Effect of Boiling, Steaming and Microwaving on the Antioxidant and Antibacterial Properties of Parkia speciosa Seeds

This study investigated the effects of boiling, steaming, and microwaving on the total phenolic content (TPC), cyclic polysulfide content, antioxidant, and antibacterial properties of Parkia speciosa seeds. Ferric reducing antioxidant power (FRAP) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity of the seeds were evaluated. The main antibacterial components of P. speciosa seeds, cyclic polysulfides were characterized using Gas Chromatography-Mass Spectrometry analysis and evaluated using a broth microdilution method against seven gram-positive and five gram-negative bacterial strains. Microwaving displayed the highest decrease in TPC, followed by boiling, while steaming retained most TPC. Thermal treatment did not affect DPPH free radical scavenging activity but significantly reduced the FRAP of the seeds. Uncooked seeds exhibited significant antibacterial activity against the 12 bacterial strains with minimum inhibitory concentration (MIC) values of 5-40 mg/mL. Thermal treatment of the seeds displayed reduced antibacterial activity, a decreased amount of 1,2,4,5-tetrathiane whereas 1,3,5-trithiane and 1,2,5,6-tetrathiocane were detected.