Bioscience Evidence 2024, Vol.14, No.5, 238-249 http://bioscipublisher.com/index.php/be 239 of various sugars by fermenting organisms, with a focus on both hexose and pentose sugars, highlight the challenges and bottlenecks in the fermentation process, particularly in the context of lignocellulosic biomass conversion, review the recent advancements in metabolic engineering and fermentation strategies that have been developed to improve ethanol yield and productivity, and explore the industrial applications of ethanol fermentation, including its role in biofuel production and other sectors. 2 Historical Background 2.1 Early developments in ethanol production The history of ethanol production is deeply intertwined with the development of human civilization. Alcoholic fermentation is considered one of the oldest biotechnological processes, predating recorded history. The use of yeast, particularly Saccharomyces cerevisiae, has been central to this process. This yeast has been utilized for millennia in the production of alcoholic beverages such as beer and wine, highlighting its cultural and social significance (Carmona-Gutierrez et al., 2012). The fundamental biochemical process involves the conversion of carbohydrates, such as starch or sugar, into alcohol or acid, a method that has been refined over thousands of years to produce consistent and high-quality alcoholic beverages (Maicas, 2021). 2.2 Evolution of fermentation technologies Over time, the technologies and methodologies surrounding fermentation have evolved significantly. Initially, fermentation was a natural process with little control over the variables involved. However, as understanding of the biochemical processes improved, so did the ability to manipulate and optimize these processes. The introduction of specific yeast strains, such as Saccharomyces cerevisiae, and the control of fermentation conditions like temperature and sugar content, have allowed for more predictable and efficient production of ethanol (Maicas, 2021). These advancements have not only improved the quality of alcoholic beverages but have also paved the way for the use of fermentation in other industrial applications, such as biofuel production (Carmona-Gutierrez et al., 2012). 2.3 Transition to industrial-scale production The transition from small-scale, artisanal production to industrial-scale ethanol production marked a significant milestone in the history of fermentation. This shift was driven by the need for large quantities of ethanol, both for alcoholic beverages and as a biofuel. Industrial-scale production requires the optimization of fermentation performance to ensure economic feasibility. This includes addressing challenges such as yeast stress due to high osmotic pressure, pH changes, and the accumulation of fermentation products, which can hinder yeast growth and survival. By improving the tolerance of yeast cells to these stresses, the efficiency of the fermentation process can be significantly enhanced, making large-scale ethanol production more viable and sustainable (Carmona-Gutierrez et al., 2012). 3 Biochemical Pathways of Ethanol Fermentation 3.1 Glycolysis: the initial step Glycolysis is the first step in the ethanol fermentation process, where glucose is broken down into pyruvate. This pathway, known as the Embden-Meyerhof-Parnas (EMP) pathway, involves a series of enzymatic reactions that convert glucose into two molecules of pyruvate, generating a net gain of two ATP molecules and two NADH molecules. In some hyperthermophilic Archaea, such as Pyrococcus furiosus, modifications to the glycolytic pathway have been observed, where the typical intermediate 1,3-bisphosphoglycerate is absent, altering the energy yield and redox balance (Straub et al., 2020). 3.2 Pyruvate decarboxylation to acetaldehyde The decarboxylation of pyruvate to acetaldehyde is catalyzed by the enzyme pyruvate decarboxylase (PDC). This reaction releases one molecule of CO2 and converts pyruvate into acetaldehyde. PDC is a key enzyme in this process and has been studied in various organisms, including thermoacidophilic Archaea, where it exhibits thermostable and oxygen-stable properties, making it suitable for industrial applications (Alharbi et al., 2022). In plants, PDC also plays a crucial role in energy production under anaerobic conditions (Bui et al., 2019) (Figure 1).
RkJQdWJsaXNoZXIy MjQ4ODYzMg==