## 4 Conclusions  
In conclusion, this study showed the feasibility of improving the aroma profiles of soybean protein hydrolysates through fermentation with _T. halophilus_ and _Z. rouxii_. The combination of GC-MS and GC-IMS provided a comprehensive and effective analysis of VFCs, revealing substantial changes in their composition and concentration post-fermentation. LAB-yeast fermentation could increase the contents of alcohols, acids, esters, and sulfurs while decrease the contents of aldehydes and ketones. A total of 25 VFCs (ROAV > 1) were identified as key contributors for explaining the distinct aroma profiles among the three soybean protein hydrolysates. Notably, LAB-yeast fermentation not only diversified the array of key volatile flavor compounds but also shifted the flavor profile from predominantly beauty and fatty to more desirable attributes, like fruity, caramel, malt, and wine notes. Particularly, sequential inoculation emerged as a more effective approach in enhancing the overall aroma, as evidenced by the PLSR analysis. These findings offer novel insights into aroma enhancement strategies for soybean protein hydrolysates, highlighting the potential of fermentation for improving the sensory qualities of food products. Future research may investigate the relationship between the volatile compounds and microbial metabolism. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/foods12244513/s1](https://www.mdpi.com/article/10.3390/foods12244513/s1)]([https://www.mdpi.com/article/10.3390/foods12244513/s1](https://www.mdpi.com/article/10.3390/foods12244513/s1)), Table S1: Concentrations of volatile flavor compounds in different soybean protein hydrolysates analyzed by GC-MS. Table S2: The relative contents of volatile flavor compounds in different hydrolysate groups by GC-IMS. Figure S1: Venn diagrams of the volatile flavor compounds in different hydrolysate groups detected by GC-MS and GC-IMS. A, B and C represent the SH-0, SH-1 and SH-2 groups, respectively. **Author Contributions:** C.C. : Investigation, Formal analysis, Software, Writing--original draft. G.L.N.W. : Software, Supervision. W.S. : Investigation, Supervision. M.Z. : Supervision. D.S.-W.: Writing--review & editing, G.S. : Writing--review & editing, Funding acquisition. All authors have read and agreed to the published version of the manuscript. **Funding:** The study was financially supported by the Natural Science Foundation of China (32172329), the Natural Science Foundation of Guangdong Province (2022A1515010060), and the Science and Technology Program of Qingyuan (2022 KJJH018). Figure 5: Partial least squares regression (PLSR) analyses of key volatile compounds. (**A**) Cross validation diagram (\(n\) = 200); (**B**) Biplot loadings; (**C**) variable importance in projection values; (**D**) observation and prediction diagram. A1, A2, and A3; B1, B2, and B3; and C1, C2, and C3 denote the three replicates of the SH-0, SH-1, and SH-2 groups, respectively. The Var ID numbers are consistent with the compound numbers in Table 1.  
**Institutional Review Board Statement:** Ten experienced panelists (six females and four males, aged 20-28 years) from South China University of Technology (Guangzhou, China) were invited to evaluate the odors of soybean hydrolysate samples in the laboratory (23 \(\pm\) 2 \({}^{\circ}\)C) complied with international standards (ISO 8589: 2007) under normal lighting. These sensory assessors received sensory training according to ISO 8586:2023, the international standard approach for training and supervising assessors, and possessed over one year of experience in evaluating the sensory characteristics of various food samples. The procedures for participant recruitment and consent acquisition were rigorously conducted in accordance with the ethical guidelines in the Declaration of Helsinki. Informed consent was obtained from each assessor before starting sensory evaluation.