New Uses for Waxy-Cereal Starches

John H. Martin, Merle T. Jenkins.

Waxy starch exists in the endosperm of the grains of some varieties of corn, sorghum, rice, millet, barley, and Job's tears. The term "waxy" refers to the waxlike appearance of the endosperm of the grain when it is cut or broken; it does not indicate the presence of true wax.

In the Orient, waxy grains are called glutinous; it is because of the gluelike character of the cooked or the wetted grain, flour, or starch. Glutinous varieties of rice and also millet have been known in China for many centuries, and glutinous sorghum has been grown there for at least 300 years. Many varieties of waxy rice, millet, and sorghum are grown in China and other Eastern countries. A few waxy rites have been grown in the United States at times to supply special holiday delicacies to Oriental people living here. The chromosomes in the reproductive cells of corn occasionally undergo sudden changes and give rise to waxy grain.

It remained, however, for the Chinese to discover this new type in a crop that originated in the Americas. The existence of waxy corn (or maize) became known in 1908 when a missionary in China, the Reverend J. M. W. Farnham, sent a sample to the United States Department of Agriculture.

Amber waxy sorghum from China reached the United States about 1854, and that variety or selections from it have been grown here since that time.

Its waxy character was unknown, however, until about 1933, when J. C. Stephens discovered that several other American varieties also were waxy.

From 1944 to 1947, 20,000 to 40,000 acres of waxy corn and sorghum were grown and the grain processed in the United States each year. About 32,000 acres of waxy corn and 5,000 acres of waxy sorghum were grown in 1949.

Waxy-cereal starch produces pastes with higher viscosity and less rigidity than does ordinary cornstarch. Those characteristics make it adaptable to many special industrial uses. The properties of waxy starch resemble those of tapioca starch. We are all familiar with the difference between soft tapioca pudding and stiff cornstarch pudding. Waxy and ordinary starch also differ in their molecular structure.

WAXY STARCH is entirely amylopectin, a type in which the molecules are arranged with many branches. Ordinary starch is a mixture of the amylopectin (71 to 72 percent) and amylose (28 to 29 percent) types. The amylose molecules are arranged in straight unbranched chains. Tapioca starch is about 80 percent amylopectin and 20 percent amylose.

One of the distinctive characters of waxy starch and grains is that they stain red when they are treated with iodine. Ordinary starch stains blue. The difference was discovered in France by A. Gris, in 1860. In 1921, F. R. Parnell, an Englishman working in India, discovered that the pollen of waxy cereals also stains red rather than blue when treated with iodine. Starch in the stems, leaves, and seed coats of waxy cereals gives a blue reaction to iodine, which indicates that the waxy type of starch is formed only in the endosperm and in the pollen. Apparently the factors of heredity in waxy barley, and at least one waxy gene in corn, do not effect complete conversion to waxy starch, because the starch of the mature grain contains 2 to 3 percent of amylose.

THE FIRST ATTEMPT to promote industrial use of waxy grain in the United States was made by R. E. Karper, of the Texas Agricultural Experiment Station. In the early 1930's he crossed the Batad variety of waxy sorghum, introduced from Java, with a domestic kafir variety. From that cross he developed a new waxy variety otherwise like the kafir parent. When the grain supply had been increased to about a ton, he offered it to several processors with the suggestion that it might have special uses. Karper then had visions of new types of baby foods, health foods, or desserts. But no processor could be interested in undertaking the development of products from this strange grain, and so the waxy kafir was used in a hog-feeding experiment. The hogs thrived as well as but no better than did those consuming ordinary kafir.

Interest was revived after 1936 with the discovery of the similarity between waxy starch and tapioca starch. The discovery was made at the Iowa Agricultural Experiment Station by R. M. Hixon, after separating the starch from waxy corn and sorghum supplied by the writers. In 1938, F. H. Thurber, of the Department of Agriculture, made some limited tests of starch which he had separated from waxy and non-waxy sorghums. Chemists at the Kansas and Nebraska Agricultural Experiment Stations started experiments shortly thereafter.

The war cut off our supplies of tapioca flour from the Netherlands Indies, which had furnished about 97 percent of the 300 million to 400 million pounds we imported annually. The emergency focused attention on waxy grains. Representatives of the starch industries began experimenting with the waxy starches for various uses and also with commercial methods for separating the starch from waxy grains.

For several years, work had advanced toward the development of a waxy hybrid corn similar to the non-waxy hybrid, Iowa 939. Each of the inbred lines used in producing that hybrid had been crossed with a waxy corn. Waxy progenies from the crosses were backcrossed repeatedly upon the original inbred lines until the waxy counterparts were recovered. The first test of the new waxy hybrid ( Iowax 1), in 1939, indicated that it yielded only slightly less than did the ordinary hybrid, Iowa 939. Waxy kernels frequently weigh 3 to 5 percent less than nonwaxy kernels, with a corresponding reduction in yield. Unfortunately, in the fall of 1941 less than 2 bushels of Iowax 1 seed was available. Only 335 and 3,800 kernels, respectively, of the two single crosses and limited quantities of seed of the four inbred parental lines needed to produce the hybrid were on hand at that time. The seed supply was increased in large greenhouses at Beltsville, Md., in the winter of 1941-42, and in the field at Ames, Iowa, during the following summer. In 1942, 326 acres of the second-generation hybrid of Iowax 1 was grown, harvested, and processed. That was the beginning of the waxy-corn industry. The growing of such lower-yielding second-generation hybrid corn was merely a temporary expedient. By 1944, some 10,000 acres of the first-generation hybrid was grown; since 1946, about 20,000 acres of waxy corn has been grown annually. An open-pollinated variety of waxy corn developed at the Nebraska Agricultural Experiment Station was grown to some extent for a time.

Breeding operations to convert additional inbred lines of corn to the waxy condition were expanded immediately with the development of interest in the commercial production of waxy corn. Hybrids involving the additional lines were released as rapidly as they became available. As a result, there have been rapid shifts in acreage to the improved hybrids. Iowax 2 was released in 1945, and by 1947 it comprised the bulk of the crop. That hybrid now has been largely replaced by Iowax 4 and Iowax 5. Small acreages of the waxy counter-Parts of U. S. 13 and Kansas 2275, a white hybrid, were grown in 1948. The acreage of waxy U. S. 13 was expanded in 1949. Waxy hybrids developed by a commercial hybrid-corn company also have been grown on a limited acreage.