# Stability and Bioaccessibility of \(\beta\)-Arbutin in Simulated Digestion Conditions
## 1 Introduction  
Arbutin is a common name for a hydrophilic phenolic glycoside composed of a hydroquinone moiety bound to D-glucose. It exists in two forms differentiated by the anomeric carbon conformation, i.e., \(\alpha\)-arbutin (4-hydroquinone-\(\alpha\)-d-glucopyranoside) and \(\beta\)-arbutin (4-hydroquinone-\(\beta\)-d-glucopyranoside) [1, 2, 3]. In comparison with \(\alpha\)-arbutin, which is chemically synthesised or synthesised via biocatalytic routes, \(\beta\)-arbutin is a natural secondary plant metabolite [2, 4]. It has been found in approximately 50 plant families; notably, the Ericaceae family is abundant in this compound, of which the beaberry plant (_Arctostaphylos uwu-ursi_ (L) [PERSON]) is regarded as its main botanical source [3, 5]. Synthetic \(\alpha\)-arbutin is commonly applied in cosmetics for skin lightening as a more effective dermal contact agent than its natural analogue [2, 6]. Nevertheless, due to general consumers' preferences for using natural substances, considerable attention has recently been paid to \(\beta\)-arbutin, which is considered a promising health-promoting or therapeutic agent in addition to its dermal applications [2]. Previously, a multitude of biological activities of \(\beta\)-arbutin was reported, with the best-known being diuretic and antiseptic activity in the treatment of various lower urinarytract infections [5; 6; 7]. Other relevant properties of \(\beta\)-arbutin include antioxidant, anti-inflammatory, antidiabetic, anti-hyperlipidaemic, antidepressant, immunomododulatory, cytoprotective, and wound healing activity, among others [3; 6]. Furthermore, it is regarded as a substance with anticancer potential due to a wide range of cytotoxic activity, including its effects on brain, breast, gastric, colon, liver, bladder, prostate, and bone human cancer cell lines [3]. Nevertheless, to exert their desirable pharmacological functions, bioactive compounds should be characterised by adequate supply, bioaccessibility, and bioavailability. Taking into account oral administration, bioaccessibility can be defined as the portion of an ingested substance that is released or remains after digestion and can be absorbed in vitro; therefore, this may be regarded as the main limiting factor of its future fate and utilisation in an organism, i.e., bioavailability (which reflects a portion of absorbed substance that can be distributed to cells and tissues), and finally bioactivity (the activity in living systems) [5; 8; 9]. On the one hand, the physicochemical digestion environment, including pH, temperature, and interactions with electrolytes, can negatively affect the chemical stability of phytochemicals; on the other hand, complexation with the biochemical components of digestion fluids (enzymes and bile components) may decrease their concentration in the free, uncomplexed form, consequently restricting their final bioaccessibility [8; 10]. Due to their specific chemical character, phenolic substances are considered particularly susceptible to degradation and complexation; thus, their interactions with the digestion environment are an increasingly common research target [9; 11; 12; 13]. At present, little is known about the behaviour of \(\beta\)-arbutin in the digestion environment and its resulting bioaccessibility. Moreover, because one of the potential products of its degradation is free hydroquinone, which raises some doubts concerning its toxicological safety, special attention is paid to the stability of \(\beta\)-arbutin [6; 14; 15; 16; 17]. Therefore, the objective of this study is to determine the effect of the physicochemical and biochemical environment on \(\beta\)-arbutin stability and bioaccessibility in simulated digestion conditions.