Synthesis of new phenolic fatty acid esters and their evaluation as lipophilic antioxidants in an oil matrix

The synthesis of new phenolic-based lipophilic antioxidants is described and the structure–activity relationships of an entire family of phenolic fatty acid esters as potential antioxidants have been investigated. Radical-scavenging activity was evaluated by their activity towards a stable free radical, 2,2-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS+) and their efficacy as food antioxidants was evaluated in refined olive oil using the Rancimat method. All the phenolic derivatives acylated with palmitic acid, compounds (1–4 and 17–20) showed better radical-scavenging capacities than did the two control food antioxidants, the commonly-used α-tocopherol (21) and ascorbyl palmitate (22). Moreover, all the di-orthophenolic lipophilic antioxidants prepared (1–12) showed higher induction times in the Rancimat test than did the control antioxidants. It is important to note that fatty acid esters of dihydrocaffeoyl alcohol (3, 6 and 9) exhibited greater antioxidant ability to stabilize olive oil, than did their corresponding hydroxytyrosol fatty acid esters (2, 5 and 8), clearly showing an effect of the length of the alkyl chain attached to the phenyl ring.