Detoxification strategies applied to lignocellulosic hydrolysates for improved xylitol production

Hemicellulose is the second most abundant renewable biomass after cellulose on the planet. It is one of the three heterogenous polymers, derived from lignocellulose biomass which yields individual sugars, mainly xylose after dilute acid or hydrothermal pretreatment. Among the microbial co-products generated from hemicellulose sugars, xylitol is the most abundant and holds the most valued potential in numerous medical and non-medical applications. During the hemicellulose hydrolysis, in addition to the production of sugars, a number of plant cell wall derived inhibitors are generated as byproducts of the process. It is essential to apply a detoxification strategy to remove the toxic inhibitors from hemicellulosic hydrolysates. This allows for a satisfactory xylitol yield and productive microbial fermentation. During detoxification, several methods such as calcium hydroxide overliming, activated charcoal, and ion-exchange are routinely used to overcome the inhibitors. More recently, biological applications (laccase, direct implication of microorganisms having the affinity towards inhibitors) and systems biology-based approaches have gained significant attraction for the development of microbial traits to counteract the effects of inhibitors while simultaneously fermenting the xylose sugar solution into xylitol. This chapter aims to discuss the various strategies used in the detoxification of lignocellulose hydrolysates for the fermentative production of xylitol. Particular emphasis is placed on the biological applications used for clarification of hemicellulosic syrups with future perspectives.