Chemistry and uses of pectin--a review.

Pectin is an important polysaccharide with applications in foods, pharmaceuticals, and a number of other industries. Its importance in the food sector lies in its ability to form gel in the presence of Ca2+ ions or a solute at low pH. Although the exact mechanism of gel formation is not clear, significant progress has been made in this direction. Depending on the pectin, coordinate bonding with Ca2+ ions or hydrogen bonding and hydrophobic interactions are involved in gel formation. In low-methoxyl pectin, gelation results from ionic linkage via calcium bridges between two carboxyl groups belonging to two different chains in close contact with each other. In high-methoxyl pectin, the cross-linking of pectin molecules involves a combination of hydrogen bonds and hydrophobic interactions between the molecules. A number of factors--pH, presence of other solutes, molecular size, degree of methoxylation, number and arrangement of side chains, and charge density on the molecule--influence the gelation of pectin. In the food industry, pectin is used in jams, jellies, frozen foods, and more recently in low-calorie foods as a fat and/or sugar replacer. In the pharmaceutical industry, it is used to reduce blood cholesterol levels and gastrointestinal disorders. Other applications of pectin include use in edible films, paper substitute, foams and plasticizers, etc. In addition to pectolytic degradation, pectins are susceptible to heat degradation during processing, and the degradation is influenced by the nature of the ions and salts present in the system. Although present in the cell walls of most plants apple pomace and orange peel are the two major sources of commercial pectin due to the poor gelling behavior of pectin from other sources. This paper briefly describes the structure, chemistry of gelation, interactions, and industrial applications soft pectin.