Free and insoluble-bound phenolics: How does the variation of these compounds affect the antioxidant properties of mustard grains during germination?

[Display omitted] •The best germination conditions for boosting antioxidant in mustard varieties were proposed.•The germination of mustard grains was an excellent option to improve their antioxidant properties.•Soluble and insoluble fractions of phenolics from mustard grains directly affected their antioxidant potential.•Phenolic profile identified by UPLC-MS/MS for each extracted fraction was different. This work aimed to investigate how the variation of free and insoluble-bound phenolics affected the antioxidant properties of mustard grains from two varieties (black - Brassica nigra and white - Sinapsis alba) during different germination parameters. The germination conditions selected for each mustard variety to improve their antioxidant properties were different, as follows: (a) for white mustard – 72 h of germination at 25 °C in the dark and (b) for black mustard – 48 h of germination at 25 °C alternating dark and light periods. At these conditions, increases of 49, 72, 80, 68, 42, 66 and 45% were detected for total phenolic compounds (TPC), total flavonoids, condensed tannins, FRAP, DPPH, ABTS, and ORAC, respectively, for soluble extracts of white mustard compared to the non-germinated white mustard. The soluble extracts from black mustard, in turn, presented increases of 44, 18, 55, 29, 3, 160 and 42% for TPC, total flavonoids, condensed tannins, FRAP, DPPH, ABTS, and ORAC, respectively, compared to the non-germinated sample. Gallic acid, 3,4-di-hydroxybenzoic acid, sinapic acid, ferulic acid, coumaric acid, and rutin were identified by UPLC-MS/MS and were the main compounds detected in mustard extracts. Given the results obtained, germinated mustard grains have the potential for application as a functional and nutraceutical food.