Detection of bound phenolic acids: prevention by ascorbic acid and ethylenediaminetetraacetic acid of degradation of phenolic acids during alkaline hydrolysis

The experimental conditions commonly used to detect bound phenolic acids by alkaline hydrolysis result in loss of several phenolic acids, particularly dihydroxy-derivatives (caffeic acid, dihydrocaffeic acid, homogentisic acid). In this study we show that the addition of ascorbic acid, a strong antioxidant, and ethylenediaminetetraacetic acid, a metal chelator, totally prevent the loss of phenolic acids during alkaline hydrolysis. In these conditions, a complete recovery of caffeic acid following hydrolysis of chlorogenic acid (5′-caffeoylquinic acid, an ester of caffeic acid with quinic acid) was found. This procedure has been successfully applied to quantitatively detect bound phenolic acids in coffee brew and apple.