Thais Suzane dos Santos Milessi

Bioconversion of sugarcane biomass into ethanol: an overview about composition, pretreatment methods, detoxification of hydrolysates, enzymatic saccharification, and ethanol fermentation.

Depleted supplies of fossil fuel, regular price hikes of gasoline, and environmental damage have necessitated the search for economic and eco-benign alternative of gasoline. Ethanol is produced from food/feed-based substrates (grains, sugars, and molasses), and its application as an energy source does not seem fit for long term due to the increasing fuel, food, feed, and other needs. These concerns have enforced to explore the alternative means of cost competitive and sustainable supply of biofuel. Sugarcane residues, sugarcane bagasse (SB), and straw (SS) could be the ideal feedstock for the second-generation (2G) ethanol production. These raw materials are rich in carbohydrates and renewable and do not compete with food/feed demands. However, the efficient bioconversion of SB/SS (efficient pretreatment technology, depolymerization of cellulose, and fermentation of released sugars) remains challenging to commercialize the cellulosic ethanol. Among the technological challenges, robust pretreatment and development of efficient bioconversion process (implicating suitable ethanol producing strains converting pentose and hexose sugars) have a key role to play. This paper aims to review the compositional profile of SB and SS, pretreatment methods of cane biomass, detoxification methods for the purification of hydrolysates, enzymatic hydrolysis, and the fermentation of released sugars for ethanol production.

Dilute Acid Hydrolysis of Agro-Residues for the Depolymerization of Hemicellulose: State-of-the-Art

Geo-political, long-term economic and sustainable concerns are promoting researchers and entrepreneurs to harness the potential of lignocellulosic feedstock (LCF) into industrially significant products. Agro-residues (sugarcane bagasse, wheat straw, rice straw, corn stover, etc.) constitute the principal fraction of LCF and are available in large amounts globally. The judicious exploration of agro-residues into important products such as d-xylitol, an artificial sweetener, may provide a strong platform for its sustainable supply to the medical and non-medical applications-based sectors. Pretreatment of agro-residues by dilute acid hydrolysis is an inevitable process for the depolymerisation of hemicellulosic fraction into xylose and other sugars. Dilute acid catalyses hemicellulose fractionation at high temperature within short reaction times. Significant developments have been made in the past towards the chemical hydrolysis of agro-residues, particularly for the hemicellulose breakdown. Critical parameters such as acid load, temperature, residence time and solid-to-liquid ratio play pivotal roles in the kinetics of dilute acid hydrolysis of agro-residues. Furthermore, reactor configurations such as counter-current, plug-flow, percolation and shrinking-bed have been designed in order to maximize the sugars recovery with minimum inhibitors generation. This chapter reviews the process parameters, kinetics, methods and reactor engineering for the dilute acid catalysed processes employed for agro-residues.

Bioethanol Production from Sugarcane Bagasse by a Novel Brazilian Pentose Fermenting Yeast Scheffersomyces shehatae UFMG-HM 52.2: Evaluation of Fermentation Medium

Bioconversion of hemicellulosic sugars into second generation (2G) ethanol plays a pivotal role in the overall success of biorefineries. In this study, ethanol production performance of a novel xylose-fermenting yeast, Scheffersomyces shehatae UFMG-HM 52.2, was evaluated under batch fermentation conditions using sugarcane bagasse (SB) hemicellulosic hydrolysate as carbon source. Dilute acid hydrolysis of SB was performed to obtain sugarcane bagasse hemicellulosic hydrolysate (SBHH). It was concentrated, detoxified, and supplemented with nutrients in different formulations to prepare the fermentation medium to the yeast evaluation performance. S. shehatae UFMG-HM 52.2 (isolated from Brazilian Atlantic rain forest ecosystem) was used in fermentations carried out in Erlenmeyer flasks maintained in a rotator shaker at 30°C and 200 rpm for 72 h. The use of a fermentation medium composed of SBHH supplemented with 5 g/L ammonium sulfate, 3 g/L yeast extract, and 3 g/L malt extract resulted in 0.38 g/g of ethanol yield and 0.19 g L.h of volumetric productivity after 48 h of incubation time.

Bioconversion of Hemicellulose from Sugarcane Biomass Into Sustainable Products

During the processing of sugarcane, the sugarcane straw (SS) is remained on field and do not presents suitable use. After the juice extraction from sugarcane stem, the fraction that is left over is called sugarcane bagasse (SB) [3]. Both residues (SB and SS) represent a sizeable fraction of agro-residues collected annually. The annual world production of sugarcane is ∼1.6 billion tons, which yields approximately 279 million metric tons (MMT) of SB and SS [1, 4].

