernel of maize contains, above all, a large amount of starch: from 60 to 72%. Protein is present in smaller quantities, only 12–14%, while fat averages about 6%. Sugars make up 1.5 to 3.5% of the corn kernel, and in certain varieties — namely sweet maize — they can reach around 5%. In addition, the kernel holds 6–8% pentosans (carbohydrates with a complex composition), 2–2.5% fibre and 1.5–2% mineral substances.

How does corn compare with wheat and rye?

Compared with wheat and rye, corn stands out for its higher fat content and slightly higher calorie value, while carrying somewhat less protein. It is instructive to set the chemical composition of the corn kernel beside that of these two other widespread cereals.

The comparison below draws on the official "Tables of the Chemical Composition and Nutritional Value of Food Products" published by the Ministry of Health (figures in %).

The figures highlight that maize carries notably more fat — 4.6% against 1.7% in both wheat and rye — which is why 100 grams of corn yields 362 calories, more than wheat (347) or rye (346). Maize, however, is the lowest of the three in protein, at 10% compared with 12% for soft wheat and 11% for rye.

Which vitamins does corn contain?

Corn kernels also supply several vitamins: the B group (including B₁ and B₂), vitamin PP (nicotinic acid) and vitamin E (tocopherol). Yellow varieties of maize are additionally rich in vitamin A, present in the form of carotene — a provitamin A.

The carotene content of yellow maize ranges from 60 to 240 gamma per 1 gram of substance. The role of vitamins in nutrition is well known: present in food, they support the metabolic processes of the body, and their absence brings on a range of serious disorders known as vitamin deficiencies (avitaminoses).

Ripe corn grain has two notable shortcomings. It is entirely lacking in vitamin C, the antiscorbutic vitamin, and it contains only a very small amount of vitamin PP (nicotinic acid). These gaps matter when maize forms the dominant part of a diet.

What do the carbohydrates, fats and proteins of corn do?

The main components of the corn kernel — carbohydrates, fats and proteins — each serve a distinct purpose in nutrition, supplying energy and the building blocks the body needs. Since their general role in food is familiar to most readers, a brief summary is enough here, with particular attention to the protein question taken up separately.

Carbohydrates — which include all sugars as well as starch, pentosans and fibre — are the body's chief source of energy. When oxidised, or, as it is loosely put, "burned", each gram of carbohydrate gives the body 4.1 kcal of heat. Part of the carbohydrate taken in is also stored "in reserve" in the liver and muscles as a special animal starch called glycogen.

The fats of corn were for a long time regarded only as "fuel" — that is, as energy material. Fat is more than twice as calorific as carbohydrate: each gram yields not 4.1 kcal like carbohydrate and protein, but 9.3 kcal. More recently, fats have come to be seen not merely as an energy source but as an important biological part of the diet.

This aspect of corn fat is examined in more detail elsewhere, in the discussion of the kernel's oil — corn oil. The protein of maize is so significant in its own right that it warranted a dedicated article on corn protein.