Mustard Seed: Phenolic Composition and Effects on Lipid Oxidation in Oil, Oil-in-Water Emulsion and Oleogel

White mustard (Sinapis alba L.) seeds were investigated for their phenolic profile and antioxidant potential. Sinapic acid was identified in significant quantities, as sinapine, and also as methyl and ethyl sinapate, which are generally less reported in the literature. p-Hydroxybenzoic and sinapic acid were the main phenolic acids in both the free fraction and the fraction released from the soluble bound form, with higher p-hydroxybenzoic acid than sinapic acid. 4-Hydroxy-3-nitrophenylacetic acid and its alkyl esters were also identified. Among the flavonoids, the most abundant were quercetin and epicatechin. In addition to radical-scavenging activities, the mustard seed methanolic extract showed reducing power and chelating activity. On the basis of results of its effect in emulsion, bulk oil and oleogel oxidation assays and the polar nature of the principal antioxidant components, it would be best suitable in bulk oil and oleogel lipid systems, for the prevention of lipid peroxidation.