The effect of pH on the phenolic content and antioxidant properties of three different mustard extracts

Mustard seeds are cultivated worldwide due to their substantial agronomic value of their high protein, oil, and phenolic content. The latter bioactive compounds give mustard seeds various applications in the food and pharmaceutical industries, as antimicrobial, antioxidant, and chemoprotective agents. By modifying the pretreatment and extraction conditions, a significant improvement in the quantity and quality of these crucial compounds was obtained. Based on the electrostatic interactions between the solvents and the extracts, an alternative green extraction procedure was used on three varieties of mustard seeds (Oriental, black, and yellow). Preliminary results demonstrated an interesting trend in which the isoelectric pH value affected the antioxidant activity of the extracts. A number of different antioxidant assays together with total phenolic content (TPC) and total flavonoid content (TFC) were conducted on the three different mustard seeds as affected by different combinations of times and pHs. With the exception of metal ion chelation assay, the other antioxidant methods, including ferric reducing/antioxidant power assay, 2,2-diphenyl-1-picrylhydrazyl free radical-scavenging assay and ABTS^•+ scavenging assay, significantly (p < 0.05) increased with the pretreatment time for all three pH levels studied. Interestingly, the TPC significantly increased (p < 0.05) with the lower pH level treatments. The highest TPC (2040.32 ± 360.12 mg/g dry weight basis) was obtained from yellow mustard seed under neutral treatment. Conversely, TFC showed no significant differences among the different pretreatment time conditions closer to the neutral pH. PRACTICAL APPLICATION: The usage of food-based solvents with the assistance of a home-scale pressurized wet extraction model represents a green technology that can contribute to a wide variety of applications. This method significantly improved the phenolic content, flavonoid content, and antioxidant potential of the mustard extracts, thus making water the most promising extracted solvent.