Sourdough-Yeast Co-Fermentation Preserves Frozen Raw Stuffed-Bun Quality.

Frozen raw steamed stuffed buns lose volume and harden during storage, limiting industrial quality retention. Here, we evaluated 0%, 30%, 50%, 70%, and 100% sourdough addition in a sourdough-yeast co-fermentation system and examined microbial, metabolic, and gluten-related changes. At 30% addition, the dough reached a maximum height of 47.7 mm and produced the best overall product quality. After 30 days at -18 °C, this group retained the highest specific volume, approximately 21% above the control, together with lower hardness and higher sensory scores. Yeast and lactic acid bacteria (LAB) counts remained at 6.21 and 7.50 lg CFU/g, respectively, and proline accumulation was positively correlated with greater freeze tolerance, suggesting that it may play a role in cryoprotection, but the causal relationship remains to be further experimentally verified. Free sulfhydryl content increased by 6.25%, compared with 73.02% in the control, indicating less disruption of gluten disulfide bonds. Therefore, under the experimental conditions employed in this study (specific wheat flour, sourdough fermentation system, and 30-day frozen storage), the 30% sourdough addition level exhibited the best overall quality improvement, probably through coordinated microbial metabolism and preservation of the gluten network. These findings support the use of sourdough-yeast co-fermentation in frozen flour products.