Publicação
Strategies for increasing aroma production from castor oil by Yarrowia lipolytica
| Resumo: | The aromatic compounds produced by biotechnological processes are increasingly accepted by consumers because they are considered as “natural” compounds. In addition, they are of great interest due to the high yields obtained comparatively to chemical processes. γ-Decalactone is an aromatic compound of industrial interest, resulting from the peroxisomal β-oxidation of ricinoleic acid. This fatty acid, the major constituent of castor oil, is the precursor most commonly used in the biotechnological production of this aroma. Although there are many works described in the literature about aroma production, several factors remain to be fully understood and optimized in order to improve γ- decalactone production. Thus, this work initially aimed to study the influence of lipase in castor oil hydrolysis and the consequent impact in the aroma production. Lipozyme TL IM® revealed to be an efficient lipase to hydrolyze castor oil (95.4 % of hydrolysis in 48 h). In spite of the higher aroma concentration obtained without lipase, the process was faster when Lipozyme TL IM® was involved, resulting in similar productivities. One of the limitations in the development of an industrial process for γ-decalactone production is the toxicity of the substrate and the lactone. The immobilization by adsorption of Y. lipolytica W29 in methyl polymetacrilate and DupUm® was studied in flasks batch cultures. After selecting the best conditions for cell immobilization, free and immobilized cells were used in the biotransformation of ricinoleic acid into γ-decalactone. The results demonstrated an improvement in γ-decalactone concentration with adsorbed Y. lipolytica cells on DupUM® since a greater amount of γ-decalactone was accumulated in the medium compared to free cells. In this case the use of the extracellular lipase Lipozyme TL IM® in the biotransformation medium was crucial to allow castor oil hydrolysis, without it the substrate access to the cells would be impossible. Furthermore, immobilized cells hold a stable γ- decalactone production after being stored for 30 days at 4 ºC. Also after reuse in three consecutive biotransformations, γ-decalactone concentration was ca. 80 % of that in the first cycle, indicating that immobilized cells could be reused for at least three cycles. The production of γ-decalactone in batch cultures of Y. lipolytica W29 free cells was studied at bioreactor level and the preformance in stirred tank (STR) and airlift bioreactors was compared. The oxygen mass transfer was characterized and the positive influence of kLa on γ-decalactone productivity was demonstrated for both bioreactors. A 2-fold increase in γ-decalactone concentration was achieved in the airlift when compared to STR; but, in this last bioreactor the production rate was higher. Morphological characterization of the yeast cells by image analysis showed that pneumatic agitation causes less impact in the cells morphology than mechanical agitation. A predominance of loose cells and quite irregular structures was observed in the STR. So, the airlift bioreactor presents potential interest for larger scale production, with important cost savings, due to the reduction of power input consumption. Finally, the performance of Y. lipolytica strains with modifications in the lipid metabolism at the β-oxidation pathway (acyl-CoA oxidases) and the triglyceride hydrolysis (LIP2 overexpression) using castor oil as substrate was monitored in the STR bioreactor. Depending on genotype, degradation of γ- decalactone was prevented. Also, a faster initial rate of aroma production was obtained with strain overexpressing LIP2 due to the fast hydrolysis of castor oil and release of ricinoleic acid. Step-wise fedbatch cultures improved γ-decalactone concentration only for MTLY40-2P strain, for which a 1.7-fold increase in γ-decalactone final concentration was achieved. The present work brings new insights on the biotechnological production of γ-decalactone contributing with some different strategies for increasing aroma production leading to a greater γ- decalactone concentration. |
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| Autores principais: | Braga, Adelaide |
| Assunto: | Engenharia e Tecnologia::Engenharia Química |
| Ano: | 2014 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The aromatic compounds produced by biotechnological processes are increasingly accepted by consumers because they are considered as “natural” compounds. In addition, they are of great interest due to the high yields obtained comparatively to chemical processes. γ-Decalactone is an aromatic compound of industrial interest, resulting from the peroxisomal β-oxidation of ricinoleic acid. This fatty acid, the major constituent of castor oil, is the precursor most commonly used in the biotechnological production of this aroma. Although there are many works described in the literature about aroma production, several factors remain to be fully understood and optimized in order to improve γ- decalactone production. Thus, this work initially aimed to study the influence of lipase in castor oil hydrolysis and the consequent impact in the aroma production. Lipozyme TL IM® revealed to be an efficient lipase to hydrolyze castor oil (95.4 % of hydrolysis in 48 h). In spite of the higher aroma concentration obtained without lipase, the process was faster when Lipozyme TL IM® was involved, resulting in similar productivities. One of the limitations in the development of an industrial process for γ-decalactone production is the toxicity of the substrate and the lactone. The immobilization by adsorption of Y. lipolytica W29 in methyl polymetacrilate and DupUm® was studied in flasks batch cultures. After selecting the best conditions for cell immobilization, free and immobilized cells were used in the biotransformation of ricinoleic acid into γ-decalactone. The results demonstrated an improvement in γ-decalactone concentration with adsorbed Y. lipolytica cells on DupUM® since a greater amount of γ-decalactone was accumulated in the medium compared to free cells. In this case the use of the extracellular lipase Lipozyme TL IM® in the biotransformation medium was crucial to allow castor oil hydrolysis, without it the substrate access to the cells would be impossible. Furthermore, immobilized cells hold a stable γ- decalactone production after being stored for 30 days at 4 ºC. Also after reuse in three consecutive biotransformations, γ-decalactone concentration was ca. 80 % of that in the first cycle, indicating that immobilized cells could be reused for at least three cycles. The production of γ-decalactone in batch cultures of Y. lipolytica W29 free cells was studied at bioreactor level and the preformance in stirred tank (STR) and airlift bioreactors was compared. The oxygen mass transfer was characterized and the positive influence of kLa on γ-decalactone productivity was demonstrated for both bioreactors. A 2-fold increase in γ-decalactone concentration was achieved in the airlift when compared to STR; but, in this last bioreactor the production rate was higher. Morphological characterization of the yeast cells by image analysis showed that pneumatic agitation causes less impact in the cells morphology than mechanical agitation. A predominance of loose cells and quite irregular structures was observed in the STR. So, the airlift bioreactor presents potential interest for larger scale production, with important cost savings, due to the reduction of power input consumption. Finally, the performance of Y. lipolytica strains with modifications in the lipid metabolism at the β-oxidation pathway (acyl-CoA oxidases) and the triglyceride hydrolysis (LIP2 overexpression) using castor oil as substrate was monitored in the STR bioreactor. Depending on genotype, degradation of γ- decalactone was prevented. Also, a faster initial rate of aroma production was obtained with strain overexpressing LIP2 due to the fast hydrolysis of castor oil and release of ricinoleic acid. Step-wise fedbatch cultures improved γ-decalactone concentration only for MTLY40-2P strain, for which a 1.7-fold increase in γ-decalactone final concentration was achieved. The present work brings new insights on the biotechnological production of γ-decalactone contributing with some different strategies for increasing aroma production leading to a greater γ- decalactone concentration. |
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