Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 2007
Publication Date: March 20, 2008
Citation: Luzio, G.A., Cameron, R.G. 2007. Rheological investigation of pectin deesterified using salt-independent pectin methylesterase from citrus. Proceedings of Florida State Horticultural Society. 120:304-309. Interpretive Summary: Converting citrus peel byproducts to useful materials is of commercial importance to the citrus industry. One of the major components of citrus peel is pectin and so conversion to a useful product largely relies on converting the pectin component to something that has utility. Pectin is a water soluble polysaccharide and polysaccharides are generally sold based on rheological properties such as viscosity or other properties such as suspension. Suspension aids, a target application, can be subjected to intermittent shearing forces and studying the effects of shearing is of importance. This research examines in greater detail the suspension properties of pectin using a "gel-in-place" procedure, where one can examine suspension before and after shearing the sample. The optimum level of calcium ion and pectin concentration required for forming the suspension aid was determined using this new procedure.
Technical Abstract: During deesterification, the ester groups on the pectin from citrus peel byproducts can be removed in a random or block wise (sequential) manner. Pectins containing these blocks of unesterified groups on the chain are highly reactive to divalent cations such as calcium ion. In solution, in the presence of calcium ions, pectin treatment by plant pectin esterases can exhibit unique rheological properties. One such property is that they can produce solutions that have pseudoplastic properties that are needed for suspension aids. A non-calcium sensitive pectin with a 94 % degree of methylation was demethylated at pH 4.5 to a value of 55 % degree of methylation using monocomponent citrus salt-independent pectin methylesterase (PME). Rheology measurements on this pectin indicated that to reach a maximum value storage modulus G', a cure time of 20 hours is needed. At an angular frequency of 0.01 rad/sec the G', G" (loss modulus) and tan(') (ratio of loss to storage modulus) values were 9.69 Pa, 0.247 Pa and 0.0255 respectively. These data indicate that the modulus is mostly comprised of an elastic component which is important for suspension applications. A maximum value of storage modulus was observed at mole ratios (calcium ion to free unesterified carboxyl groups) of 1.0 and 1.2 where the G values were 34.5 and 52.1 Pa, respectively.