Optimization Of Photobioreactor For Astaxanthin Production In Chlorella Zofingiensis.

Abstract

Microalgae have been known to produce commercially valuable carotenoids beneficial to human health. One of the algal carotenoids that have received a lot of research attention is astaxanthin. Also known as ?king of antioxidant?, astaxanthin is 100 times more than the antioxidant capacity of that of vitamin E, and 10 times more than that of beta-carotene. Chlorella Zofingiensis, a strain of green microalgae, has been shown in recent years to be able to accumulate astaxanthin when exposed to environmental stress. This study investigated the astaxanthin production capacity of Chlorella Zofingiensis under nitrate, light and temperature stress under a semi-continuous turbidostatic flat-bed photobioreactor. A total of 15 configurations consisting of different nitrate concentration and light intensities were tested in a batch system in phase 1 of the experiment. Growth rates and astaxanthin contents were monitored. Highest dry mass of 7.55 g/L was obtained at 0.5 g/L of nitrate and at light intensity of 300 umol photon.m-2s-1. It was found that low nitrate level, coupled with high light intensity, was the key to high cellular accumulation in C. Zofingiensis. Peak volumetric astaxanthin production was at 7.06 mg/L. Using the optimum nitrate/light intensity pair, it was further tested in a flat-bed photobioreactor in semi-continuous mode. Cellular astaxanthin level was at 0.69 mg/g, almost 50% lower than the batch system, but the growth of C. Zofingiensis biomass was more. Volumetric astaxanthin production of semi-continuous system was comparable to batch system. Daily astaxanthin production for continuous system was 21% higher than that of the batch system. Overall, the reported data suggests that C. Zofingiensis is an attractive candidate for the mass production of astaxanthin in continuous reactor, being plausible for selectively favoring the production of astaxanthin through the adequate management of growth conditions.