Skip to main content
ARS Home » Research » Publications at this Location » Publication #165624


item Luzio, Gary

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Proceedings
Publication Acceptance Date: 12/27/2004
Publication Date: 12/31/2004
Citation: Luzio, G.A. 2004. Determination of galacturonic acid content of pectin using a microtiter plate assay. Proceedings of Florida State Horticultural Society. 117:416-421.

Interpretive Summary: Pectin is commonly used in the household to make homemade jellies and jams and is found in plant cell walls. Typically pectin produced from citrus peel and knowing the amount of pectin present in the peel is an important parameter for production of this polysaccharide. In this work it was shown that a microplate procedure can be used to perform an assay on pectin. This assay is both safer and faster than previous assays. As many as 96 samples can be assayed simultaneously and the handling of hot sulfuric acid is minimized by the use of the microplate procedure. In addition, the microplate procedure is very rapid which minimizes loss of color from the reaction and minimizes color development caused by other sugars which may be present in the assay.

Technical Abstract: The amount of galacturonic acid residues in samples containing pectin is an important parameter in the quantitative and structural analysis of this complex carbohydrate. This paper describes a method to determine the content of galacturonic acids in samples containing pectin, using a glass microtiter plate and microtiter plate-reading equipment with standard interference filters. The assay is a modification of a procedure involving the hydrolysis of pectin in 80% sulfuric acid at 80°C followed by a coloring step with 3,5 dimethylphenol reagent at room temperature. The previous assay was difficult to apply routinely if large numbers of samples must be analyzed due to color changes that are time dependent, and that involve transferring of strongly acidic solutions to a cuvette prior to reading. The use of microtiter plate assay has several practical advantages such as an accurate estimate of background absorbance by multiple reading of the plates, and many samples can be rapidly assayed in one plate to minimize errors due to fading of the chromophore. This method is particularly advantageous when a large number of pectin samples must be analyzed for their content of galacturonic acid residues.