Uses for Vegetable Wastes

by J. J. WILLAMAN and R. K. ESKEW

VEGETABLES are important but wasteful. Twenty-odd kinds of plants are commonly grown for vegetables in the United States. In every State they are grown commercially; the highest concentrations are in California, New York, Texas, and Wisconsin; returns from them to growers approach 300 million dollars a year. But not more than 20 to 30 percent of the crop is eaten.

The waste portions 4 million tons of them are mostly leaves. Some wastes are left on the ground to be plowed under; some are fed; some are discarded in dumps; some are a plain nuisance; a tiny fraction is artificially dried for feed. The most conspicuous constituent of the wastes is water about 75 to 90 percent.

One of the tasks assigned to the Eastern Regional Research Laboratory was to find further uses for vegetable crops. We found out soon enough that if any of these widely scattered, widely diverse wastes were to be utilized industrially certain conditions had to be met. The materials must contain some valuable constituents. For most uses they must be dried, partly for preservation, partly to cut down transportation costs. They Must occur abundantly in a restricted area, to minimize hauling to the drier or other processing unit. A succession of wastes must be available, in order to keep a drier occupied for as long a season as possible. Two of the requisites the chemical composition and the preparation of dried material are technical questions, and we have directed our attention mostly to them. The others are questions of economics and have to be answered mainly by the person who is considering the exact location of a plant to use the wastes.

Because leaves are the manufacturing parts of the plant, we would expect them to be high in valuable constituents. And they are: Meal from alfalfa leaves is more nutritious than meal from alfalfa stems; grass leaves are highly nutritious. We therefore looked to leafy wastes as the most promising materials for study and were ultimately rewarded by being able to produce leaf meals of good quality, with high protein, high carotene, fairly high fat, and low crude-fiber contents.

At first, the leaf blades, midribs, stems, pods, and other tissues were separated by hand for chemical analysis. When it became obvious that the leaf blades were the important portion, a special drying technique and mechanical separation were devised for recovering them.

The leaf meals commonly have a protein content of 25 percent or more. Broccoli actually has reached 44 percent, which approaches that of oilseed meals. A few scattered analyses of other leaf meals show 30 percent for celery, 27 for collards, 27 for rhubarb, and 32 for rutabagas.

Carotene, a yellow pigment that becomes vitamin A in the body, is abundant in green leaves, but is low in the less green stems. The carotene content of all these vegetable leaf meals compares favorably with that of alfalfa; in fact, considering the nature of the leaf meal and its other nutritive constituents, a carotene content of 830 International units per gram (500 parts per million in the accompanying chart) compares favorably with a fish-liver oil standardized at 4,000 I. U. And a riboflavin content of 20 parts per million is appreciable in comparison with 25 in skim-milk powder, a product used largely as a source of that vitamin.

Considering all three of these nutrients, the vegetable leaf meals show very good analyses for feed value. As one truck grower put it, "I am wondering if we humans aren't eating the wrong parts of the plants."

There is considerable range in the content of a substance in any one kind of vegetable. Most of the data we have are for vegetables grown along the Middle Atlantic seaboard. Samples from other regions might be different. In fact, the highest protein found in carrot leaves was in samples from the Florida Everglades. Dead leaves accompanying the waste reduce the values. We have noticed year-to-year variations. Within the same year, broccoli has shown a peak in protein and in carotene in August.

The proof of the pudding is in the eating. Do feeding trials confirm the chemical analyses of these leaf meals? They do, within the limits of some experiments with poultry at the Delaware Agricultural Experiment Station and at a commercial poultry farm.

A preliminary investigation on the use of dried vegetable wastes was made by substituting dried pea vine, lima bean vine, turnip, broccoli, and carrot leaf meals for the 8-percent alfalfa leaf meal in a practical all-mash broiler ration. None of the wastes had harmful effects on the birds, growth was best with broccoli and carrot diets, and feed efficiency and pigmentation were best with broccoli and turnip. Furthermore, the chicks liked the new leaf meals better than they did alfalfa.

The carotene in 3 percent of broccoli leaf meal gave as much growth as an equivalent amount of vitamin A in fish-liver oil. The broccoli imparted a deep-yellow color to shanks and skin, giving the birds a good market appearance. Although a level of 1 percent supplied sufficient vitamin A, it had to be supplemented with a little riboflavin for maximum growth.

Pea vines are abundant in several sections of the country and are already collected at the viners in great piles. Because of difficulty in obtaining a true leaf meal from them, their analyzed nutrients are lower than in other wastes, and are about equal to those of alfalfa leaf meal. In a feeding trial with chicks, the pea-vine meal was about equal to alfalfa; it was inferior one year and superior the next.

Spinach, rhubarb, and beet leaves contain appreciable amounts of oxalic acid. This acid is usually frowned on, because it may sequester calcium in feed. In actual trials with chicks, however, at levels at 2.5 to 3.8 percent of the normal basic ration, just as good growth was obtained as with 5-percent alfalfa or pea vines.

Kale and lima bean leaf meals have also been used in chick mashes With complete success.

In laying trials involving about 800 birds, 2.5 percent of broccoli leaf meal alone was substituted for the 5 percent of alfalfa leaf meal and 0.5 percent of fish-liver oil in the controls. Slightly higher egg production was obtained with the broccoli mash over a 3-month period. In hatching experiments, nearly equal hatches were obtained when 2.3 percent of broccoli and 0.5 percent of fish-liver oil were substituted for 5 percent of alfalfa and 1 percent of fish-liver oil.

We can conclude, then, that these leaf meals are satisfactory supplements to chicken feed, whether for growing, laying, or hatching. They have not been tried on other poultry or on other farm animals.