Determination of degree of methylation of food pectins by chromatography


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Correspondence to: Gary A Luzio, USDA, ARS, US Horticultural Research Laboratory, 2001 South Rock Road, Fort Pierce, FL, 34945-3030, USA. E-mail:



In Florida, 90% of citrus is processed into juice, leaving large amounts of peel waste that could be processed into food ingredients such as pectins for other applications. Pectins of low degree of methylation (DM < 50) have important functional properties for use in foods and pharmaceuticals. Thus determination of DM is important, but DM analyses are difficult to perform and assays can have interference due to the presence of salts or neutral sugars.


A chromatography method has been developed for determination of DM of food pectin using alkaline hydrolysis followed by pectin digestion with a commercial pectinase. Analysis was performed by ion exclusion chromatography (IEC) to obtain methanol (MeOH) concentrations and by anion exchange chromatography (AEC) to obtain galacturonic acid (GalA) concentrations. Data were compared with values obtained using other DM analysis procedures. For example, a 55–75 DM pectin assayed as 55.5, 59.6, 60.1 and 57.0 DM by IEC, AEC, colorimetric and conductivity detection methods respectively.


The chromatography procedure described in this paper provides an alternative method for determination of DM of food pectins for accurate and efficient analysis when confronted with limited quantities or large numbers of samples. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.