Synthesis of caffeic and sinapic mono and di-esters and evaluation of their antioxidant activities
2020
Laguna, Oscar | Baréa, Bruno | Durand, Erwann | Villeneuve, Pierre | Dauguet, Sylvie | Lecomte, Jérôme
Greece Sunflower and rapeseed meals, agro-industrial by-products, could be used for the recovery of caffeic and sinapic acids1 respectively, two phenolic compounds known for their bioactive properties (antioxidant, anti-UV, antimicrobial…). The esterification of these phenolic acids with aliphatic alcohols improves their antioxidant activity in heterophasic lipid systems (oil-in-water emulsions, liposomes…) and even in cultured cells. This phenomenon, referred to as the “cut-off effect”, was attributed to a better location and accumulation of the lipophilic phenolic esters at the oil-water interface where lipid oxidation initiates. In this study we synthesized novel mono-esters (R-(CH2n-OH) and di-esters (R-(CH2n-R) of caffeic acid and sinapic acid with aliphatic α,ω-diols (HO-(CH2n-OH) of increasing chain length and we first evaluated their antioxidant activities in a model oil-inwater (O/W) emulsion, as compared to caffeic acid and sinapic acid taken as references. Only a slight (or no) improvement of the antioxidant activity was induced by the mono-esterification of the phenolic acids, highlighting the negative impact of the hydroxyl group at the end of the alkyl chain. Conversely, a clear “cut-off” effect was observed for the di-esters series showing an improvement of the antioxidant capacity until an optimum was reached for the ester containing four carbons between the phenolic units. Thus, we concluded that phenolic acid di-esters could be used as strong antioxidant in O/W emulsions. Finally, all the esters were tested for their antiradical activity in homogeneous medium using the DPPH assay. Unfortunately, none of them showed a better antiradical capacity compared to the corresponding starting phenolic acid.
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