## 3 Results
### E-Tongue Analysis  
The results of using E-tongue are shown in Table 3. The sourness has a tasteless threshold of \(-13\), saltiness has a tasteless threshold of \(-6\), and other indicators have a tasteless threshold of \(0\). When the taste value of the sample is lower than the tasteless threshold, this indicates that the sample has no such taste; when it is higher than the tasteless threshold, this indicates that the sample has this taste [25]. All samples have higher response values for bitterness, umami and sweetness, but lower response values for Aftertaste-B and Aftertaste-A. The 135 \({}^{\circ}\)C-treated milk had a significantly higher bitterness  
Figure 1: PCA of milk with different processing temperatures.  
Figure 2: Radar map of VOCs in milk processed using different temperatures.  
response value than the raw milk and the 65 \({}^{\circ}\)C-treated milk (\(p<0.05\)). The sweetness response differed--the 135 \({}^{\circ}\)C-treated milk was significantly less sweet than the raw milk and the 65 \({}^{\circ}\)C-treated milk (\(p<0.05\)). This point was also confirmed in the subsequent GC-MS detection. The furfural content increased significantly due to the increase in processing temperature, and furfural presented a burnt bitterness to the outside. Milk becomes more bitter and less sweet as it is processed at higher temperatures.  
As shown in Figure 3A, the OPLS-DA model was established according to the test results of E-tongue, andthe model (R2X = 0.972, R2Y = 0.806, Q2 = 0.765) showed good discriminant and predictive ability. The E-tongue accurately distinguished milk samples with different heat treatments, which indicated that temperatures lead to apparent differences in milk taste. The load diagram explains the taste contribution of different heat-treated milk. Raw milk is located in the fourth quadrant, close to sweet and Aftertaste-B, indicating that sweet and Aftertaste-B are the primary taste manifestations of raw milk; 65 \({}^{\circ}\)C-treated milk is located in the first quadrant, close to saltiness, and its primary taste is saltiness; 135 \({}^{\circ}\)C-treated milk is located in the third quadrant, close to bitterness, and its primary taste is bitterness (Figure 3B).  
Figure 3: OPLS-DA 2D score map of milk E-tongue with different temperatures (**A**) and load diagram (**B**).  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & **Sourness** & **Salitness** & **Bitterness** & **Asttingency** & **Aftertaste-B** & **Aftertaste-A** & **Umami** & **Sweetness** & **Aftertaste-U** \\ \hline Tasteless & \(-13\) & \(-6\) & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) \\ Raw milk & \(-45.71\pm 0.14\) c & \(0.18\pm 0.44\) b & \(7.81\pm 0.19\) b & \(1.94\pm 0.18\) b & \(1.00\pm 0.07\) a & \(0.37\pm 0.03\) a & \(6.79\pm 0.11\) b & \(11.08\pm 0.23\) a & \(4.91\pm 0.11\) b \\
65 \({}^{\circ}\)C & \(-41.41\pm 0.15\) b & \(3.29\pm 0.44\) a & \(7.88\pm 0.25\) b & \(3.19\pm 0.14\) a & \(0.18\pm 0.19\) b & \(0.33\pm 0.02\) a & \(7.21\pm 0.08\) ab & \(8.92\pm 0.17\) b & \(6.59\pm 0.22\) a \\
135 \({}^{\circ}\)C & \(5.77\pm 4.36\) a & \(1.43\pm 1.70\) ab & \(15.10\pm 2.10\) a & \(2.37\pm 0.71\) ab & \(0.07\pm 0.08\) b & \(0.18\pm 0.04\) b & \(7.73\pm 0.95\) a & \(8.35\pm 0.35\) c & \(1.18\pm 0.26\) c \\ \hline \end{tabular}
\end{table}
Table 3: Taste value of milk E-tongue with different processing temperatures.