## 1 Introduction  
Xylitol is a naturally occurring pentahydroxy sugar alcohol used as a natural food sweetener [1, 2]. It can be found in a wide variety of fruits, vegetables, berries, oats, and mushrooms, in amounts of less than 1 wt% [3]. This polyol has sweetness equivalent to sucrose but with a lower glycemic index, which makes it suitable for diabetes patients [4, 5]. Due to its anticariogenic properties, xylitol has also been used in the prevention of caries; it is a common component of sugar-free chewing gums [6, 7]. Additionally, the nutritional benefits of xylitol promote its use in several dietary supplements [8, 9], nutraceuticals [10, 11], and confectionary products [12]. Owing to its trend across food and pharmaceutical industries, in 2019 the xylitol global market exceeded 880 million USD, and it is further expected to expand to over 1 billion USD by 2026 [13]. On an industrial scale, xylitol is produced though the catalytic hydrogenation of xylose from xylose-enriched biomass, such as bichr wood, in a high energy-consuming and a nonenvironmentally friendly process [3]. Over the last decades, the biotechnological pathway has emerged as an ecological alternative for xylitol production because it involves milder conditions, low carbon emissions, and lower environmental disposal of chemicals [14]. Moreover, the use of lignocellulosic waste as a feedstock for microbial cultivation makes biotechnological processes economically sustainable [15, 16]. Various xylose-rich lignocellulosic waste, including corncobs [17], sugarcane bagasse [18], brewer's spent grain (BSG) [19], and rice straw [20], have been used as feedstock for the microbial production of xylitol. Due to their complex structure, lignocellulosic materials generally require pretreatment steps, such as dilute acid hydrolysis, to convert cellulose and hemicellulose into fermentable sugars, prior to their utilization as feedstocks for microbial cultivation. However, while maximizing the conversion of the carbohydrates into fermentable sugars, it is essential to minimize the carbohydrates losses during processing to ensure the cost-effectiveness of the pretreatment [21]. Such treatments can remarkably modify the physical-chemical properties of biomass and generate inhibitors by degradation of the formed products. Although it is a simple, rapid, and low-cost method, dilute acid hydrolysis generates several toxic compounds, namely furan derivatives and weak acids, which can act as microbial inhibitors, leading to slow kinetics, limited yields, and low productivities [15; 22]. In view of this, several detoxification methods, such as evaporation, neutralization, overlining, adsorption into ion-exchange resins, or activated charcoal, have been used to remove toxic compounds or reduce their concentration, thus increasing the hydrolysates' fermentability [23; 24]. The utilization of activated charcoal has arisen as a simple low-cost method for hydrolysates' detoxification, and its use significantly improved microbial cell growth as well as xylitol synthesis [25; 26]. Yeasts, especially those belonging to the genus _Candida_[27; 28; 29] that possess the enzymes required for xylose metabolism, are recognized as the most efficient xylitol producers [15]. However, the pathogenic nature of _Candida_ sp. is a barrier for the bioprocess implementation at an industrial scale, due to safety issues. An alternative is the use of genetically modified xylitol-producing yeasts (e.g., _Saccharomyces cerevisiae_ XP-RTK [30], _Pichia stipitis_ YS-30 [31]), but the legislation related with genetically modified organisms (GMOs) products also restricts their industrial use [32]. Therefore, the utilization of nonpathogenic and non-GMO microorganisms for the production of xylitol represents a promising strategy to overcome such issues and develop novel bioprocesses for this sugar alcohol production.