cellulose polymer, also the pretreatment methods separate the lignin and hemicelluloses in the cell wall. Many of the bonds breakdown by the hydrolysate components
application and also the carbohydrates become chemically modified, the components
used for the pretreatment include various methods such as the ionic compounds,
milling, and Organosolv (George et al. 2015; Han et al. 2015; Narron et al. 2016).
In high severe environments, the applied pretreatment features show great commercial level advantages. It is also depicted that along with applications also keep an
eye on the disadvantages (George et al. 2015; Han et al. 2015; Narron et al. 2016).
Hereby understood that this pretreatment effectively eliminates the lignin components from the cell wall. Chemicals such as alkali and other acids are used for the
pretreatment methods for the modification of cell wall (components, i.e., degradation
of pentoses along with the breakdown of several chemical components in the cell
wall) (Ji et al. 2016; Lima et al. 2014). These modifications lead to the wide
applications in industrial as well in commercial companies, i.e., fermentation processes and in many enzymatic hydrolysis that yield efficiently and greatly promotes
product yield (Rasmussen et al. 2014).
All the pretreatment methods are accompanied by the production of certain
inhibitors formation from the above-mentioned polymers (lignin, cellulose, and
hemicellulose). The inhibitors that are produced as a result of pretreatment include:
HMF, furfurals, week acids, and phenolic compounds (Jacobsen and Wyman 2000).
These microbial inhibitors are the main challenge to bioethanol production.
Some of the pretreatment strategies, their modes of actions on lignocellulosic
biomass and presence or absence of inhibitor formation are summarized in Table 5.2
(Abraham et al. 2020; Harmsen et al. 2010; Ravindran and Jaiswal 2016).
5.3 Hydroxymethyl Furfural (HMF)
Common pretreatment techniques (e.g., steam and acid) seem to produce microbial
inhibitors, these inhibitors may include 5HMF (5-hydroxymethylfurfural) and furfural, released into the hydrolysate and acting in the reduction of bioethanol yield,
through the fermenting yeast inhibition (Crigler et al. 2020).
HMF and furfural are released by the loss of water molecules from sugar either in
high temperature or acidic environments; HMF comes from hexose sugars and
furfural comes from pentose sugar. It is not understood that these inhibitors inhibit
the cells, but the enzymes responsible for fermentation and glycolysis are known to
be inhibited, with the induction of reactive oxygen, and a decrease in the population
of reduced redox cofactors (Crigler et al. 2020). HMF tends to negatively affect the
metabolism of yeast and prolong the process of ethanol production (by fermentation)
(Sukwong et al. 2019). Chemical structure of HMF is depicted in Fig. 5.8
(Menegazzo et al. 2018).
Production of HMF is easy by losing three molecules of water from hexose
material, in a reaction catalyzed by acid. But HMF synthesis is not that simple, but
complicated as it involves many other reactions.
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FaizaKausar et al.
application and also the carbohydrates become chemically modified, the components
used for the pretreatment include various methods such as the ionic compounds,
milling, and Organosolv (George et al. 2015; Han et al. 2015; Narron et al. 2016).
In high severe environments, the applied pretreatment features show great commercial level advantages. It is also depicted that along with applications also keep an
eye on the disadvantages (George et al. 2015; Han et al. 2015; Narron et al. 2016).
Hereby understood that this pretreatment effectively eliminates the lignin components from the cell wall. Chemicals such as alkali and other acids are used for the
pretreatment methods for the modification of cell wall (components, i.e., degradation
of pentoses along with the breakdown of several chemical components in the cell
wall) (Ji et al. 2016; Lima et al. 2014). These modifications lead to the wide
applications in industrial as well in commercial companies, i.e., fermentation processes and in many enzymatic hydrolysis that yield efficiently and greatly promotes
product yield (Rasmussen et al. 2014).
All the pretreatment methods are accompanied by the production of certain
inhibitors formation from the above-mentioned polymers (lignin, cellulose, and
hemicellulose). The inhibitors that are produced as a result of pretreatment include:
HMF, furfurals, week acids, and phenolic compounds (Jacobsen and Wyman 2000).
These microbial inhibitors are the main challenge to bioethanol production.
Some of the pretreatment strategies, their modes of actions on lignocellulosic
biomass and presence or absence of inhibitor formation are summarized in Table 5.2
(Abraham et al. 2020; Harmsen et al. 2010; Ravindran and Jaiswal 2016).
5.3 Hydroxymethyl Furfural (HMF)
Common pretreatment techniques (e.g., steam and acid) seem to produce microbial
inhibitors, these inhibitors may include 5HMF (5-hydroxymethylfurfural) and furfural, released into the hydrolysate and acting in the reduction of bioethanol yield,
through the fermenting yeast inhibition (Crigler et al. 2020).
HMF and furfural are released by the loss of water molecules from sugar either in
high temperature or acidic environments; HMF comes from hexose sugars and
furfural comes from pentose sugar. It is not understood that these inhibitors inhibit
the cells, but the enzymes responsible for fermentation and glycolysis are known to
be inhibited, with the induction of reactive oxygen, and a decrease in the population
of reduced redox cofactors (Crigler et al. 2020). HMF tends to negatively affect the
metabolism of yeast and prolong the process of ethanol production (by fermentation)
(Sukwong et al. 2019). Chemical structure of HMF is depicted in Fig. 5.8
(Menegazzo et al. 2018).
Production of HMF is easy by losing three molecules of water from hexose
material, in a reaction catalyzed by acid. But HMF synthesis is not that simple, but
complicated as it involves many other reactions.
134
FaizaKausar et al.