accumulation of anions thus lipid-soluble acids move across the membrane and
dissociate in the cytoplasm resulting in the pH lowering. This acidity causes
suppression of phosphogluconate pathway, enhanced turgor pressure, aggregation
of proteins, oxidative stress, lipid peroxidation, and plasm and vacuolar membrane
disruption which affects the trafficking across membranes and leads to the ultimate
cessation of cell (Brandt et al. 2019).
During the fermentation process, the lag phase is short, i.e., almost 4 h, which
shows the adaptation of yeast cells to the spiked broth which allows them for normal
development for the fermentation process. The inhibitory compounds are more
actively present in the lag phase for obtaining greater contact with yeast cells.
Moreover, it is concluded that the small amount of inhibitory acids is somehow
beneficial for ethanol production (fermentation itself), as it will be playing the role of
catalyst for the provision of energy needed for the ATP production. On the other
hand, higher concentrations of acids will cause a decrease in pH, therefore affecting
the fermentation and leading to cell lysis (De Klerk et al. 2018).
5.6 Phenolic Compounds
When side chains of phenylpropanes are cleaved oxidatively it leads to phenolic
acids, e.g., vanillic acids, 4-hydroxyphenolic, and syringic acids, structure of
syringic acid and benzoic acid are shown in Fig. 5.12 (Liu et al. 2020). These
compounds have been found to come from lignin or the hydrolytic reactions of
esterified phenols, this fact is supported by the presence of syringyl, guaiacyl, and
4-hydroxyphenyl (Jönsson and Martín 2016).
In the pretreatment of eucalyptus green liquor for ethanol production, the inhibitory compounds produced were syringic acid, syringaldehyde, vanillin, and
acetosyringone. These inhibitors were observed to affect the metabolic pathways
COOH
Benzoic Acid
O
OH
O
Syringic Acid
Fig. 5.12 Phenolic acids (Liu et al. 2020)
5 Challenges in Bioethanol Production: Effect of Inhibitory Compounds
139
dissociate in the cytoplasm resulting in the pH lowering. This acidity causes
suppression of phosphogluconate pathway, enhanced turgor pressure, aggregation
of proteins, oxidative stress, lipid peroxidation, and plasm and vacuolar membrane
disruption which affects the trafficking across membranes and leads to the ultimate
cessation of cell (Brandt et al. 2019).
During the fermentation process, the lag phase is short, i.e., almost 4 h, which
shows the adaptation of yeast cells to the spiked broth which allows them for normal
development for the fermentation process. The inhibitory compounds are more
actively present in the lag phase for obtaining greater contact with yeast cells.
Moreover, it is concluded that the small amount of inhibitory acids is somehow
beneficial for ethanol production (fermentation itself), as it will be playing the role of
catalyst for the provision of energy needed for the ATP production. On the other
hand, higher concentrations of acids will cause a decrease in pH, therefore affecting
the fermentation and leading to cell lysis (De Klerk et al. 2018).
5.6 Phenolic Compounds
When side chains of phenylpropanes are cleaved oxidatively it leads to phenolic
acids, e.g., vanillic acids, 4-hydroxyphenolic, and syringic acids, structure of
syringic acid and benzoic acid are shown in Fig. 5.12 (Liu et al. 2020). These
compounds have been found to come from lignin or the hydrolytic reactions of
esterified phenols, this fact is supported by the presence of syringyl, guaiacyl, and
4-hydroxyphenyl (Jönsson and Martín 2016).
In the pretreatment of eucalyptus green liquor for ethanol production, the inhibitory compounds produced were syringic acid, syringaldehyde, vanillin, and
acetosyringone. These inhibitors were observed to affect the metabolic pathways
COOH
Benzoic Acid
O
OH
O
Syringic Acid
Fig. 5.12 Phenolic acids (Liu et al. 2020)
5 Challenges in Bioethanol Production: Effect of Inhibitory Compounds
139