A shikimate pathway intermediate (3-dehydroshikimate) has been converted to
vanillin in a multi-step conversion through heterologous expression of four genes
from Podospora pauciseta, Nocardia iowensis, Corynebacterium glutamicum and
Homo sapiens. Brochado et al. (2010) used genome-scale metabolic modelling to
identify gene deletion targets in S. cerevisiae in order to improve vanillin production.
The deletion of genes PDC1 and GDH1 resulted in a fivefold increase in production
of vanillin.
7.3.2.11 Process of Solid-State/Submerged Fermentation
for Production of Aroma Compounds
The process of solid-state fermentation (SSF) is used in the production of biologically active secondary metabolites, which can also be used for the bioflavours
(Prabhakar et al. 2005; Singhania et al. 2009; Ray and Behera 2011). SSF is a
three-phase system, a gas phase (also called headspace), a solid phase and a liquid
phase, which is in the form of a thin layer of moisture, around the solid phase. In
SSF, the microorganism grows on this layer of moisture in the absence or near
absence of free water (Thomas et al. 2013), whereas submerged fermentation (SmF)
involves submersion of the microorganism in an aqueous solution containing all the
nutrients needed for growth. SmF utilizes free flowing liquid substrates, such as
molasses and broths. The bioactive compounds are secreted into the fermentation
broth (Subramaniyam and Vimala 2012). SmF has also been used for the production
of aroma compounds by using several microorganisms. A higher yield is obtained in
SSF as compared to submerged fermentation. In addition, SSF has lower production
costs, lower demand for energy and water as well as less amount of liquid wastes are
produced (Rodríguez and Sanromán 2006; Singhania et al. 2009; Soccol et al. 2017).
The disadvantage of SSF over the SmF is the difficulty in monitoring of process
variables such as pH, moisture and nutrient availability. In the scaling-up, there is
also a problem of heat mass transfer associated with the use of solid substrates
(Pandey 2003; Soccol et al. 2017). The application of SSF in large scale is limited
(Singhania et al. 2010; Salihu and Alam 2012) as the aroma compounds are either
produced in the solid matrix or in the headspace which can be lost or stripped when
aeration is required (Try et al. 2018).
Rossi (2009) have used the fungi Ceratocystis fimbriata for the production of a
variety of aromas using citric pulp (CP), a waste from the citric juice production
industry as the substrate for fermentation. Other materials such as carbon sources
(sugarcane molasses, soya molasses) and nitrogenous sources (soya bran or urea)
were also checked for the production of aromatic compounds. Gas chromatography
of the headspace showed the best production of volatile compounds (99.60 μmol/L
g), when the citric pulp was supplemented with 50% of soya bran, 25% of sugarcane
molasses and mineral saline solution. The production of a number of fruity esters,
namely isoamyl acetate, phenylethyl acetate, ethyl dodecanoate, decanoate and
octanoate from orange peel, has also been reported by Mantzouridou et al. (2015).
The solids derived from coffee such as coffee pulp and coffee husk can also be
used for the production of flavour compounds (Pandey et al. 2000). Ceratocystis
fimbriata was grown in two media constituted from steam treated coffee husk
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T. Malik and S. Rawat
vanillin in a multi-step conversion through heterologous expression of four genes
from Podospora pauciseta, Nocardia iowensis, Corynebacterium glutamicum and
Homo sapiens. Brochado et al. (2010) used genome-scale metabolic modelling to
identify gene deletion targets in S. cerevisiae in order to improve vanillin production.
The deletion of genes PDC1 and GDH1 resulted in a fivefold increase in production
of vanillin.
7.3.2.11 Process of Solid-State/Submerged Fermentation
for Production of Aroma Compounds
The process of solid-state fermentation (SSF) is used in the production of biologically active secondary metabolites, which can also be used for the bioflavours
(Prabhakar et al. 2005; Singhania et al. 2009; Ray and Behera 2011). SSF is a
three-phase system, a gas phase (also called headspace), a solid phase and a liquid
phase, which is in the form of a thin layer of moisture, around the solid phase. In
SSF, the microorganism grows on this layer of moisture in the absence or near
absence of free water (Thomas et al. 2013), whereas submerged fermentation (SmF)
involves submersion of the microorganism in an aqueous solution containing all the
nutrients needed for growth. SmF utilizes free flowing liquid substrates, such as
molasses and broths. The bioactive compounds are secreted into the fermentation
broth (Subramaniyam and Vimala 2012). SmF has also been used for the production
of aroma compounds by using several microorganisms. A higher yield is obtained in
SSF as compared to submerged fermentation. In addition, SSF has lower production
costs, lower demand for energy and water as well as less amount of liquid wastes are
produced (Rodríguez and Sanromán 2006; Singhania et al. 2009; Soccol et al. 2017).
The disadvantage of SSF over the SmF is the difficulty in monitoring of process
variables such as pH, moisture and nutrient availability. In the scaling-up, there is
also a problem of heat mass transfer associated with the use of solid substrates
(Pandey 2003; Soccol et al. 2017). The application of SSF in large scale is limited
(Singhania et al. 2010; Salihu and Alam 2012) as the aroma compounds are either
produced in the solid matrix or in the headspace which can be lost or stripped when
aeration is required (Try et al. 2018).
Rossi (2009) have used the fungi Ceratocystis fimbriata for the production of a
variety of aromas using citric pulp (CP), a waste from the citric juice production
industry as the substrate for fermentation. Other materials such as carbon sources
(sugarcane molasses, soya molasses) and nitrogenous sources (soya bran or urea)
were also checked for the production of aromatic compounds. Gas chromatography
of the headspace showed the best production of volatile compounds (99.60 μmol/L
g), when the citric pulp was supplemented with 50% of soya bran, 25% of sugarcane
molasses and mineral saline solution. The production of a number of fruity esters,
namely isoamyl acetate, phenylethyl acetate, ethyl dodecanoate, decanoate and
octanoate from orange peel, has also been reported by Mantzouridou et al. (2015).
The solids derived from coffee such as coffee pulp and coffee husk can also be
used for the production of flavour compounds (Pandey et al. 2000). Ceratocystis
fimbriata was grown in two media constituted from steam treated coffee husk
148
T. Malik and S. Rawat