Studies on the growth of the carotenoid-producing yeast Phaffia rhodozyma in caprine casein hydrolysate
Abstract: The food yeast Phaffia rhodozyma synthesizes astaxanthin, which is the orange-pink carotenoid that imparts color to salmonids such as trout and salmon. The commercial value of these fish is influenced by the color of their flesh, and in aquaculture operations astaxanthin has to be incorporated into their feed. Because synthetic astaxanthin and canthaxanthin pigments are expensive additives in the diet of cultivated fish, research has been conducted to develop a fermentation process for P. rhodozyma with high mass productivity and yield, as the first step to obtain an economical production of a natural source for astaxanthin. Preliminary studies using caprine casein hydrolysate as a substrate for Saccharomyces cerevisiae, a yeast instrumental to winemaking, baking, and brewing, have shown that it has enhancing effects on the growth of such a commercially important yeast. The objective of this work was to study the effects of caprine casein hydrolysate as substrate for P. rhodozyma on the yeast growth and astaxanthin production. Flask fermentation experiments with P. rhodozyma were conducted to find the optimum values for the parameters temperature, pH, and fermentation time. The dry biomass concentration and astaxanthin concentration of P. rhodozyma grown in caprine casein hydrolysate under optimized conditions of 21oC and a pH of 6, for 76 h, were 10.3± 0.4 g/L and 14.2 mg/L ± 0.01, respectively. Those values were statistically significant higher than those found using bovine casein hydrolysate. The finding that caprine casein hydrolysate enhances the biomass growth and astaxanthin concentration will contribute to the design of a low-cost culture media for the commercial production of this carotenoid-producing yeast.
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