# Effect of Whey Protein Changes on Milk Flavor and Sensory Characteristics During Heating
## 3 Results and Discussion
### Correlation Analysis  
PLSR was used to assess the correlations between the sensory attributes and VOCs (Figure 4). Most flavor compounds are located on the positive axis and are positively correlated with milky, dairy fat, cooked, and oxidized aromas. However, higher temperatures increased the types and levels of flavor compounds in the milk samples. The raw sample contained high levels of hexanoic acid, butyric acid, heptanoic acid, and other acid compounds. Both the raw sample and grassy flavor were located in the third quadrant. This indicated that the raw samples exhibited a stronger grassy taste, which was consistent  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Descriptors** & **Raw** & **6010** & **6030** & **7510** & **7530** & **10010** & **10030** \\ \hline Milky aroma & 4.17  & 5.75  & 5.67  & 5.17  & 5.75  & 6.58  & 6.17  \\ Dairy fat & 4.50  & 5.42  & 5.25  & 5.17  & 6.25  & 5.83  \\ Cooked & 2.83  & 2.75  & 4.25  & 4.17  & 4.08  & 3.67  & 4.33  \\ Oxidized & 1.75  & 2.42  & 3.25  & 3.83  & 3.75  & 2.83  & 3.75  \\ Grassy & 2.83  & 1.92  & 2.17  & 2.33  & 2.58  & 2.00 [FOOTNOwith the sensory evaluation score. Similarly, 10030 and 10010 were located in the first quadrant, indicating that both displayed strong milky, dairy fat, and cooked aromas, which was also consistent with the sensory evaluation results.  
A correlation plot was created to investigate the association between whey protein denaturation and flavor compounds (Figure 5). The results showed that both \(\alpha\)-LA and \(\beta\)-LG were negatively correlated with 1-butanol, 1-hexanol, 1-octen-3-ol, 1-octanol, butyric acid, hexanoic acid, pentyl formate, and positively associated with other compounds. The strongest negative correlation was evident between \(\beta\)-LG and 1-octen-3-ol (\(p\leq 0.05\)). In addition to these compounds, LF was negatively correlated with pentanoic, heptanoic, and octanoic acid, showing the strongest negative correlation with 1-octen-3-ol (\(p\leq 0.01\)). A strong positive correlation was evident between \(\alpha\)-LA and hexanal, undecanoic acid, \(\delta\)-hexalactone, 6-propyltetrahydro-2\(H\)-pyran-2-one, 6-pentyltetrahydro-2\(H\)-pyran-2-one, and methyl palmitate (\(p\leq 0.001\)), while \(\beta\)-LG showed the strongest positive association (\(p\leq 0.001\)) with hexanal, isovaleric acid, and methyl palmitate. Overall, the three active proteins were positively associated with hexanal, isovaleric acid, \(\gamma\)-nonalactone, methyl palmitate, and phenol (\(p\leq 0.01\)). The relationship between whey protein denaturation and these flavor compounds can be further explored in future studies.  
Figure 4: The PLSR results of the sensory evaluation and VOCs of milk under different heat treatment conditions.  
Figure 5: The correlation plot of the active proteins and VOCs in the milk exposed to different heat treatments.  
To explore the correlation between milk flavor compounds and whey protein denaturation as comprehensively as possible, this study used whole milk to produce a significant variety of VOCs. However, due to the complex composition of milk, the fat and lactose it contains may also react or interact with flavor compounds. Subsequent experiments can further explore the effects of fat and lactose on flavor compounds. And experiments can also be conducted with whey protein monomers and compound standards to further explore the correlation between milk whey protein and VOCs, while new techniques can be employed for more comprehensive analysis. For example, molecular docking techniques and molecular dynamics simulations are used to predict the binding mode and affinity of samples by simulating the forces and sites of interaction between proteins and flavor compounds [53].