Protein Extraction from Water Spinach (ipomoea Aquatica)

Extractability of protein in water spinach (Ipomoea aquatica Forsk., I. reptans Poir), a possible source of food protein concentrate was examined. Fresh and fresh frozen leaves were extracted by the conventional bufferhomogenate method at room temperature and by a method involving pre-treatment of the leaves with polar and nonpolar solvents. Pre-treatment of leaves with dimethylsulfoxide (DMSO) increased total yield of extractable N slightly and increased extractability of TCA-precipitable protein to 1% of the dry matter (DM). Hot DMSO extracts of fresh water spinach contained protein equivalent to about 8% of the DM. Also, hot DMSO extracted more protein from ace tone-dehydrated leaf meal than from oven-dried meal. Hot (284° F) DMSO extracts, upon dilution with 4 volumes of ethanol, yielded a protein precipitate that dried to a light tan powder. Water spinach (Ipomoea aquatica Forsk., /. reptans Poir) is an aquatic plant found in marshy or wet sandy areas or floating on water in many parts of tropical Asia, Africa, Oceania, and the Americas. It is also known as swamp cabbage (18), ung choi in Hawaii, can cong in the Phillipines, and ung ts'oi in China (17). It is cultivated in south east Asia where it is an important summer vegetable, and constitutes 15% of Hong Kong's vegetable output (5). Morton and Snyder (11) suggested that, as an alternative to sugar cane and other terrestrial crops, water spinach be planted in the Everglades Agricultural Area for use as a vegetable and for preventing organic soil subsidence. We became interested in water spinach as a possible source of food protein concentrate. The edible portion can contain 29% protein on dry matter (DM) basis (18) and may be as suitable a source of food protein as alfalfa leaves (22.3% crude protein) (10). Although alfalfa contains about 7% water-soluble protein (DM), only about 2% of the DM was recovered as a "white" food grade concentrate in pilot-plant studies (6). Water spinach has a lower fiber content than alfalfa (18, 10). Fiber decreases protein ex tractability by lowering the effectiveness of grinding to rup ture cells and release protein (8). It also filters out proteinrich chloroplasts from the liquor. Soluble cytoplasmic proteins constitute about 30% of the total protein in spinach, tobacco, tomato, gherkin, and iSouthern Region, Science and Education Administration, U. S. Department of Agriculture. We thank Dr. G. H. Snyder of the University of Florida for provid ing fresh water spinach, and A. W. Griffin for technical assistance. Mention of a trademark or proprietary product is for identification only and does not constitute a guarantee or warranty of the product by the U. S. Department of Agriculture and does not imply its approval to the exclusion of other products which may also be suitable. 140 cucumber leaves or about 5 to 9% of their DM (14). Particulate proteins are more than twice as abundant as soluble proteins, but cannot be solubilized and extracted unless the lipoprotein and glycoprotein complexes in the leaves are ruptured. Lipid solvents dissociate lipid/protein bonds and are used routinely in the treatment of biological tissue for extraction of enzyme protein (12). Because plant pig ments are soluble in lipid solvents, treatment of water spinach with solvents should remove color as well as in crease the extractability of protein. We report on screening of a variety of organic solvents for increasing extractability of protein from water spinach and on the discovery that one of the solvents is effective for extracting protein. Materials and Methods Fresh water spinach was obtained from the Agricultural Research and Education Center (AREC), Belle Glade, FL. Leaves were washed, air-dried to remove adherent moisture, and frozen for storage. These are referred to as fresh-frozen leaves. Fresh leaves were also harvested from plants grown at our laboratory. Dimethylsulfoxide (DMSO) was obtained from Aldrich Chemical Company, Milwaukee, WI; other chemicals and reagents were from Fisher Scientific Company, Pittsburg, PA. Moisture content was determined on 3.5 oz (100 g) samples of water spinach leaves by drying at 140°F (60°C) in vacuum to constant dry weight. Protein was determined by the biuret method (7) and by Potty's method (13). Amino acids and small peptides were determined by the method of Spies and Chambers (15).