Removing the Glands From Cottonseed

Catherine Hall Pominski, Leah E. Castillon, Joseph M. Dechary.

Cottonseed differs from other oilseeds in that it contains dark spots, which are scattered throughout the kernel. The spots are actually pigment glands. They contain nearly all the pigments of the seed and have been the cause of many troubles to millers who process cottonseed into oil and meal, the old standby products of the cottonseed industry. The amounts and kinds of pigments in the glands and the number of unbroken glands that remain in the meal after processing determine how highly colored the oil will be and how great the food value of the meal. The glands are the only parts of cottonseed that as yet have no commercial value.

Research on the nature and properties of the glands by Charlotte H. Boatner and others at the Southern Regional Research Laboratory led to the development of a novel method of processing cottonseed. The application of the process on a commercial scale will open the door to new products.

The tiny pigment gland, no larger than a pinpoint, is not the insignificant nonentity its appearance would indicate. Seeds of every species of cotton contain pigment glands. The naked eye sees them merely as black spots. Under the microscope they appear brilliantly and variously colored, from yellow through orange and red to purple. Their size and shape are generally related to one another: Small ones are almost spherical; large ones are more elongated. They are so small that all the glands in a single seed make up 1 to 3 percent of its total weight.

Many years before the Southern Laboratory existed, two of the early investigators who examined cottonseed described some of the properties of the pigment glands. Heinrich von Bretfeld in 1887 and T. F. Hanausek in 1903 described the presence in cottonseed of a water-sensitive membrane, which surrounded a greenish-black opaque secretion. More than 40 years later, Dr. Boatner and her assistants found that the outer structure of the pigment gland is a more or less rigid wall, rather than a membrane. They also learned that the wall is exceedingly strong, so strong, in fact, that it was not broken when a cottonseed kernel was rolled out into a flake a few thousandths of an inch thick by applying thousands of pounds of pressure to the rolls. The wall, they discovered, actually is made up of 5 to 8 irregularly shaped and curved plates, fitted together to give the appearance of a baseball cover. The plates, held together by one of Nature's cements, formed the tiny gland which contained the cottonseed pigments.

The walls will break the instant the glands are placed in water a fascinating thing to watch under the microscope. The material inside a gland becomes cloudy the instant water comes in contact with it, indicating that the water has entered the gland and caused a precipitation of the water-insoluble pigments. Immediately thereafter, the contents of the gland are expelled through ruptures in the walls with a force that resembles jet propulsion. The jetlike streams are usually yellow, but occasionally they are red or purple. The streams consist of finely divided particles, which dance up and down and to and fro, exhibiting what botanists call the Brownian movement.

Organic liquids, such as methanol (wood alcohol), ethanol (grain alcohol), isopropanol, acetone, and dioxane, also rupture the glands, but not in the spectacular manner of water. When water is added to the organic liquids, the speed of rupturing is increased in proportion to the amount added. The hydrocarbons, like hexane (light gasoline) and certain chlorinated hydrocarbons, which will extract the oil from the seed tissue, do not affect the glands or their contents.

DR. BOATNER'S GROUP discovered that the walls of the glands are extremely resistant toward the action of certain solvents and also that they are lighter in weight than the rest of the seed. It occurred to one of her assistants that it should be possible to separate the tiny glands. To do so, they prepared what became known in their laboratory as the "cottonseed cocktail." Very thin cottonseed flakes and a mixture of solvents that would not cause breakage of the walls of the glands were violently agitated in a blender of the kind frequently used to mix fruit juices. The density of the solvent mixture was adjusted to a value between the density of the glands and that of the other seed tissue. When the mixture was allowed to settle in the mixer, the little black glands rose as if by magic to the top, and the yellow meal settled to the bottom. The oil of the seed was dissolved in the solvent.

This method of separating the glands by causing them to float was called the gland-flotation process. The other products, meal and oil, which result from application of this method of processing are actually superior in many ways to those produced by older methods. The third product, the pigment glands, is entirely new.

Prepilot-plant and a pilot-plant operation of this invention provided large enough quantities of separated glands and gland-free meal for studies of their chemical, physical, and physiological properties.

Of the whole pigment gland, 40 to 50 percent by weight is wall, 35 to 50 percent is a yellow pigment called gossypol, and 0.05 to 3 percent is a purple pigment called gossypurpurin. The presence of the two pigments explains the colors, which are caused by variations in the relative amounts of each pigment inside the gland.

