## 3 Results and Discussion  
### Effects of Different Carbon and Nitrogen Sources on D. hansenii Growth and Enzymatic Activities  
The growth and metabolic characteristics of microorganisms are strongly influenced by the type and concentration of carbon and nitrogen sources in the medium, a factor closely related to the metabolic regulation mechanisms of the fermenting strain [21]. As shown in Figure 1A, the supplementation of different exogenous carbon and nitrogen sources significantly affected the proliferation of _D. hansenii_. Under carbon source treatment, the FCC group (corn starch) exhibited a colony count of 1.00 \(\times\) 10\({}^{10}\) CFU/g, which was significantly higher than that of the control group, 8.70 \(\times\) 10\({}^{9}\) CFU/g (\(p\) < 0.05). This result was likely due to the slow-release property of corn starch, which may provide a stable energy supply to support sustained cell activity. In contrast, the FCS group (sucrose) showed a 40.23% decrease in colony count, which may be associated with osmotic stress. According to [PERSON] et al., under high-salt stress conditions, _D. hansenii_ tends to allocate energy to maintaining cellular homeostasis rather than promoting rapid cell division [22]. Under nitrogen source treatment, both the FNL group (leucine) and the FNP group (soy protein isolate) significantly increased colony counts. The FNP group exhibited the highest colony count at 1.66 \(\times\) 10\({}^{10}\) CFU/g, representing a 90.23% increase compared to the control (\(p\) < 0.05). This enhanced proliferation may be attributed to the higher nitrogen content (-15%) and more complex nitrogenous composition of soy protein isolate, compared to leucine (-10.7%). Upon hydrolysis, soy protein isolate releases a broad spectrum of amino acids and peptides, which may more effectively support the synthesis of nucleic acids, proteins, and cofactors essential for cell proliferation. In contrast, the FNL group was supplemented with a single amino acid. Although leucine modestly enhanced growth, its limited nitrogen profile may not have met the broader metabolic requirements of the strain. Protease and lipase are two crucial enzymes produced by _D. hansenii_ during fermentation; they are involved in the hydrolysis of proteins and fats, respectively, thereby enhancing the flavor profile of fermented meat products [23]. As shown in Figure 1B, protease activity was significantly higher in all treatment groups compared to the control group, with the FNP group exhibiting the highest activity at 55.38 U/g, approximately 5-fold higher than the control and 2-fold higher than the other treatment groups (\(p<0.05\)). These results indicate that exogenous carbon and nitrogen supplementation enhanced the protease activity in _D. hansenii_, with various sources potentially affecting the strain through distinct nutritional pathways or physiological effects. Carbon sources can indirectly stimulate protease synthesis by providing carbon skeletons and an efficient energy supply to sustain high metabolic activity, while nitrogen sources can boost metabolic activity and enhance protease expression by supplying essential nitrogen [24]. In addition, soy protein isolate, as a high-molecular-weight protein, may serve as a substrate for extracellular proteases, potentially enhancing protease activity through substrate-enzyme recognition [25]. The elevated activity observed in the treatment groups may facilitate the release of amino acids and peptides--key precursors of flavor compounds--enhancing the umami and aromatic complexity of the final product. Figure 1C shows that exogenous carbon and nitrogen sources did not significantly affect the lipase activity of _D. hansenii_. This may be because lipase is an inducible enzyme, and its synthesis typically depends on the presence of specific lipid substrates acting as inducers [26]. It is possible that the carbon and nitrogen sources used in this experiment lacked the specific components required to induce lipase expression.