Figure 1.
Chemical structure of p-hydroxybenzoic acid (1); caffeic acid (2); protocatechuic acid (3); gentisic acid (4); vanillic acid (5); ferulic acid (6).
Chemical structure of p-hydroxybenzoic acid (1); caffeic acid (2); protocatechuic acid (3); gentisic acid (4); vanillic acid (5); ferulic acid (6).