A comparative study on the phenolic acids identified and quantified in dry beans using HPLC as affected by different extraction and hydrolysis methods

A high performance liquid chromatography procedure was used to assess the phenolic acid content in three different varieties of dry beans (Phaseolus vulgaris L.) grown in Canada. The majority of phenolic acids were extracted from the base hydrolysed fraction of the sequential hydrolysis regime. There was a protective effect of ascorbic acid (AA) and ethylenediaminetetraacetic acid (EDTA) when added to the 10 N NaOH hydrolysis step. The mild direct base hydrolysis (2 N NaOH) with and without AA and EDTA protection resulted in a measured total phenolic acid content that was lower than the total phenolic acid content measured for the more aggressive base hydrolysis (10 N NaOH) with protection, yet were comparable to the values obtained for the aggressive base hydrolysis without AA and EDTA protection. Sequential acid hydrolysis did yield a significant amount of compounds that exhibited the same retention times as gallic and protocatechuic acid, however, the UV spectra and masses of the molecular ions present in the peaks of these compounds did not correspond with masses of authentic standards. Thus, the majority of phenolic acids were detected in the base hydrolysed fraction when AA and EDTA were added to prevent degradation of phenolic acids. Acid hydrolysis did release compounds present in beans that were not obtained from base hydrolysis. This work shows that extraction and hydrolysis procedure has a substantial effect on the detection of phenolic acids present in beans.