## 4 Discussion  
In recent decades, PDX, lacitol and xylitol have increasingly been investigated in gastrointestinal research, especially in those studies related to colon health. Their beneficial effects on colon epithelium are mostly achieved by the modification of microbiota and the production of SCFAs [16; 17; 18]. In concert with a previous study, xylitol fermentation mainly leads to a dramatic increase of butyrate [20]. In our study, PDX fermentation increased all three major SCFAs to a small extent, but not as much as lacitol and xylitol and not statistically differently to the control. Interestingly, although there are small increases in actual amounts, the proportion of individual SCFAs remained constant throughout V1 to V4, and the fermentation pattern was the same as reported in other studies [20; 21]. The reason that PDX fermentation only led to small insignificant increases may be attributed to its slow fermentation [28]. Because of its complex structure, PDX is gradually degraded and fermented by the colonic microbiota, and therefore leads to a sustained production of SCFAs from proximal to distal colon [17]. Our results also showed that lacitol fermentation increased acetate the most, followed by butyrate, which is consistent with the findings of \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**TEER**} & \multicolumn{2}{c}{**Permeability**} \\ \cline{2-5}  & \(\mathbf{r}\) & \(\mathbf{p}\) & \(\mathbf{r}\) & \(\mathbf{p}\) \\ \hline Actual concentration (mM) & & & & \\ Acetate & \(-0.096\) & \(0.293\) & \(-0.106\) & \(0.249\) \\ Propionate & \(0.055\) & \(0.543\) & \(-0.109\) & \(0.234\) \\ Butyrate & \(0.428\) & \(<\)0.001 & \(-0.391\) & \(<\)0.001 \\ Total SCFAs & \(0.204\) & \(0.024\) & \(-0.334\) & \(<\)0.001 \\ Proportion of total SCFAs & & & & \\ Acetate & \(-0.333\) & \(<\)0.001 & \(0.221\) & \(0.015\) \\ Propionate & \(-0.212\) & \(0.019\) & \(0.231\) & \(0.011\) \\ Butyrate & \(0.450\) & \(<\)0.001 & \(-0.368\) & \(<\)0.001 \\ \hline \hline \end{tabular} \(r\), [PERSON]’s correlation coefficient. \(p\), significant level, \(p<0.05\) was considered significant.  
\end{table} 
Table 2: Correlations between cellular parameters (TEER and permeability) and SCFAs. Figure 3: Effect of fermentation products on the epithelial barrier function. HT29-MTX-E12 cells were pre-treated with deoxynivalenol, and then 5% fermentation products of simulation control (SC), polydextrose (PDX), lacitol and xylitol were added. Transepithelial electrical resistance (TEER) and paracellular permeability data were obtained from four independent cell assays with duplicates (n = 8), and presented as mean values \(\pm\) SEM, relative to negative control (NC = 100%). NC indicates growth medium without FCS and fermentation products. V1-V4 indicates vessel 1 to vessel 4 in in vitro EnteroMix fermentation model. All fermentation products differed significantly with NC (\(p<0.001\)), and only differences between fermentation products are shown in the figure. Different lowercase letters indicate significant differences between four fermentation products within each vessel at \(p<0.05\) according to [PERSON]’s test. [PERSON] et al. [19]. However, [PERSON] et al. reported that the main SCFA in lacittol fermentation products is butyrate [29], whereas [PERSON] et al. showed that acetate and propionate increased by the same amount [30]. This inconsistency may be due to the difference in the in vitro fermentation methods. Few previous studies have reported that SCFA mixtures and in vitro fermentation products can improve intestinal barrier function [23; 31]. Our results also showed that all fermentation products increased TEER and decreased paracellular permeability of the compromised E12 cell monolayer, indicating that the production of SCFAs promotes intestinal barrier repair. Notably, despite the huge variation in actual SCFA concentrations, the fermentation products of PDX and lacittol did not provide additional benefits compared with SC.