the bioreactor in order to keep both nutrient levels and the growth rate maintained at
a predefined value. When the bioreactor operates in the continuous manner fresh
media is introduced and the product is also removed continuously. For example, a
nylon-immobilized lipase from C. cylindracea in batch continuous-flow reactors has
been used for the synthesis of ethyl propionate, isoamyl propionate and isoamyl
butyrate in the continuous mode (Carta et al. 1991). Amyl caprylate has been
synthesized using fluidized bed reactor inoculated with C. rugosa lipase
immobilized on Sepabeads in both batch and continuous mode (Saponjic et al.
2010).
In situ removal process (ISPR) follows the production of the aromatic chemical
by fermentation. On the basis of the physico-chemical properties of the target aroma
product, a particular ISPR method can be followed involving the extraction, immobilization, evaporation, permeation. In addition, bioreactor/separation units are
configured accordingly and also operated under the suitable conditions (Stark and
Stock 2003). Červeňansky et al. (2018) designed a hybrid system for biocatalytic
synthesis of 2-phenylethanol (2PE). Being toxic to the production strain, PE was
continually removed from the fermentation broth using a membrane separation in a
hybrid system consisting of a batch bioreactor and an extractive membrane module,
which prolonged the production cycle and hence the efficiency of the process was
enhanced. The volatile compounds were isolated and concentrated from the matrix
by the processes such as steam distillation/extraction or supercritical CO 2 extraction
or the solid phase microextraction (SPME) (Maarse 1981). Janssens et al. (1989)
reported the stripping of acetate esters from the fermentation broth using the
aeration-air of the fermentation which were then adsorbed on activated coal at the
exhaust of the fermentor, and solvent extraction was used for its subsequent
recovery.
Immobilized cell technology is used to protect microbial cells which are used in
bioflavour production. Immobilization of microbial cells protects the cells from
physico-chemical changes, inhibitory substances and contaminations. It also
enhances substrate utilization, rapid fermentation rates and stability of the product
(Nedović et al. 2016). In the processes of bioflavour production, the most widely
used immobilization technique is the entrapment of cells within porous polymeric
matrices and adsorption on various support materials. The carrier used in the
immobilization process is important as it can affect and also control the flavour
profile of the final product. The factors which determine the choice of the carriers are
viz., its specific requirement, conditions for maintenance of immobilized cell viability and metabolic activity, cost effectiveness, ease of handling, adherence due to
large surface area and presence of functional groups, food grade purity (Kourkoutas
et al. 2010). For example, encapsulation in calcium alginate beads was used to
immobilize Saccharomyces cerevisiae. The immobilized cells showed better growth
performance and also improved de novo synthesis of phenylethyl acetate, ethyl
hexanoate, octanoate, decanoate and dodecanoate. Due to immobilization,
bioflavour production carried out in repeated batch fermentations of orange peel
hydrolysate, was successfully maintained after six consecutive cycles of a total
period of 240 h (Lalou et al. 2013).
7 Biotechnological Interventions for Production of Flavour and Fragrance. . .
151
a predefined value. When the bioreactor operates in the continuous manner fresh
media is introduced and the product is also removed continuously. For example, a
nylon-immobilized lipase from C. cylindracea in batch continuous-flow reactors has
been used for the synthesis of ethyl propionate, isoamyl propionate and isoamyl
butyrate in the continuous mode (Carta et al. 1991). Amyl caprylate has been
synthesized using fluidized bed reactor inoculated with C. rugosa lipase
immobilized on Sepabeads in both batch and continuous mode (Saponjic et al.
2010).
In situ removal process (ISPR) follows the production of the aromatic chemical
by fermentation. On the basis of the physico-chemical properties of the target aroma
product, a particular ISPR method can be followed involving the extraction, immobilization, evaporation, permeation. In addition, bioreactor/separation units are
configured accordingly and also operated under the suitable conditions (Stark and
Stock 2003). Červeňansky et al. (2018) designed a hybrid system for biocatalytic
synthesis of 2-phenylethanol (2PE). Being toxic to the production strain, PE was
continually removed from the fermentation broth using a membrane separation in a
hybrid system consisting of a batch bioreactor and an extractive membrane module,
which prolonged the production cycle and hence the efficiency of the process was
enhanced. The volatile compounds were isolated and concentrated from the matrix
by the processes such as steam distillation/extraction or supercritical CO 2 extraction
or the solid phase microextraction (SPME) (Maarse 1981). Janssens et al. (1989)
reported the stripping of acetate esters from the fermentation broth using the
aeration-air of the fermentation which were then adsorbed on activated coal at the
exhaust of the fermentor, and solvent extraction was used for its subsequent
recovery.
Immobilized cell technology is used to protect microbial cells which are used in
bioflavour production. Immobilization of microbial cells protects the cells from
physico-chemical changes, inhibitory substances and contaminations. It also
enhances substrate utilization, rapid fermentation rates and stability of the product
(Nedović et al. 2016). In the processes of bioflavour production, the most widely
used immobilization technique is the entrapment of cells within porous polymeric
matrices and adsorption on various support materials. The carrier used in the
immobilization process is important as it can affect and also control the flavour
profile of the final product. The factors which determine the choice of the carriers are
viz., its specific requirement, conditions for maintenance of immobilized cell viability and metabolic activity, cost effectiveness, ease of handling, adherence due to
large surface area and presence of functional groups, food grade purity (Kourkoutas
et al. 2010). For example, encapsulation in calcium alginate beads was used to
immobilize Saccharomyces cerevisiae. The immobilized cells showed better growth
performance and also improved de novo synthesis of phenylethyl acetate, ethyl
hexanoate, octanoate, decanoate and dodecanoate. Due to immobilization,
bioflavour production carried out in repeated batch fermentations of orange peel
hydrolysate, was successfully maintained after six consecutive cycles of a total
period of 240 h (Lalou et al. 2013).
7 Biotechnological Interventions for Production of Flavour and Fragrance. . .
151