Effect of steam processing on the phytochemical profile, allantoin and diosgenin contents, and antioxidant activity of Dioscorea polystachya Turcz.

Processing conditions can significantly influence the retention and bioavailability of bioactive compounds in Dioscorea polystachya.Therefore, this study aims to evaluate the effects of steam-processing temperature, pretreatment conditions (soaking and non-soaking), and tuber tissue forms (whole tubers, peeled tubers, and epidermis) on allantoin content, diosgenin content, and antioxidant activity in D. polystachya tubers.Steam treatment was performed at temperatures ranging from 60°C to 120°C, while antioxidant activity was assessed using the DPPH radical-scavenging assay.Steam processing altered both allantoin and diosgenin contents.Allantoin content peaked at 60°C (10.24 ± 1.54 mg g -1 sample) and decreased at higher temperatures than the dried control (26.00 ± 1.39 mg g -1 sample).Diosgenin content increased at 60°C (0.21 ± 0.11 mg g -1 sample) compared to the dried control (0.14 ± 0.05 mg g -1 sample) and decreased at higher temperatures.The epidermal tissue contained the highest allantoin and diosgenin contents, followed by whole tubers, while peeled tubers showed the lowest contents regardless of soaking treatment.Soaking before processing enhanced the extractability and retention of these compounds, likely due to increased tissue hydration and cell wall softening.Among the processed samples, treatment at 60°C resulted in the highest DPPH radicalscavenging activity (33.00%), exceeding that of the unprocessed tubers (control) but lower than that of the positive control (gallic acid).Additionally, pretreatment conditions and tissue form affected compound distribution.Overall, the findings indicate that steam processing at 60°C, combined with soaking and epidermis retention, enhances the recovery of functional compounds in D. polystachya.