Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 2, 2003
Publication Date: January 1, 2004
Citation: Yoo, S., Fishman, M.L., Savary, B.J., Hotchkiss, A.T. 2003. Monovalent salt induced gelling system of enzymatically deesterified pectin. Journal of Agricultural and Food Chemistry 51:7410-7417. Interpretive Summary: Pectin is a valuable ($5-8/pound) food and industrial gum that is a co-product of the production of juices from oranges, lemons, grapefruits and apples, sugar from sugar beets and oil from sunflower seed. Currently enormous domestic reserves of pectin (900 million pounds) could be produced from orange peel and sugar beet pulp that typically are used for cattle feed (< $0.05/pound). The vast majority of all pectin currently sold in the U.S. is imported. In order to increase demand for the underutilized reserves of domestic pectin, its functional properties as a gelling agent must be modified so that new markets can be developed. Previous attempts to use enzymes to deesterify pectin produced gels in the presence of calcium that were brittle and retained little water. We developed a method to enzymatically deesterify pectin in the presence of salt that produces gels with high gel strength and high water retention properties. These improved gelation properties may lead to the development of new industrial chemical markets for pectin which would improve the utilization of orange peel and sugar beet pulp. Additionally, the concentration of potassium in orange juice may cause pectin aggregation by this new gelation mechanism. Therefore, this new discovery can be applied to prevent cloud loss of fruit juices, and to make calcium more bio-available in calcium-fortified juices.
Technical Abstract: Pectin gels were induced by monovalent salts (0.2M) concurrently with deesterification of high methoxy pectin using a salt-independent orange pectin methylesterase (PME). Constant pH was maintained during deesterification and gelation. If either salt or PME were absent, the pectin did not form a gel. The gel strength was influenced by both pH and species of monovalent cation. At pH 5.0, the pectin gel induced by KCl was significantly stronger than the NaCl-induced gel. In contrast, a much stronger gel was produced in the presence of NaCl as compared to KCl at pH 7.0. LiCl did not induce pectin gelation at either pH. Molecular weights of pectins increased from 1.38 x 10^5 to 2.26 x 10^5 during NaCl-induced gelation, which can be explained by metastable aggregation of the enzymatically-deesterified low methoxy pectin. It was postulated that gelation was induced by a slow deesterification of pectin under conditions that would normally salt out low methoxy pectin.