Differential Effects of Processing Methods on the Antioxidant Activity of Red and Cream Bambara Groundnut Seeds

Background: The red and cream bambara groundnuts (Vigna subterranea (L.) Verdc.) are generally grown in Thailand. Bambara groundnut seeds must be cooked before consumption. However, the differential effects of processing methods on the antioxidant activity of red and cream bambara groundnut seeds remain unknown. Objective: This study aimed to investigate the antioxidant activity affected by the steaming, boiling, and dry heating processes of red and cream bambara groundnut seeds. Methods: Red and cream bambara groundnut seeds were treated with steaming, boiling, and dry heating processes, and the antioxidant compounds, superoxide anion radical scavenging activity (SOSA), and hydroxyl radical scavenging activity were evaluated. Results: Compared to the raw sample of red bambara groundnut seeds, all processing methods decreased total phenolic and tannin content. Only the steaming process caused a significant reduction in total flavonoid content. All processing methods increased SOSA in the sample of red bambara groundnut seeds. Out of all the processes, the boiling process produced the highest SOSA. However, only the steaming process caused an increase in the hydroxyl radical scavenging activity of red bambara groundnut seed samples. For cream bambara groundnut seeds, only the dry heating process significantly reduced total phenolic, tannin, and flavonoid content compared to the raw sample. All processing methods decreased the SOSA in the sample of cream bambara groundnut seeds. Only the steaming process caused a significant increase in hydroxyl radical scavenging activity. Conclusion: All processes caused an increase in SOSA in red bambara groundnut seeds, however, caused the loss of SOSA in cream bambara groundnut seeds. In both red and cream bambara groundnut seeds, steaming was more efficient than raw, boiling, or dry heating for hydroxyl radical scavenging activities.