Vol 117 (2004): Proceedings of the Florida State Horticultural Society
Handling & Processing

Determination of galacturonic acid content of pectin using a microtiter plate assay

Gary A. Luzio
Published December 1, 2004
  • 3,
  • 5 dimethyl phenol,
  • uronic acid,
  • microplate,
  • browning


The amount of galacturonic acid residues in samples containing pectin is an important parameter in the quantitative and structural analysis of this complex polysaccharide. 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 were to be analyzed due to color changes in the assay that are time dependent. In addition the assay involves transferring of strongly acidic solutions to a cuvette prior to reading. The use of a 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 and it minimizes the transfer of strongly acidic solutions.