Effects of nine-steam-nine-bask processing on the bioactive compounds content, bioaccessibility, and antioxidant capacity of Polygonatum cyrtonema Hua

The traditional ‘nine-steam-nine-bask’ method of Polygonatum cyrtonema Hua (PCH) has been controversial due to nine-cycle requirement. This study employed in vitro digestion to investigate changes in bioactive substances, bioaccessibility, and antioxidant activity of PCH at different steam-bask times. It revealed the correlation between bioactive substances and antioxidant activity in PCH, and validated the ‘nine-steam-nine-bask’ process’s efficacy. In undigested samples, total phenol content (TPC), reducing sugar content (RSC), and DPPH and ABTS activities increased with more cycles, peaking in the nine-cycle sample at 7.627 mg GAE/g DW, 465.333 mg GE/g DW, 17.698, and 36.986 μmol VCE/g DW. Similar trends were observed throughout digestion. Total sugar (755.96 mg GE/g DW) and total saponin content (1.35 mg DE/g DW) plateaued during gastrointestinal digestion. Correlation analysis further revealed close relationships between bioactive substances and antioxidant activity. Multivariate statistical analysis confirmed that nine cycles maximized the distinction between steam-bask and non-steam-bask PCH.