The phenolic acids isolated from raw and boiled tubers were
primarily chlorogenic and gallic acid and together they constituted
more than 99% of the total phenolic acids content (data not
shown). According to Mattila and Hellström (2007) chlorogenic
acid, caffeic acid and an unidentified acid were the major phenolic
acids in Jerusalem artichoke tubers. Tchoné et al. (2006) also found
salicylic acid, in addition to chlorogenic acid, as the most dominating
phenolics in Jerusalem artichoke tubers. As both chlorogenic
acid and gallic acid can form dark-coloured complexes with iron
due to their o-diphenolic structure, we used the content of these
two phenolic acids as an indicator of the after-cooking darkening
potential of Jerusalem artichoke tubers. Raw tubers had phenolic
acid contents between 38.1 and 57.0 mg/100 g DM in the autumn
and 21.0 and 27.4 mg/100 g DM in the spring (Table 3). There were
no significant differences (p > 0.05) between varieties in contents
of phenolic acids.