Dough pre-fermentation combined with refrigeration for selenium-enriched steamed bread: A balanced strategy to coordinate selenium biotransformation and quality

Se-enriched Chinese steamed bread (CSB) is a promising dietary Se source. This study prepared Se-enriched CSB using direct-fermented dough (DFD, 4-16 h) and pre-fermented refrigerated dough (PRD, 24-72 h) with Na₂SeO₃ at 500 or 1500 μg Se/kg. Selenomethionine predominated in DFD, whereas selenocystine dominated in PRD. Both processes enabled selenoamino acid conversion, but conversion efficiency at 1500 μg Se/kg was approximately half that at 500 μg Se/kg. Compared with DFD-CSB, PRD-CSB generally showed lower hardness, remaining within 4.76-7.05 N. Refrigeration for 24-48 h improved dough extensibility and produced CSB with a relatively uniform pore structure, although slight separation appeared in PRD-48 CSB at 1500 μg Se/kg. After 72 h, dough tenacity and extensibility declined, and all PRD-CSB exhibited crust-crumb separation, most pronounced at 1500 μg Se/kg. Thus, 24-48 h was suitable for PRD, whereas prolonged refrigeration and higher Se supplementation increased quality risks.