Tree Genetics and Molecular Breeding 2024, Vol.14, No.5, 247-255 http://genbreedpublisher.com/index.php/tgmb 249 3 Technological Aspects of Agave Bioethanol Production 3.1 Pre-treatment processes Pre-treatment is a crucial step in the bioethanol production process from lignocellulosic biomass, including Agave. Various methods such as chemical, physical, and biological pre-treatments are employed to break down the complex structure of lignocellulosic biomass, making the cellulose and hemicellulose more accessible for enzymatic hydrolysis (Figure 1). Chemical methods include acid and alkali treatments, which are effective in removing lignin and hemicellulose, thus enhancing the digestibility of cellulose (Moodley et al., 2020; Rezania et al., 2020; Das et al., 2021). Physical methods like steam explosion and ammonia fiber expansion (AFEX) are also used to disrupt the biomass structure (Flores-Gómez et al., 2018; Zhao et al., 2021). Biological methods involve the use of microorganisms or enzymes to degrade lignin and hemicellulose (Muthuvelu et al., 2019; Malik et al., 2021). Figure 1Agave tequilanaandSalmianaplants and its main fractions (Adopted from Flores-Gómez et al., 2018) Image caption: A. tequilana plant (a) and its harvested stem “piña” and leaves (a-c), leaf fiber matter (d, e), the stem-processed tequila residue “bagasse” (f, g). A. salmiana plant (h), A. salmiana leaves (h-j), stems (k, l), its leaf fiber matter (m, n), and the stem-processed Mezcal residue: A. salmiana“bagasse” (o, p) (Adopted from Flores-Gómez et al., 2018) The primary challenge in pre-treating Agave biomass lies in its recalcitrant lignocellulosic structure, which is resistant to enzymatic breakdown. Lignin, a complex aromatic polymer, acts as a physical barrier, protecting cellulose and hemicellulose from enzymatic attack. This necessitates the use of effective pre-treatment methods to break down lignin and expose the polysaccharides (Das et al., 2021; Broda et al., 2022). Additionally, the presence of inhibitory compounds released during pre-treatment can hinder subsequent fermentation processes, posing another significant challenge (Flores-Gómez et al., 2018; Solarte-Toro et al., 2019). 3.2 Fermentation techniques Optimizing the fermentation process is essential to maximize ethanol yield fromAgave sugars. Factors such as pH, temperature, nutrient supplementation, and fermentation time need to be carefully controlled. The use of optimized commercial enzyme cocktails has been shown to enhance sugar conversion rates significantly (Flores-Gómez et al., 2018). Additionally, employing co-fermentation techniques, where multiple microbial strains are used, can improve the efficiency of sugar utilization and ethanol production (Malik et al., 2021). Various microbial strains are employed in the fermentation of Agave biomass. Saccharomyces cerevisiae is the most commonly used yeast due to its high ethanol tolerance and efficient sugar conversion capabilities (Flores-Gómez et al., 2018; Malik et al., 2021). Other strains, such as Pachysolen tannophilus, are also used for
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