# Stability and Bioaccessibility of \(\beta\)-Arbutin in Simulated Digestion Conditions
## 4 Discussion
At both the gastric and intestinal steps of digestion, the application of the biochemical factors resulted in a slight and in most cases statistically insignificant decrease in the bioaccessibility of \(\beta\)-arbutin, especially when the higher doses were applied (Figure 1). This suggests that the association of \(\beta\)-arbutin with the biochemical components of the digestion fluids was at a very low, insignificant level, in particular at the gastric digestion stage. Even so, a statistically significant decrease in bioaccessibility was observed after the intestinal digestion process when \(\beta\)-arbutin was applied at the lowest doses (1 and 2.5 mg). Compared to gastric digestion, at the intestinal digestion stage, the concentration of biochemical components in the digestion fluids that can potentially interact with the administered compound was much higher (i.e., besides the popsin remaining after gastric digestion, pancreatic enzymes and bile components were introduced), which at a low concentration of \(\beta\)-arbutin resulted in a significant decrease in its bioaccessibility (expressed as the relative value), despite the fact that the relatively very low amount (expressed quantitatively) of this compound was bound (Table 1). The association of phenolic substances with digestion enzymes and other biochemical components of digestion fluids is determined by--in addition to the concentrations of interacting molecules and properties of the surrounding environment (temperature, pH, ionic strength, the occurrence of other compounds)--the chemical structure and physicochemical character of compounds [25; 26; 27; 31]. Some review reports suggest that the binding affinity of phenolic compounds to proteins, including digestion enzymes, increases with the molecular size of phenolic compounds and the number of phenolic moieties in the molecule [25; 27]. Since \(\beta\)-arbutin is a simple low molecular phenol, it may be presumed that its chemical character contributes to its general low binding affinity. Unfortunately, literature data concerning interactions of phenolic compounds with bile components are limited, and the binding affinity of phenolic compounds under the influence of their chemical character has not been reported. Some reports indicate that instability of \(\beta\)-arbutin caused by oxidative degradation may lead to the release of free hydroquinone, whose excessive level may pose some risk of toxicity caused by its relatively high reactivity; thus, monitoring its level and determination of factors influencing the stability of \(\beta\)-arbutin seems important given the potential biological consequences of its application in an isolated form [6; 14; 15]. Interestingly, the analysis of chromatograms obtained for in vitro bioaccessible fractions showed that, at both the gastric and intestinal stage in the simulated digestion environment, the production of free-state hydroquinone was not induced, even when the lowest doses were applied (as those characterised by the lowest stability and bioaccessibility) (Figure 2). Previous reports considering the chemical stability of \(\beta\)-arbutin suggest that its oxidative degradation can also result in the formation of byproducts other than hydroquinone and/or the probable subsequent conversion of the released hydroquinone to other derivatives [14]. In addition, it has been reported that the abundance of free-state hydroquinone can be favoured in the case of the application of complex mixtures of naturally occurring phytochemicals containing \(\beta\)-arbutin (e.g., from bearberry leaves), where co-compounds may catalyse its degradation, and free hydroquinone (in addition to its natural plant material origin) may come from the degradation of hydroquinone-containing compounds other than \(\beta\)-arbutin [14]. So far, the experimental data concerning the potential \(\beta\)-arbutin behaviour in digestion system conditions are very limited. Despite the differences in the simulated digestion conditions, a study conducted by [PERSON] et al.