|Cameron, Randall - Randy|
|Chau, Hoa - Rose|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/9/2002
Publication Date: 4/9/2002
Citation: Hotchkiss, A.T., Savary, B.J., Cameron, R.G., Chau, H.K., Brouillette, J.N., Luzio, G.A., Fishman, M.L. 2002. Enzymatic modification of pectin to increase its calcium sensitivity while preserving its molecular weight. Journal of Agricultural and Food Chemistry 50: p.2931-2937. Interpretive Summary: Pectin is a valuable ($5-8/pound) food 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 the residues of fruit juice, sugar beet sugar and sunflower oil processing that are now used for cattle feed (< $1/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 food and industrial chemical markets can be developed. Enzymatic deesterification has the advantage over chemical methods in that pectin's degree of deesterification can be modified without altering its molecular weight which would decrease gel strength. Unfortunately, previous attempts to enzymatically deesterify ypectin did not use pure enzymes so some change in molecular weight was possible. We used pure pectin methyl esterase from orange peel to deesterify pectin. The changes in pectin gel strength produced by this enzyme indicate that it produces blocks of deesterified pectin which will improve its functional properties in food and industrial chemical products. The development of new food and industrial chemical markets for pectin will improve the utilization of domestic pectin reserves.
Technical Abstract: A commercial high methoxy citrus pectin was treated with a purified salt-independent pectin methylesterase (PME) isozyme isolated from Valencia orange peel to prepare a series of deesterified pectins. A series of alkali deesterified pectins was also prepared at pH 10 under conditions permitting Beta-elimination. Analysis of these pectins using high- performance size-exclusion chromatography (HPSEC) with on-line multi-angle laser light-scattering, differential viscometer and refractive index (RI) detectors revealed no reduction in weight average molecular weight (150,000) in the PME-treated pectin series, while a 16% reduction in intrinsic viscosity occurred below a degree of esterification of 47%. In contrast, alkali deesterification rapidly reduced both molecular weight and intrinsic viscosity to less than half of that observed for untreated pectin. PME treatment of a non-calcium sensitive citrus pectin introduced calcium sensitivity with only a 6% reduction in the degree of esterification. Triad blocks of unesterified galacturonic acid were observed in 1H-NMR spectra of this calcium sensitive pectin. These results demonstrate that the orange salt-independent PME isozyme utilizes a blockwise mode of action. This is the first report of production of a calcium sensitive pectin by PME treatment without significant loss of the pectin's molecular weight due to depolymerization.