Back in 1886, an English chemist named Longmore first isolated the yellow pigment gossypol from cottonseed. Obtaining even a very small quantity of gossypol from cottonseed has always been a time-consuming task. The development of the flotation process made it possible to get large quantities of pigment glands and, from them, equivalently large quantities of gossypol. Three chemists, Leah E. Castillon, Catherine M. Hall, and Dr. Boatner, devised the simple and relatively rapid method, now available to industry, that will separate pure gossypol from cottonseed pigment glands in yields as high as 60 to 70 percent of the total amount present.

ALTHOUGH COTTONSEED MEAL has long been accepted as an excellent feed for cattle, it can be fed in only very limited quantities to other farm animals. For many years the reason for the differences in the amounts of the meal that could be fed animals was thought to be the presence of gossypol. After it was found that all the gossypol and the gossypurpurin of the seed are contained in the pigment glands, the glands were tested to determine their physiological activity in animals. The work was done through the cooperative efforts of scientists at the Southern Laboratory and nutrition experts in the laboratories of several commercial firms and universities.

Dr. Edward Eagle of Swift & Co. added small amounts of pigment glands to diets of rats, mice, guinea pigs, and rabbits. The glands were deadly to all the test animals in relatively small doses, but when he fed gossypol to his experimental animals he found that much larger quantities fed over much longer periods were necessary to kill them.

At the nutrition laboratories of the Ralston-Purina Company, separated pigment glands, added to the basal soybean diet of chickens, caused a definite slowing of growth. The same effect was noted upon feeding cottonseed that had been extracted by an organic solvent such as hexane to remove the oil without materially affecting the glands or their contents.

The pale yellow gland-free meal obtained by the flotation process produced excellent growth in chicks. The experiments make it apparent that the toxic components of raw cottonseed are confined to the pigment glands.

Feeding laying hens cottonseed meal, processed by the older methods, in the past resulted in the development of objectionable color in eggs during cold, storage. No discolored whites and very few dark-colored yolks were found in stored eggs laid by hens fed on the new type of cottonseed meal.

The excellent feed value of the gland-free meal is not entirely the result of being essentially free of pigment glands, but also because it is not heated to high temperatures during processing. That fact has stimulated extensive research on the production of better meals. The present methods, screw pressing and hydraulic pressing, are used in the investigations. The effect of changes in the processing conditions on the quality of meals is now being studied. Industrial cottonseed mills, as well as Government and university nutrition experts, are cooperating in the undertaking.

The oil that is extracted from the seed by use of the gland-flotation process is very light in color and can be refined and bleached by the methods used for ordinary crude cottonseed oils.

So far, we have been talking principally about only one of the pigments in cottonseed. Chemists at the Southern Laboratory found several others in the tiny pigment glands. One is gossypurpurin, the purple one which we have mentioned. Gossyfulvin, an orange pigment, and gossycaerulin, a blue pigment, were also discovered and named by the chemists. Indirect evidence points to the presence of 10 and possibly more pigments in oils and meals prepared by different methods. They have not yet been separated in pure form, and the quantities are so exceedingly small they may defy isolation for a long time.

THE UTILIZATION of gland-free cottonseed flour in markets from which old-process meal has been excluded, mainly for feeding chicks and swine, and as a source of high-quality industrial protein, can result in a larger income for the cotton planter and processor.

Separated pigment glands, an entirely new product, can be the source of further revenue. They represent a source of new raw materials, particularly gossypol, which offers many possibilities for further research. If practical uses can be found for the glands or the pigments, the gland-flotation process makes it possible to produce 90,000 to 100,000 tons of glands and 20,000 to 30,000 tons of gossypol annually from our cottonseed.

CATHERINE HALL POMINSKI is a chemist in the oil and oilseed division of the Southern Regional Research Laboratory in New Orleans. Since 1944, she has been engaged in investigations of the physical, chemical, and physiological properties of the pigments of cottonseed.

LEAH E. CASTILLON is a graduate of Newcomb College, Tulane University, and a native of Louisiana. She has been engaged in research on the pigments of cottonseed since 1945, as a chemist in the protein and carbohydrate division of the Southern Laboratory.

JOSEPH M. DECHARY is a native Louisianian and has been working on the nutritive value of cottonseed meal since his employment as a chemist by the Southern Laboratory in 1948.