## 3 Results and Discussion
### Influence of the Oral Coating Formed by Peanut Lipid on Baijiu Aftertaste  
The mass transfer coefficient is the main factor affecting the aroma release in the oral cavity [22]. The Intraoral SPME method was used to study this process in baijiu drinking (Figure 4). In the lipid-free condition, the release intensity of the compound decreased non-linearly, indicating the retention effect of the oral mucosa to baijiu, which significantly affects its aftertaste [23]. The release pattern of baijiu aroma compounds in the oral cavity is driven by the retention ability of oral mucosa, ranked as follows: alcohols \(>\) aromatic compounds \(>\) esters \(=\) pyrazines \(>\) phenols \(>\) aldehydes \(>\) acids. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \(\mathbf{E_{\text{solv,polar}}}\) & \(\mathbf{E_{\text{solv,nonpolar}}}\) & \(\mathbf{E_{\text{MM}}}\) & \(\mathbf{E_{\text{ele}}}\) & \(\mathbf{E_{\text{vdw}}}\) \\ \hline ELA-OOL & \(2.322\) & \(-1.437\) & \(-5.020\) & \(-0.298\) & \(-4.722\) \\ ELA-OLL & \(2.651\) & \(-1.148\) & \(-5.693\) & \(-0.485\) & \(-5.208\) \\ ELA-POL & \(1.154\) & \(-1.053\) & \(-2.793\) & \(-0.064\) & \(-2.729\) \\ EHE-OOL & \(4.750\) & \(-5.604\) & \(-21.408\) & \(-0.386\) & \(-19.001\) \\ EHE-OLL & \(4.595\) & \(-5.103\) & \(-19.605\) & \(-0.408\) & \(-19.197\) \\ EHE-POL & \(2.775\) & \(-3.340\) & \(-11.735\) & \(-0.199\) & \(-11.536\) \\ HEC-OOL & \(3.679\) & \(-4.554\) & \(-14.615\) & \(-0.122\) & \(-14.493\) \\ HEC-OLL & \(3.629\) & \(-4.661\) & \(-15.458\) & \(-0.326\) & \(-15.132\) \\ HEC-POL & \(4.901\) & \(-4.701\) & \(-16.679\) & \(-0.372\) & \(-16.307\) \\ \hline \hline \end{tabular} EHE is for ethyl hexanoate. ELA is for ethyl lactate. HEC is for heptanoic acid. OOL, OLL, and POL is the triglyceride of peanut lipid, O is for oleic acid, L is for linoleic acid, and P is for palmitic acid.  
\end{table} 
Table 3: Interaction energy between molecules. Figure 4: Release intensity of compounds at 0 s and 120 s in the in vivo experiment of baijiu aroma compounds under the influence of mouth coating formed by peanut lipid. The “**” represents \(p\) < 0.05, “**” represents \(p\) < 0.001, and “**”ns” represents no significant difference in the multiple \(t\)-test. **  
Figure 4 presents a comparison between 0 s and 120 s in the lipid-free and lipid-coating groups. At 0 s, the lipid weakened the release intensity of all target compounds, consistent with the in vitro experiments. Notably, the release intensities of ethyl hexanoate, nonanal, 2,3,5-trimethylpyrazine, ethyl octanoate, phenylacetaldehyde, nonanol, decanol, and ethyl phenylacetate decreased significantly. Particularly, nonanal with rose and orange aroma decreased by 79.5%, and phenylacetaldehyde with sweet aroma decreased by 63.5%. Aldehydes have a high retention rate in the lipid, followed by the esters. The release intensities of ethyl heptanoate and ethyl octanoate decreased by 60.6% and 71.2%, respectively, while ethyl hexanoate had a relatively low decrease proportion of 32.3%. The decrease in phenolic compounds was minimal, with phenol decreasing by only 15.3%. The intensity reductions at 0 s under the influence of peanut lipid in vitro and in vivo were similar, especially for phenol, phenylacetaldehyde, 4-ethylphenol, 1-decanol, ethyl phenylacetate, butyric acid, octanoic acid, heptanoic acid, 2-heptanol, tetramethyl pyrazine, trimethyl pyrazine, p-cresol, and ethyl hexanoate. These could be retained in the mouth coating and contribute to aftertaste perception. For alcohols and esters, their in vivo decrease proportions were slightly lower than in vitro due to oral mucosa retention. However, for some compounds like nonanal, ethyl heptanoate, and ethyl octanoate (with relatively high \(\log p\) values), the in vivo decrease proportions under the influence of lipid were much greater than those in the headspace experiment, possibly due to the spitting process in the experimental procedure. Compared to the in vitro experiment, many other factors influenced aroma release in vivo.