Extraction and Colorimetric Quantification of Uronic Acids of the Pectic Fraction in Fruit and Vegetables

The total pectic content of a selection of fruits and vegetables was studied using a spectrophotometric method developed for the determination of uronic acids in biological fluids. This method was used on pectic extracts obtained from food samples after most of the components that produce interference was removed. The preliminary extraction process varied with the food analyzed. The pectic fraction was quantified using a phenolic reagent (m-hydroxydiphenyl) specific for uronic acid which did not interact with the sugars present in the sample. The validation study showed a recovery rate of 82 ± 3.8 to 95 ± 2.5%, which was considered acceptable for such a complex extractive process. Mean sensitivity was 2.89 mg/ml. Analysis of a standard range of galacturonic acid concentrations (0.0125–0.1 mg/ml) yielded linear results. The intraassay and interassay coefficients of variation were 3.9 to 6.2 and 2.4 to 3.0%, respectively. Use of the method on a variety of fruit and vegetable samples confirmed its effectiveness.