Pectic Substances

high-molecular polysaccharides that are formed in all land plants and many species of algae. Especially large quantities of pectic substances are found in fruits, berries, flax stems, and root crops—in particular, the sugar beet. Water-soluble pectic substances are called soluble pectins, and water-insoluble pectic substances protopectins.

Pectic substances are unbranched polygalacturonides, that is, polymers of galacturonic acid in which some of the carboxyl groups are esterified with methanol. Neutral monosaccharides, such as galactose, rhamnose, arabinose, and xylose, are also present in pectic substances. The primary cell walls and the intercellular substance of plants consist mostly of protopectins; soluble pectin are found in the cell sap. Pectic substances contribute to a plant tissue’s turgor, increase a plant’s resistance to drought, and help preserve fruits and vegetables under storage conditions.

As a fruit ripens, pectolytic enzymes alter the quantity and nature of pectic substances, and this produces the characteristic softening. Higher plants, fungi, and bacteria contain the pectolytic enzymes polygalacturonase, pectinesterase, and transeliminase. Many fungi and bacteria synthesize pectolytic enzymes and thus are able to decompose pectic substances. These enzymes also determine the pathogenicity of certain micro-organisms.

Pectic substances that are extracted from plants commercially or in the laboratory are called pectins. An industrially important property of pectins is the ability of their solutions to form firm gels or, in the presence of sugar and acids, to form jellies. Thus, they are used as natural gelling agents in the food industry, for example, for preparing preserves and confectioneries. Pectins are extracted from apple pomace, the rind of citrus fruits, citrons, sugar beet pulp, and the capitula of sunflowers. Preparations that contain pectolytic enzymes are obtained from molds or from plant tissue and are used to clarify wines and juices. Pectolytic enzymes are used to process fiber plants, such as flax and hemp. Pectic substances are used in the treatment of gastric diseases and as preventive agents in certain harmful industrial conditions.