Fig. 26.—Section of Fully Popped Popcorn. × 150.—(Courtesy of Bureau of Chemistry.) The fully expanded starch grains are nearly half as large as the original cells in which they were contained.
SWEET CORN.
This is a variety of maize which develops a high sugar content and is eaten while the starch is yet soft, in other words, in an unripe state. It is a food product of immense importance in the United States, although almost unknown in Europe. The content of sugar varies from 5 to 8 percent in the fresh, soft kernel. The sugar which is present in the kernel rapidly disappears after the husking or removal from the stalk. In order to secure the maximum sweetness the corn should be cooked and eaten as soon as possible after removal from the stalk. Where it is not possible to do this it should be placed in cold storage after removal from the stalk and remain unhusked until it is ready for cooking. Green corn is universally eaten hot. It is usually cooked by boiling in water, although it may also be roasted before the fire. It has a high food value, and the composition of the grains of fresh, soft, green corn is shown in the following table:
Composition of Fresh Green Indian Corn:
| Moisture, | 73.00 | percent |
| Starch, | 13.50 | „ |
| Sugars, | 6.00 | „ |
| Protein, | 5.00 | „ |
| Crude fiber, | 1.20 | „ |
| Ash, | .70 | „ |
| Fat, | .60 | „ |
Maize Proteins.
—The proteins of maize are composed principally of two zeins. The two forms are differentiated by their behavior toward alcohol. The first form constitutes the zein soluble in alcohol and the second the zein insoluble in alcohol. There are two other proteins in maize existing in small quantities which have been named myosin and vitellin, respectively. There is also a third unnamed variety and small quantities of albumin.
Variation in Maize, under Different Climatic Conditions.
—It is possible that most of the varieties and subvarieties of maize are simply the existing standard varieties modified by changing environments. There are certain conditions of climate, soil, and distribution of rainfall which tend to produce a large, starchy, soft grain, while other conditions tend to produce a small, hard grain richer in protein. The variations of importance are those of the carbohydrates and the protein, which are complementary, since as the protein rises the carbohydrates fall in relative proportion. There is also a marked variation in the carbohydrates, due to variety and climatic conditions combined. It is, for instance, the increase of the sugar at the expense of the starch that produces the body known as sweet maize eaten in the green state, as already described. Even in the sweet variety the relative proportion of sugar varies in different localities and under different conditions of growth.