# Effect of Whey Protein Changes on Milk Flavor and Sensory Characteristics During Heating
## 3 Results and Discussion
### VOCs Characteristics of Different Heat-Treated Milk
\begin{table}
\begin{tabular}{c c c c c} \hline
**Sample** & **\(\alpha\)-Helix (\%)** & **\(\beta\)-Sheet (\%)** & **\(\beta\)-Turn (\%)** & **Random Coil (\%)** \\ \hline Raw & 15.5 \(\pm\) 0.08 \({}^{\mathrm{c}}\) & 34.6 \(\pm\) 0.08 \({}^{\mathrm{a}}\) & 19.6 \(\pm\) 0.00 \({}^{\mathrm{s}}\) & 30.3 \(\pm\) 0.08 \({}^{\mathrm{e}}\) \\
6010 & 25.1 \(\pm\) 0.05 \({}^{\mathrm{b}}\) & 8.4 \(\pm\) 0.05 \({}^{\mathrm{e}}\) & 21.4 \(\pm\) 0.12 \({}^{\mathrm{e}}\) & 45.1 \(\pm\) 0.21 \({}^{\mathrm{a}}\) \\
6030 & 27.2 \(\pm\) 0.05 \({}^{\mathrm{a}}\) & 8.3 \(\pm\) 0.05 \({}^{\mathrm{e}}\) & 20.5 \(\pm\) 0.00 \({}^{\mathrm{f}}\) & 43.9 \(\pm\) 0.05 \({}^{\mathrm{b}}\) \\
7510 & 12.5 \(\pm\) 0.05 \({}^{\mathrm{d}}\) & 30.4 \(\pm\) 0.19 \({}^{\mathrm{d}}\) & 25.3 \(\pm\) 0.05 \({}^{\mathrm{b}}\) & 31.8 \(\pm\) 0.19 \({}^{\mathrm{c}}\) \\
7530 & 9.8 \(\pm\) 0.05 \({}^{\mathrm{f}}\) & 34.8 \(\pm\) 0.05 \({}^{\mathrm{a}}\) & 24.0 \(\pm\) 0.05 \({}^{\mathrm{d}}\) & 31.3 \(\pm\) 0.00 \({}^{\mathrm{d}}\) \\
10010 & 9.4 \(\pm\) 0.05 \({}^{\mathrm{g}}\) & 33.6 \(\pm\) 0.12 \({}^{\mathrm{b}}\) & 25.0 \(\pm\) 0.08 \({}^{\mathrm{c}}\) & 32.0 \(\pm\) 0.08 \({}^{\mathrm{c}}\) \\
10030 & 11.0 \(\pm\) 0.05 \({}^{\mathrm{e}}\) & 32.1 \(\pm\) 0.29 \({}^{\mathrm{c}}\) & 26.3 \(\pm\) 0.09 \({}^{\mathrm{a}}\) & 30.6 \(\pm\) 0.26 \({}^{\mathrm{e}}\) \\ \hline \end{tabular} \({}^{\mathrm{a}}\)-\({}^{\mathrm{b}}\) According to the Tukey test, different superscripts in the same column indicate significant differences (_p_ < 0.05).  
\end{table} 
Table 1: Changes in the structural whey protein content after different heat treatments. with a relative content of 91%. This was consistent with the findings of [PERSON] et al. (2018), who found that the acid content in raw milk was significantly higher than in milk treated at 65 \({}^{\circ}\)C and 135 \({}^{\circ}\)C for 30 min. Furthermore, the total VOC content in the milk samples increased gradually at higher temperatures, as shown by 6010 \(\approx\) 6030 \(<\) 7510 \(<\) 10010 \(<\) 7530 \(<\) 10030 (Figure 2A). At the same heating temperature, the total VOC content increased as the heating time was extended. Principal component analysis (PCA) was used to compare the differences between the VOCs in the seven milk samples (Figure 2C). The results showed a cumulative variance contribution of 79.6%, indicating that the 3D PC covered most of the odor information of all the samples. The raw, 7530, and 10030 groups were clustered into one category. Additionally, 6010 and 6030 were clustered into one group, while 7510 and 10010 were grouped into another, indicating that their overall flavors were similar. A cluster heat map was used to illustrate the classification and comparability of the flavor compounds produced in the milk exposed to different heat treatments (Figure 2D). The raw group displayed a relatively high acid content compared to other samples. The VOC levels in 6010 and 6030 were fairly low and clustered into one group, which was consistent with the PCA results. The VOC content in 10010 and 7510 was higher than in 6010 and 6030 but lower than milk samples heated at the same temperature for 30 min. The 10030 and 7530 milk samples displayed high VOC levels and were grouped together. Figure 2: The VOCs identified via HS-SPME-Arrow-GC-MS in the milk after different heat treatments. (**A**) The relative VOC content. (**B**) The relative VOC content percentage. (**C**) The PCA analysis of the VOCs. (**D**) The clustering heat map analysis of the VOCs.