Contactless Conductivity: An HPLC Method to Analyze Degree of Methylation of Pectin

Gary A. Luzio, Randall Cameron


After removal of soluble sugars and other compounds by washing, citrus peel is largely composed of pectin, cellulose, and hemicelluloses. One of the major components, pectin can be modified using pectinesterases, which reduce the degree of methylation (DM). Low DM pectins have great utility in the food industry and other applications. They have been shown to have calcium sensitivity, which is an important functional property of pectins for use in applications which require suspension, metal ion binding or water absorption. Thus, an estimate of DM is an important parameter to determine but most DM analyses are difficult to perform. A new method has been developed based on contactless conductivity. The conductivity, as measured by a contactless conductivity meter, increases with decreasing DM, with values ranging from 94.0 to zero when pectins are analyzed on size exclusion chromatography columns (SEC) with concentration of pectin measured with interferometric refractive index detector (RI). Data fit to a linear equation, of DM to conductivity detector response, yields y = –5.96 × 10–3x + 0.592 with an r2 value of 0.998. These results demonstrate that DM and molecular weight can be measured simultaneously on SEC using contactless conductivity.


polysaccharide, homogalacturonan, degree of esterification, pectinesterase, pectin methylesterase

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