During fermenter cultivation of Phaffia rhodozyma on a grape juice medium, the presence of glucose initially delayed fructose utilization, although fructose was consumed before glucose depletion. Total pigment and astaxanthin production were growth associated and reached maximum values of 15.9 μg/ml and 9.8 μg/ml, respectively, after depletion of the carbon source. The total cellular pigment and astaxanthin content increased during the stationary growth phase due to a decrease in biomass, reaching final values of 2120 μg/g and 1350 μg/g, respectively, without the volumetric concentration in the culture changing. The final cell yield was 0.33 g/g sugar utilized. High sugar concentrations in shake-flasks as well as O2 limitation decreased the astaxanthin content of the cells. Addition of yeast extract to a grape juice minimal medium markedly increased the maximum specific growth rate, total pigment and astaxanthin content of the cells. An excess of ammonia decreased the intracellular astaxanthin content, which reached a maximal value in cultures with no residual glucose or ammonia.
Mutagenesis of Phaffia rhodozyma with NTG yielded a mutant with an astaxanthin content of 1688 μg (g dry biomass)(-1), a cell yield coefficient of 0.47 on glucose and a maximum specific growth rate of 0.12 h(-1). Re-mutation of the mutant decreased the cell yield and maximum specific growth rate but increased the astaxanthin content. The use of mannitol or succinate as carbon sources enhanced pigmentation, yielding astaxanthin contents of 1973 μg g(-1) and 1926 μg g(-1), respectively. The use of valine as sole nitrogen source also increased astaxanthin production, but severely decreased the maximum specific growth rate and cell yield coefficient. The optimum pH for growth of P. rhodozyma was between pH 4.5 and 5.5, whereas the astaxanthin content remained constant above pH 3.
A Candida blankii yeast isolate was grown in sugar cane bagasse hemicellulose hydrolysate at 38 degrees C in carbon-limited chemostat culture. The pretreatment of the acid hydrolysate prior to microbial cultivation consisted of partial neutralization with ammonia and sodium hydroxide, plus the addition of phosphorus, which was the only other growth-limiting nutrient apart from nitrogen. The cell yield coefficient on nitrogen was 16.78. The critical dilution rate was higher (0.35 h(-1)) in diluted hydrolysate than in undiluted hydrolysate (0.21 h(-1)). In undiluted hydrolysate at a dilution rate of 0.1 h(-1) and pH 4, where aseptic procedures proved unnecessary, the cell and protein yield coefficients were 0.53 and 0.26, respectively, and no residual carbon substrates (D-xylose, L-arabinose, D-glucose, and acetic acid) were detected. The cell yield on oxygen increased linearly as a function of dilution rate. The cellular content of protein, carbohydrate, and RNA also increased with an increase in dilution rate, whereas the DNA content decreased slightly. C. blankii has considerable potential for the production of single cell protein from hemicellulose hydrolysate, because of its ability to utilize all of the major carbon substrates in the hydrolysate at a low pH and at a relatively high temperature with a high protein yield.
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