The chemical modification of anthocyanins (water-soluble pigments) into more lipophilic compounds is very important to expand their application in the food, medical and cosmetic industries. In this work, the synthesis of a pure malvidin-3-glucoside-oleic acid ester derivative was achieved by enzymatic catalysis. This approach allowed us to synthesize a novel compound, malvidin-3-O-(6''-oleoyl)glucoside (Mv3glc-OA), which was structurally characterized by mass spectrometry and for the first time by NMR spectroscopy. The enzymatic reaction revealed to be regioselective giving only one ester product. Antioxidant features of the malvidin-3-glucoside lipophilic derivative by means of DPPH, FRAP and lipid peroxidation assays were assessed, which confirmed that the structural modification of the genuine malvidin-3-glucoside into a more lipophilic compound did not compromise its antioxidant potential and protected more effectively a lipidic substrate from oxidation, which is an important insight for future technological applications.
This work describes the lipophilization reactions of malvidin 3-glucoside with different saturated fatty acid chain lengths using an enzymatic synthesis and the study of their physical-chemical and antioxidant properties. The lipophilic anthocyanins were obtained with satisfactory yields (22-40%) after column chromatography purifications, and they revealed the same appealing chromatic features of the parent anthocyanin. All of the compounds were characterized by mass spectrometry, confirming the regioselective acylation on the glucose moiety. The octanol-water partition coefficients and the hydrophobicity index of the different derivatives were determined, confirming a lipophilicity increase concomitant with the fatty acid chain length. The antioxidant profile was also evaluated by using two in vitro methods (β-carotene-lineolate method and oxygen consumption assay). Overall, a maximum of antioxidant activity was achieved when malvidin 3-glucoside was conjugated with caprylic acid (C8). Altogether, the results obtained provide a good perspective for the technological application of these functionalized anthocyanins in the cosmetics and food industries.
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