Fermentation Strategy and Non-Saccharomyces Yeast Strain Identity Jointly Shape Volatile Profiles in Chinese Steamed Bread Produced with Defined Composite Sourdoughs.

Chinese steamed bread (CSB) is an important fermented wheat product, but controlled strategies for modulating its volatile profile remain limited. This study evaluated defined composite sourdoughs comprising Wickerhamomyces anomalus CRFSZY16 or Kluyveromyces marxianus FYY7 in combination with Lactiplantibacillus plantarum SDgsM3 for CSB production using the direct fermentation method (DFM) and the refrigerated sponge-dough method (RSDM). Technological stress tolerance, preliminary safety-related phenotypes, acidification capacity, volatile organic compounds (VOCs), multivariate profiles, and specific volume were assessed. SDgsM3 showed dough-relevant stress tolerance and rapid acidification, while both yeasts tolerated moderate fermentation stresses. Headspace solid-phase microextraction coupled with gas chromatography-triple quadrupole mass spectrometry (HS-SPME-GC-TQ-MS) revealed stage-dependent remodeling of volatile profiles from mature sourdough to fully proofed main dough and final CSB. RSDM selectively modified representative alcohols, aldehydes, furans, ketones, and esters rather than uniformly increasing all VOCs. In the final CSB, the K. marxianus-based RSDM system showed relatively higher levels of 3-methyl-1-butanol, whereas the W. anomalus-based RSDM system showed relatively higher levels of hexanal, nonanal, 1-hexanol, and 2-pentylfuran. Composite sourdough treatments also yielded specific volumes of 2.56-2.66 mL/g versus 2.44 mL/g for the commercial yeast control. These findings demonstrate strain- and process-dependent modulation of CSB volatile profiles and support flavor-oriented composite sourdough design.