Pectic Content of Plant Materials.

Many plants and plant materials such as wood (2), tea (25), tobacco (15), cotton (16), hops (13), ramie (11), flax (12), grass (6), potato (10), plantain seed (20), celery (9), limes (22), guava (1), bergamnot (23), and root hairs (21), have been shown to contain pectic compounds. Because different methods of extraction and analysis were employed, it is impossible to iiiake comparative studies from these data of the pectic composition, types of pectic materials, and distribution of pectic compounds in these plants. A systematic study, employing uniform treatment of the pectic materials of leaves, cereal grains, apples, and citrus fruits, was conducted by NANJI and NORMAN (18). They determined water-soluble pectin, oxalic-acid-soluble pectin and ammonium-oxalate-soluble pectin. These data were interpreted as representing pectic material present as pectin, pectin in combination with metallic ions, and pectic acid. This interpretation was based on the theory that protopectin is an insoluble calcium, magnesium, or iron salt (19), and that treatment with oxalic acid and ammonium oxalate dissolved the pectin and pectates combined in this manner. More recent studies, however, (3, 4, 14, 17, 24), lead to the conclusion that the pectic molecule is essentially a long-chain, poly-galacturonic molecule combined through intermolecular forces and anhydride structure to form the insolublei protopectin layers of the cell wall and middle lamella. Single treatment with water or acid does not remove any definite pectic compound, but yields a part of a series of pectic substances; continued hydrolysis progressively dissolves the entire protopectin layer. The lack of quantitative data for comparison of the distribution of pectin in the plant phyla has led to the present studv. A large number of plants and plant materials have been included, and in order to obtain comparative data for the concentrations of each pectic fraction present, a system of extraction involving successive stages of hydrolysis was employed. The first stage involves the removal of the water soluble pectin; the second, the easily hydrolyzable protopectini; and the third, the difficultly hydrolyzable protopectin. These analyses have been supplemented by data on gelling power of the pectic material. Extraction and analyses One hundred grams of the material was ground in a sausage mill; 500 ml. of water were added, and the mixture was heated for one hour at 900 C., evaporated water being replaced during the heating. The pulp was then pressed free of the liquid and returned for a second extraction with 500 ml. of water containing 0.155 ml. H,SO4 (pH = 1.5). The pulp was again 809