Astaxanthin production by Phaffia rhodozyma

Abstract

This project concentrated on the use of the commercially available Phaffia rhodozyma NCYC 874 as an astaxanthin source. The purpose of this research was to investigate the optimum conditions for a batch fermentation of the yeast. Cell growth and astaxanthin production by the yeast using two different media was investigated, as previous work has highlighted major differences in the growth and efficiency of astaxanthin production in various media. This research was also concerned with the effect of carbon concentration on pigment levels. Consumption of the nitrogen source by the yeast was also investigated with regard to biomass and pigment production. The parent strain (NCYC 874) of Phaffia rhodozyma and a mutant strain of the yeast (NRRL-Y-18734), were both cultivated in a laboratory scale 2 litre fermenter to compare biomass and astaxanthin yields and the utilisation of the carbon and nitrogen sources. Three different approaches were used to extract astaxanthin from the yeast cells, mechanical breakage, acid lysis and enzyme treatment. Phaffia rhodozyma NCYC 874 produced a higher yield of astaxanthin in the Mineral Salts medium than in the Yeast Malt Broth, which is the commercial medium used for culturing the yeast. Higher astaxanthin yields were obtained using a 1% carbon source. The addition of fresh glucose to the growth medium after five days at the two concentrations used resulted in an increase in astaxanthin yields and cell numbers. Production of biomass by the parent strain of the yeast was found to be more closely linked to the consumption of nitrogen, than to consumption of the carbon source. The opposite was observed to be the case regarding the mutant strain of the yeast, with biomass production found to be more closely linked to consumption of the carbon source. Astaxanthin production by the mutant strain of the yeast was found to be more closely linked to nitrogen consumption. This indicated that the mutant strain was more efficient than the parent strain at utilising the nitrogen source to produce pigment. The opposite was observed to be the case regarding the parent strain, with pigment production found to be more closely linked to consumption of the carbon source. The mutant strain of the yeast produced higher yields of biomass and astaxanthin than the parent strain, when grown in both shake flask and fermenter culture. Consumption of the carbon and nitrogen sources by both strains of the yeast followed the same pattern irrespective of the method of culture used.