## 3 Results and Discussion
### Analysis of Characteristic Volatile Compounds
We further performed hierarchical clustering analysis on the 21 characteristic volatile compounds, as shown in Figure 7. The results indicate significant differences in the characteristic volatile compounds among the YCSP, YMMP, and YEMP samples, with noticeable variations in the content of these compounds across different yak milk powder samples. The results of the analysis of characteristic volatile compounds indicate significant differences among the YCSP, YMMP, and YEMP samples. Previous studies on flavor compounds in yak milk and yak milk powder have found that factors such as the origin of the milk [8], fermentation strains [2], sterilization methods [28], drying methods [27], and storage conditions [13] can all affect the types and concentrations of volatile compounds in yak milk. In this study, we controlled for these factors by using samples collected from yak milk powder at different lactation periods to specifically investigate the differences in volatile compounds. Compared to volatile compounds in other milk powders, we found that yak milk powder has unique volatile compound characteristics, such as fatty acids and fatty acid esters, which may be related to its growing environment and feeding practices [42]. Although HS-SPME-GC-MS offers high sensitivity, it also has some limitations, such as potential interference from other components in complex samples and lower extraction efficiency for certain compounds. To improve detection accuracy, future studies could combine other analytical methods, such as liquid chromatography-tandem mass spectrometry (LC-MS/MS) [43]. The results of this study can help dairy manufacturers optimize their processes, especially in enhancing the flavor of yak milk, by selecting specific processing techniques or additives to retain key volatile compounds, ensuring consistency in flavor and quality. In this study, the types and concentrations of volatile compounds in different yak milk powder samples determined their flavor and aroma. Fatty acid esters typically have sweet and fruity aromas, which are highly appreciated in dairy products [16]. The higher concentration of these compounds in YMMP may explain its richer, more complex flavor. Understanding how these compounds affect flavor will help improve the production  
Figure 7: Hierarchical clustering heatmap analysis of identified volatile compounds in yak milk samples from different lactation periods. The vertical axis represents the sample numbers from different lactation periods, and the horizontal axis represents the names of the detected volatile compounds. Blue blocks indicate relatively low content, while red blocks indicate relatively high content. processes and quality control of yak milk products. Additionally, this study did not focus on the significant impact of climate and feeding conditions on the composition of volatile compounds in yak milk powder. As this factor is related to the formation of flavor compounds in yak milk, future research should focus on how environmental factors influence the volatile components in yak milk. It must be emphasized that the results of this study have important practical value for the dairy industry, particularly to produce high-quality yak milk powder. By understanding the volatile compound composition in yak milk at different lactation stages, producers can optimize processing conditions to enhance flavor while maintaining nutritional integrity. Moreover, the volatile biomarkers identified in this study can be used for quality control, ensuring consistency in flavor and aroma in commercial production. Additionally, by identifying the characteristic aromatic volatile compounds in yak milk powder, producers can adjust their manufacturing processes to create products that are more appealing to consumers. This is particularly important as yak milk enters the market as a new product, as understanding consumer flavor preferences can guide the production of products with broad market acceptance.