Processing-Induced Changes in Polygonatum Bioactive Compounds: Mechanistic Implications for Gluten Protein Structure and Steamed Bread Quality

This study evaluated how Polygonatum processing affected its functional components, steamed bread quality, and gluten protein structure. Four-cycle extruded Polygonatum (EP-4) significantly enhanced antioxidant activity compared with raw Polygonatum (RP) and improved polysaccharides, flavonoids, and water-soluble extractives retention by 7.56%, 356.62%, and 8.15%, respectively, compared with nine cycles of steaming and sun drying Polygonatum (NP). RP, EP-4, and NP increased steamed bread antioxidant activity in the order NP > EP-4 > RP > control. However, all treatments increased hardness and chewiness while decreasing springiness and cohesiveness. The results suggested that RP limited protein aggregation, potentially through water competition and steric hindrance, whereas EP-4 promoted protein cross-linking, increasing dough stability time by 13.61% at 12% addition. NP showed signs of enhanced protein aggregation, reducing dough stability time by 39.92% and increasing adhesiveness 3.08-fold. SDS-PAGE and SDS-extractable protein analyses showed stronger low-molecular-weight bands and higher SDS-extractable protein content in RP, and band intensity partial recovery under reducing conditions in EP-4. Reduced SDS extractability at higher NP levels was consistent with increased protein aggregation. Overall, Polygonatum affected steamed bread quality via gluten aggregation, and EP-4 generally caused less deterioration than RP and NP.