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Co-production systems are a strategy used to diversify production chains and to enable more profitable processes. In addition, the valorization of the sugar-and-alcohol industry through by-product conversion into value-added products is environmentally friendly and enhances their competitiveness to other products available in the market. Thus, the aim of the current study is to evaluate xylitol and ethanol co-production by Candida tropicalis deriving from sugarcane by-products, such as bagasse and straw, supplemented with molasses. Sugarcane bagasse and straw hemicellulosic hydrolysate was obtained through dilute-acid hydrolysis with H2SO4; next, it was concentrated and detoxified with activated charcoal. Different commercial sucrose concentrations (5, 25 and 50 gL−1) were added to the bagasse and straw hemicellulosic hydrolysate in semi-defined medium. In addition, hydrolysate supplementation with sugarcane molasses was evaluated based on sucrose content (10 and 50 gL−1) adjustment. Batch fermentations were carried out in 125-mL Erlenmeyer flasks filled with 50 mL of medium, at 30 °C, 200 rpm, pH 5.5, for 48 h. Molasses supplementation adjusted to 50 gL−1 sucrose in sugarcane bagasse and straw hemicellulosic hydrolysate recorded the maximum xylitol (30.61 gL−1) and ethanol (47.97 gL−1) concentrations observed in the current study. Besides, volumetric xylitol (0.64 gL−1h−1) and ethanol (1.00 gL−1h−1) productivity was observed under the very same condition. Results have shown the likelihood of co-producing xylitol and ethanol through C. tropicalis by using sugarcane by-products to compose the fermentation medium as strategy to intensify and integrate these bioprocesses in sugarcane biorefineries.

Xylitol and sorbitol are high-added-value chemicals with important applications in the food and pharmaceutical industries, since they present a sweetness similar to that of sucrose with lower caloric content and glycemic index, insulin-independent metabolism, and microbiological and chemical stability. The market focused on these polyols has been continuously growing due to their relevant properties and to the likelihood of using them as platform chemicals. Nowadays, they are produced at the commercial scale based on chemical routes that still present significant efficiency and sustainability issues, a fact that has encouraged research focusing on the development of biotechnological routes based on using productive chain by-products, mainly lignocellulosic and starchy biomasses, as raw material. It has been suggested that integrating xylitol and sorbitol production to biorefineries would contribute to the technical and economic feasibility of these productive units. The aim of the current chapter is to explore chemical and biotechnological routes for xylitol and sorbitol production, their applications and market trends, as well as challenges and opportunities for the incorporation of these important polyols into biorefineries.

Xylitol is a GRAS (Generally Recognized as Safe) polyol commonly used in the food industry and able to promote several benefits to the health. In addition, it can also be used as a building block molecule for the manufacture of different high-value chemicals. Currently, the commercial production of xylitol occurs by chemical route through the catalytic hydrogenation of xylose from lignocellulosic biomass. Since this is an expensive process due to the severe reactional conditions employed, the biotechnological route for xylitol production, which comprises the biological conversion of xylose into xylitol, emerges as a potential lower-cost alternative to obtain this polyol due to the milder process conditions required. However, the biotechnological route still presents important bottlenecks and challenges that impairs the process scaling up. Modern strategies and technologies that can potentially improve xylitol bioproduction include adaptive evolution of microbial strains to enhance their tolerance to inhibitors and the xylose uptake rate during the fermentation step; development of engineered microorganisms to result in higher xylose-to-xylitol bioconversion yields; as well as xylitol purification techniques to improve the recovery yields. Moreover, techno-economic analysis of the overall production chain is essential to identify the process viability for large-scale implementation as well as the steps requiring improvements. These are some key factors discussed in this review, which aims to provide insights for the development of a more economically competitive, less energy demanding and scalable new technology for xylitol production.

Biorefinery occupies a major domain in modern bioeconomy. It offers several promising opportunities to replace fossil resources-based products and fuels in a sustainable manner paving the way to establish a carbon-neutral economy. Currently, biobased chemicals and polymers production is approximately 50 million tones. One of the major bottlenecks in biorefinery-based operation is the economical production of second-generation (2G) sugars, which serves as a building block in a renewable economy. Besides 2G ethanol and other bioenergy products, high commercial value-based chemicals, such as organic acids, polymers, sugar alcohols, amino acids, enzymes, antibiotics, among others, can be produced from 2G sugars via fermentation or chemical methods. In the long haul, economic competitiveness and sustainability of biorefineries depend on the processes integration and intensification, market flexibility, and continuous innovation for the development of new products. Furthermore, a reliable supply chain for regular and sufficient feedstock at stable price and partnerships in each step with external players are necessary. This chapter discusses the basic principles and key aspects of modern bioeconomy. Special attention is given to the role of biorefinery in bioeconomy and the current technological status of some important biochemicals.

Sweeteners are functional food additives used prominently in food and beverages since a long time. Artificial sweeteners or non-nutritive sweeteners are sugar free substitutes to conventional sugars and have a major share in total sweeteners demand. Recently, some new artificial sweeteners such as acesulfame, aspartame, cyclamate, saccharin and sucralose have been accepted by society largely despite having different views on their contribution in energy balance on human health. Sugar polyols such as xylitol, sorbitol, erythritol, and mannitol are most common artificial sweeteners which are in vogue and have unique sweetness properties with low calories contribution. The global market of sweeteners in 2010 was 9 million US$ which is expected to grow with the compound annual growth rate of approximately of 3% by 2022. Due to significant developments in last 3 or 4 decades in biomass conversion via biotechnological and chemicals methods, desired level of recovery of sugar alcohols can be obtained. Microbial production of artificial sweeteners by improved fermentation methods using economic carbon and nitrogen source can cater the increased demand. Modern genetic engineering approaches using novel methods such as CRISPR/Cas9 and rational strain engineering, adaptive laboratory evolution and high-throughput screening approaches may play a pivotal role for the economic production of artificial sweeteners. This chapter presents the classification of sweeteners, commercial outlook and demand of sweeteners, health effects and regulations for sweeteners consumption. Microbial production of sugar alcohols is reviewed as a biotechnological process model applied in the sweeteners segment.