Mustard seeds germination to increase their antioxidant properties: is it a good option?

Germination is a process that promotes the accumulation of several bioactive compounds and offers new opportunities to improve nutritional quality and functional potential of seeds. White mustard (Sinapsis alba) was the specie chosen to analyze the effects of germination on the content of phenolic compounds and antioxidant properties. The germination process was performed under the following conditions: incubation time of 72 h, temperature of 25°C in the dark. The samples were freeze-dried, defatted and frozen at -18°C. The soluble fraction from mustard (SFM) was obtained using as solvent a mixture of acetone and water in equal proportions, incubation time of 20 minutes at 150 rpm in a rotatory shaker; this process was repeated three times. The insoluble fraction from mustard (IFM) was obtained from the solid residue produced after removal of the SFM with basic/acid hydrolysis and ethyl acetate extraction. The extracts contained the soluble and insoluble fractions from germinated and non-germinated mustard seeds were used to determine the content of total phenolic compounds (TPC), flavonoids and condensed tannins. The antioxidant properties were investigated using the following methods: ABTS- and DPPH-radical scavenging activities, the Oxygen Radical Absorbance Capacity (ORAC) and the Ferric Reducing Antioxidant Potential (FRAP). Comparing the extracts obtained from germinated and non-germinated samples, for the SFM, it was observed increases of: 49% in TPC (ranging from 23.05 to 34.32 mg of Gallic Acid Equivalent per gram of sample – mg GAE/g), 73% in flavonoids (ranging from 6.04 to 10.42 mg of Catechin Equivalents per gram of sample – mg CE/g), 79% in condensed tannins (ranging from 1.16 to 2.08 mg CE/g). For antioxidant activities, after germination, the values increased in 68% (ranging from 128.08 to 215.25 micromol of Trolox Equivalents per g of sample - µmol TE/g), 42% (ranging from 49.92 to 71.16 µmol TE/g), 66% (ranging from 180.95 to 300.83 µmol TE/g) and 45% (ranging from 823.31 to 1191.43 µmol TE/g) to FRAP, DPPH, ABTS and ORAC methods, respectively. Similar results were observed for the extracts obtained from IFM, in which the phenolic compounds are linked with macromolecules for cell wall formation, demonstrating that synthesis and release of these compounds can occur simultaneously, elucidating a continuous, complex and dynamic process that is peculiar for each seed. After germination, TPC for IFM increased 35% (ranging from 2.96 to 4.00 mg GAE/g); flavonoids showed a decrease of 11% (ranging from 0.65 to 0.58 mg CE/g) indicating a transformation of flavonoids or maybe the link for cell wall formation. Condensed tannins increased 172% (ranging from 0.94 to 2.56 mg CE/g). All results for antioxidant activities increased, as follows: 16% (ranging from 21.00 to 24.29 µmol TE/g), 44% (ranging from 10.13 to 14.59 µmol TE/g), 119% (ranging from 26.72 to 58.44 µmol TE/g) and 136% (ranging from 60.96 to 143.69 µmol TE/g) for FRAP, DPPH, ABTS and ORAC methods, respectively. The results obtained in our study showed clearly that germination process is a good option to change the biological properties of mustard seeds, allowing the consumption of a product with better antioxidant properties.