Journal of Energy Bioscience 2024, Vol.15, No.4, 267-276 http://bioscipublisher.com/index.php/jeb 269 3 Fermentation Processes 3.1 Overview of fermentation in bioethanol production Fermentation is a biochemical process that converts sugars into bioethanol through the action of microorganisms. The basic principles involve the breakdown of complex carbohydrates into simpler sugars, which are then metabolized by microorganisms to produce ethanol and carbon dioxide. The key steps in the fermentation process include substrate preparation, inoculation with a suitable microorganism, fermentation under controlled conditions, and ethanol recovery. Marine microorganisms, such as certain strains of yeast and bacteria, have shown potential in bioethanol production due to their ability to tolerate high salinity and other harsh conditions (Greetham et al., 2018; Turner et al., 2022). 3.2 Fermentation pathways in marine microorganisms Marine microorganisms utilize various fermentation pathways to convert substrates into bioethanol. For instance, the marine flavobacterium Formosa agariphila degrades the algal polysaccharide ulvan into fermentable monosaccharides through a series of enzymatic reactions involving polysaccharide lyases, sulfatases, and glycoside hydrolases (Reisky et al., 2019). Another example is the thermophilic bacterium Geobacillus thermoglucosidasius, which ferments both C5 and C6 sugars via glycolysis, the pentose phosphate pathway, and the TCA cycle, producing ethanol, lactate, acetate, and formate under different growth conditions (Tang et al., 2009). Additionally, marine yeasts like Wickerhamomyces anomalus M15 have been shown to effectively ferment seaweed-derived sugars into ethanol, demonstrating high tolerance to various inhibitors present in the medium (Turner et al., 2022) (Table 1). Table 1 Ethanol productions in fermentations using natural and concentrated semi-synthetic seaweed hydrolysate media (Adopted from Turner et al., 2022) Glucose (g/L) Glucose+galactos e (g/L) Total sugar (g/L) Ethanol (g/L) Yield based on glucose (%) Yield based on glucose + galactose Yield based on total sugar (%) L. digitata YPD 20 20 20 9.8±2.03 95.7 95.7% 95.7 Natural 1.32 1.87 20.14 1.13±0.04 167.2 118.0% 11.0 5x 6.6 9.35 100.7 5.41±0.97 160.1 113.0% 10.5 7.5x 9.9 14.03 151.1 7.87±2.19 155.3 109.6% 10.2 10x 13.2 18.7 201.4 5.79±1.37 85.7 60.5% 5.6 U. linza YPD 20 20 20 10.03±0.52 97.9 97.9% 97.9 Natural 8.16 8.83 16.61 4.26±0.48 102.0 94.2% 50.1 5x 40.8 44.15 83.05 20.43±2.80 97.8 90.4% 48.0 7.5x 61.2 66.23 124.6 34.7±4.40 110.7 102.3% 54.4 10x 81.6 88.3 166.1 45.04±4.40 107.8 99.6% 53.0 P. umbilicalis YPD 20 20 20 10.31±1.36 100.7 100.7% 100.7 Natural 3.52 9.81 13.08 3.39±0.28 188.1 67.5% 50.6 5x 17.6 49.05 65.4 7.49±2.26 83.1 29.8% 22.4 7.5x 26.4 73.58 98.1 13.61±0.37 100.7 36.1% 27.1 10x 35.2 98.1 130.8 19.85±2.64 110.1 39.5% 29.6 3.3 Factors influencing fermentation efficiency Several factors influence the efficiency of the fermentation process in marine microorganisms. Temperature is a critical factor, as many marine microorganisms are thermophilic and exhibit optimal ethanol production at elevated temperatures (Tang et al., 2009; Niu et al., 2015). pH levels also play a significant role, with different microorganisms requiring specific pH ranges for optimal activity. Salinity is another important factor, as marine microorganisms must be able to tolerate high salt concentrations to thrive in seawater-based fermentation
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