Evaluation of Various Methods for Measurement of Pectin Content in Jam

Abstract

Suitability, precision, and accuracy of 3 colorimetric methods to measure pectin content in fruit jams are examined. The methods resolve non-uronide interferences in different ways: (1) with 3,5-dimethylphenol colorimetric reagent, and absorbance differences measured at 450 and 400 nm; (2) with m-hydroxydiphenyl colorimetric reagent, and numeric correction of sample blank to compensate for interferences; and (3) with m-hydroxydiphenyl colorimetric reagent and removal of interferences by purification of sample pectins. The 3,5-dimethylphenol method is not suitable when fructose is present. Precision and accuracy of the second method are not satisfactory because sugar/pectin ratio in jam samples is very high. The third method is recommended because the precision (0.9% < CV < 6.4%) is good and recovery is nearly 100%.