Publicação
Production of the sweetener erythritol by Yarrowia lipolytica strains
| Resumo: | Nowadays, the demand for alternatives to sugar has become a priority. Erythritol is a sugar alcohol with nearly 70 % of sucrose sweetness, with zero calories, non-cariogenic and non-glycemic. This sweetener is produced through fermentation from glucose mostly by osmophilic microorganisms. The osmotolerant yeast Yarrowia lipolytica can produce erythritol from crude glycerol, a by-product of biodiesel industry. The production of erythritol by this yeast can be affected by several parameters, such as yeast strain, medium composition and operating condition. The main objective of the present work was the development of a process for erythritol production by Y. lipolytica using crude glycerol as carbon source. Initially, a screening for osmotolerant strains of Y. lipolytica was performed using two different methodologies: assessment of cell growth in agar plates containing 1 M of NaCl and miniaturized assays in liquid medium supplemented with NaCl. Nine strains that grew better in the medium with salt were selected and their capability to produce erythritol was tested. The strains W29, UV15-31, UV15-93 and EMS75-162 produced the higher concentrations of erythritol. The scale-up of the process in a stirred tank reactor was performed only with the strain Y. lipolytica W29. The effect of dissolved oxygen in the production of erythritol was assessed, using two different strategies: constant aeration and stirring rates and controlled dissolved oxygen concentration. The results showed that dissolved oxygen concentration in the medium is an important parameter that influences the erythritol productivity. The highest concentration of erythritol (32 g·L-1), yield (0.43 g·g-1) and productivity (0.44 g·L-1·h-1) were obtained in the batch performed at high constant stirring and aeration rates, 900 rpm and 3 vvm, respectively. Some strategies of fed-batch operation were also performed to evaluate if the erythritol production could be extended with glycerol feeding to Y. lipolytica culture. The different strategies tested were fed-batch at constant feeding rates with completed and concentrated medium, fed-batch at constant feeding rate only with addition of crude glycerol, and a step-wise fed-batch with the addition of crude glycerol. It was observed that erythritol accumulation in the medium was extended with the addition of only crude glycerol to the bioreactor. The step-wise fed-batch proved to be the best strategy among the tested ones, leading to highest yield (0.42 g·g-1) and productivity (0.45 g·L-1·h-1). |
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| Autores principais: | Machado, Ana Rita Araújo |
| Assunto: | Erythritol Yarrowia lipolytica Crude glycerol Eritritol Yarrowia lipolytica Glicerol bruto |
| Ano: | 2018 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Nowadays, the demand for alternatives to sugar has become a priority. Erythritol is a sugar alcohol with nearly 70 % of sucrose sweetness, with zero calories, non-cariogenic and non-glycemic. This sweetener is produced through fermentation from glucose mostly by osmophilic microorganisms. The osmotolerant yeast Yarrowia lipolytica can produce erythritol from crude glycerol, a by-product of biodiesel industry. The production of erythritol by this yeast can be affected by several parameters, such as yeast strain, medium composition and operating condition. The main objective of the present work was the development of a process for erythritol production by Y. lipolytica using crude glycerol as carbon source. Initially, a screening for osmotolerant strains of Y. lipolytica was performed using two different methodologies: assessment of cell growth in agar plates containing 1 M of NaCl and miniaturized assays in liquid medium supplemented with NaCl. Nine strains that grew better in the medium with salt were selected and their capability to produce erythritol was tested. The strains W29, UV15-31, UV15-93 and EMS75-162 produced the higher concentrations of erythritol. The scale-up of the process in a stirred tank reactor was performed only with the strain Y. lipolytica W29. The effect of dissolved oxygen in the production of erythritol was assessed, using two different strategies: constant aeration and stirring rates and controlled dissolved oxygen concentration. The results showed that dissolved oxygen concentration in the medium is an important parameter that influences the erythritol productivity. The highest concentration of erythritol (32 g·L-1), yield (0.43 g·g-1) and productivity (0.44 g·L-1·h-1) were obtained in the batch performed at high constant stirring and aeration rates, 900 rpm and 3 vvm, respectively. Some strategies of fed-batch operation were also performed to evaluate if the erythritol production could be extended with glycerol feeding to Y. lipolytica culture. The different strategies tested were fed-batch at constant feeding rates with completed and concentrated medium, fed-batch at constant feeding rate only with addition of crude glycerol, and a step-wise fed-batch with the addition of crude glycerol. It was observed that erythritol accumulation in the medium was extended with the addition of only crude glycerol to the bioreactor. The step-wise fed-batch proved to be the best strategy among the tested ones, leading to highest yield (0.42 g·g-1) and productivity (0.45 g·L-1·h-1). |
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