Hemicellulosic ethanol production by immobilized cells of Scheffersomyces stipitis: Effect of cell concentration and stirring

Bioconversion of hemicellulosic hydrolysate into ethanol plays a pivotal role in the overall success of biorefineries. For the efficient fermentative conversion of hemicellulosic hydrolysates into ethanol, the use of immobilized cells system could provide the enhanced ethanol productivities with significant time savings. Here, we investigated the effect of 2 important factors (e.g., cell concentration and stirring) on ethanol production from sugarcane bagasse hydrolysate using the yeast Scheffersomyces stipitis immobilized in calcium alginate matrix. A 22 full factorial design of experiment was performed considering the process variables- immobilized cell concentration (3.0, 6.5 and 10.0 g/L) and stirring (100, 200 and 300 rpm). Statistical analysis showed that stirring has the major influence on ethanol production. Maximum ethanol production (8.90 g/l) with ethanol yield (Yp/s) of 0.33 g/g and ethanol productivity (Qp) of 0.185 g/l/h was obtained under the optimized process conditions (10.0 g/L of cells and 100 rpm).

Immobilization of Scheffersomyces stipitis cells with calcium alginate beads: A sustainable method for hemicellulosic ethanol production from sugarcane bagasse hydrolysate

Abstract Lignocellulosic ethanol has shown promising alternative to gasoline however expensive and cumbersome bioprocessing limits the commercialization of biofuels. The major impediment toward the economic ethanol production is the bioconversion of sugars into ethanol via microbial fermentation. Application of immobilized cells in fermentation of hemicellulosic hydrolysate could minimize the ethanol production cost. This study evaluated the conditions for cell immobilization for the yeast Scheffersomyces stipitis NRRL Y-7124 by the method of entrapment in calcium alginate gel. A full factorial design (23) was designed to investigate the effect of three process variables i.e. sodium alginate concentration (1.0, 1.5 and 2.0%), calcium chloride concentration (0.1, 0.15 and 0.2 M) and conditioning time (12, 18 and 24 h). Twelve numbers of experiments were performed with central points in quadruplicates. The range of ethanol production in all experiments was observed from 4.88 g/L (Yp/s, 0.16 g/g) to 9.9 g/L ethanol (Yp/s, 0.29 g/g). Statistical analysis revealed that immobilization conditions (2.0% sodium alginate concentration, 0.1M calcium chloride concentration and 12 h conditioning time) were responsible for high stability of immobilized cells which in-turn enabled the maximum ethanol production (7.2 g/L, Yp/s, 0.26 g/g) from hemicellulosic hydrolysate of sugarcane bagasse

Biotechnological Production of Xylitol from Biomass

Xylitol is a polyol of interest to food, dental and pharmaceutical industries because of its favorable characteristics such as sweetening capacity, insulin-independent metabolism effects and its lack of carcinogenic properties. It is usually produced by chemical processes that are expensive due to their high energy consumption and many purification steps. Biotechnological routes are promising because they can be carried out using mild conditions and have the possibility of using hydrolysates from renewable sources as raw materials without the need of extensive purification of xylose before the fermentation step. Different lignocellulosic materials have been studied as alternative raw materials in the fermentative process for xylitol production. However, the structure of lignocellulose is recalcitrant and a pretreatment step is necessary to release monomeric sugars that does not form compounds toxic to microorganisms. Another challenge for xylitol production by fermentation is the identification of efficient microorganisms for converting the pentose sugars present in hemicellulosic hydrolysates. Different strategies have also been investigated, aiming to optimize the biotechnological way, such as use of different configurations of bioreactors, process options and downstream steps. This chapter will explore biotechnological xylitol production from the selection and preparation of the raw material to fermentative process conditions, downstream strategies and future perspectives. These topics will be discussed to offer readers a better understanding of biotechnological routes to xylitol as well as their potential and future prospects.

Biomass Pretreatment With Oxalic Acid for Value-Added Products

Monomeric sugars released from carbohydrate fractions of lignocellulosic materials can be substrates for industrial fermentative processes in order to obtain bioproducts with potential economic and social interest. When diluted acid solutions are used to pretreat biomass, the result is a solid fraction in which cellulose is more accessible to hydrolytic enzymes and a liquid fraction enriched in sugars (mainly pentoses) from hemicellulose. Pretreatment with dilute oxalic acid is a promising approach, resulting in high efficiency in hemicellulose hydrolysis, which generates a lower quantity of compounds toxic to microbial metabolism. In addition, once this acid is organic, it can be recovered by usual techniques and reused in a pretreatment step. Within this context, this chapter presents the use of oxalic acid pretreatment for different biomasses, including the structural changes that occur after using this method as well as applications of the obtained solid and liquid fraction in fermentative processes.