Statistical optimization for tannase production by Aspergillus tubingensis in solid-state fermentation using tea stalks

Background A sequential statistical strategy was used to optimize tannase production from Aspergillus tubingensis using tea stalks by solid-state fermentation. Results First, using a Plackett-Burman design, inoculum size and incubation time (among seven tested variables) were identified as the most significant factors for tannase yield. The effects of significant variables were further evaluated through a single steepest ascent experiment and central composite design with response surface analysis. Under optimal conditions, the experimental value of 84.24 units per gram of dry substrate (U/gds) closely matched the predicted value of 87.26 U/gds. Conclusions The result of the statistical approach was 2.09 times higher than the basal medium (40.22 U/gds). The results were fitted onto a second-order polynomial model with a correlation coefficient (R²) of 0.9340, which implied an adequate credibility of the model.

Study on the relationship between intracellular metabolites and astaxanthin accumulation during Phaffia rhodozyma fermentation

Background To study the relationship between intracellular anabolism and astaxanthin production, the influence of intracellular protein and fatty acids on astaxanthin production by four mutant Phaffia rhodozyma strains and their variations was investigated in this research. Results First, the content of astaxanthin in cells showed a reverse fluctuation in contrast to that of protein during the whole fermentation process. Moreover, compared with the three other strains, the astaxanthin-overproducing mutant strain of the yeast P. rhodozyma, called JMU-MVP14, had the highest specific productivity of astaxanthin as 6.8 mg/g, whereas its intracellular protein and fatty acid contents were the lowest. In addition, as a kind of sugar metabolic product, ethanol was only produced by P. rhodozyma JMU-VDL668 and JMU-7B12 during fermentation. Conclusions The results indicated that the accumulation of ethanol, intracellular protein, and fatty acids had competition effects on astaxanthin synthesis. This condition may explain why the P. rhodozyma strains JMU-VDL668 and JMU-7B12 achieved relatively lower astaxanthin production (1.7 and 1.2 mg/L) than the other two strains JMU-MVP14 and JMU-17W (20.4 and 3.9 mg/L).