Chapter 1 - Conversion of lignocellulosic biomass to xylitol and its applications

Abstract

In the 1930s, interest in commercializing xylitol as a sweetener began due to a shortage of sugar during World War II. Xylitol production started in Finland in the 1970s, after the development of mass-scale production of D-xylose by chromatographic separation of several woody hemicelluloses. After several studies evaluated the effectiveness of xylitol in reducing dental plaque in 1970, xylitol was widely researched and accepted globally as a natural sweetener approved by the US Food and Drug Administration (FDA). More than 35 countries have approved the use of xylitol in food, pharmaceuticals, and health products, mainly in chewing gums, toothpastes, syrups, and confectionery. Regular xylitol consumption was defined as 5–7 g daily, making it ideal to ingest at least three times a day for human adults. In addition, it can be used clinically as a sugar substitute for diabetics. Xylitol is considered a “sugar-free” sweetener; it is the sweetest of polyols, being equivalent to sucrose in sweetness, but with fewer calories and a lower glycemic index. Its consumption causes effects of satiety, low glycemic response, and improved nutritional profile. Xylitol production is based mainly on chemical and enzymatic processes. However, each process has its advantages and disadvantages. Currently, the largest commercial production of xylitol is carried out chemically at elevated temperature and pressure. The disadvantage of this process is the low yield with high cost, in addition to some problems related to pollution that are associated with chemical processes. The sustainable alternative route to produce xylitol under environmental reaction conditions is through a biotechnological approach involving xylose reductase (XR). Biotechnological conversion routes provide many opportunities for intensifying the process, therefore, increasing the competitiveness of biorefineries. The biotechnological process for obtaining xylitol has been presented for several reasons; it is an excellent alternative to the conventional chemical method, because in addition to dispensing with the initial purification of xylose (converted into xylitol in the hydrolyzate itself), it can use specific enzymes or microorganisms, which act only in converting xylose to xylitol. Among the raw materials used in the production of xylitol, there are residues from food crops such as sugarcane bagasse, rice husks, wheat straw, cocoa bark and even wood crops such as eucalyptus and cashew bagasse.