Investigation on the effects of cultivation conditions, fed-batch operation, and enzymatic hydrolysate of corn stover on the astaxanthin production by Thraustochytrium striatum

Abstract

Marine protists have recently been studied for the production of high-value bioactive compounds such as polyunsaturated fatty acids and carotenoids. This paper researched astaxanthin production by Thraustochytrium striatum. The studies on carbon and nitrogen sources showed that glucose and yeast extract + peptone (YEP) were the best C and N sources, respectively to achieve maximum cell growth and astaxanthin concentration/content except that ammonia chloride led to the maximum astaxanthin content. The effects of cultivation conditions were comprehensively studied on cell growth and astaxanthin production including glucose/YEP concentrations, salinity, initial medium pH, and temperature. The optimum cultivation conditions favoring cell growth were 40 g/L of glucose, 16 g/L of YEP, 100% artificial seawater of salinity, initial pH 7.0, and 15 °C. The favorable growth conditions were almost consistent with that for astaxanthin concentration, but not for astaxanthin content of cells. Glucose concentration of 40 g/L achieved the highest astaxanthin concentration of 1.5 mg/L, but the maximum astaxanthin content of 0.5 mg/g dry cell mass occurred at 100 g/L of glucose. In addition, 4.0 g/L instead of 16 g/L of YEP led to the maximum astaxanthin concentration and content. Certain oxidative stress including aeration, H2O2 and illumination were found to effectively induce astaxanthin production, but need to be well controlled at certain level. In general, unfavorable growth conditions caused growth stress that stimulated astaxanthin accumulation in cells. Using pure glucose and enzymatic hydrolysate of NaOH pretreated corn stover as a carbon source separately, we found that fed-batch was more effective than batch to achieve both high cell mass and astaxanthin production. With glucose, about double cell mass and triple astaxanthin content were achieved by fed-batch, reaching 9.7 g/L and 6.2 mg/L, respectively. The enzymatic hydrolysate could be low cost carbon source for astaxanthin production by T. striatum.