Sinapic Acid and its Derivatives Increase Oxidative Stability in Different Model Lipid Systems

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Abstract
Sinapic acid and its derivatives syringic acid, syringaldehyde, three sinapoyl esters (ethyl, propyl, butyl sinapates), 4‐vinylsyringol, and sinapine are investigated for anti‐radical activity in relation to different free radical species, reaction environments and model systems, and with special emphasis on lipid peroxidation in different lipid systems: as an emulsion, bulk oil, oleogel and liposome suspension. Syringic acid and sinapic acid show the highest DPPH• and O2•− scavenging activities, whereas for the •OH‐scavenging the highest activities are for ethyl sinapate, propyl sinapate, and sinapine. While sinapic acid esters have the highest activities in the emulsion and liposome suspension, in bulk oil, the more polar sinapic acid, syringic acid, and syringaldehyde show the greatest inhibition of lipid peroxidation. In oleogel‐based system a noted increase in the activity of less polar compounds, especially 4‐vinylsyringol and butyl sinapate is recorded, while the level of inhibition for the more polar sinapic acid, syringic acid, and syringaldehyde remain unchanged, compared to the bulk oil. In oleogel the potential interactions of these less polar compounds with the oil structuring agent might be an additional factor that influences their inhibitory actions.Practical Applications: This study examines the potential for the application of sinapic acid and its derivatives for inhibition of lipid peroxidation, using different lipid systems as models for real food matrices. The study shows how modifications to the naturally occurring compound sinapic acid can affect its activity, and which of these modifications would be appropriate for each lipid system. It is also shown that contrary to the polar paradox, the influence of lipophilic antioxidants on the oxidative stability of oleogel‐based products might be due to their interactions with the oleogelation agents, which will thus further stabilize the oleogels. In addition to their antioxidant actions, this would open new possibilities for the application of lipophilic antioxidants to oil‐based products.While sinapic acid esters [ethyl sinapate (SE), propyl sinapate (SP), butyl sinapate (SB)] have the highest activities in the emulsion and liposome suspension, in bulk oil, the more polar sinapic acid (SA), syringic acid (SY), and syringaldehyde (SYA) show the greatest inhibition of lipid peroxidation. The increase in lipophilicity in sinapic acid by esterification and decarboxylation [4‐vinylsyringol (VS)] results in increased antioxidant activity in oleogel, compared to bulk oil, which is contradictory to polar paradox. This indicates interference in the oil structuring by the more lipophilic compounds.
Funding Information
  • Erasmus Mundus Action 2 Project
  • Slovenian Research Agency (P4-0121)

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