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Title: Production of astaxanthin from corn fiber as a value-added co-product of fuel ethanol fermentation

item Nghiem, Nhuan
item Johnston, David

Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2008
Publication Date: 10/29/2008
Citation: Nghiem, N.P., Montanti, J., Johnston, D. 2009. Production of astaxanthin from corn fiber as a value-added co-product of fuel ethanol fermentation. Applied Biochemistry and Biotechnology. 154:227-237.

Interpretive Summary: Fuel ethanol currently is produced by either a dry-grind process or a wet-mill process. In both of these processes, the values added from the co-products are extremely important. Without these co-products, fuel ethanol production is not economically viable. Astaxanthin is one of the potential new co-products of fuel ethanol production. This carotenoid probably is best known for its role in giving the flesh of salmonids, shrimps, lobsters and crayfish the pinkish-red hue. In the marine environment, astaxanthin is acquired through ingestion of microalgae and phytoplankton, which are natural astaxanthin producers. However, since salmonids are unable to synthesize astaxanthin, the farm-raised fish need to be fed this carotenoid through their artificial diets. Astaxanthin is a high-value specialty product. The selling price for astaxanthin in 2000 was estimated at ~$2,500/kg and that of 10% astaxanthin feed formulas in 2007 was listed at $250/kg. The world market for astaxanthin was predicted to reach over $250 million in 2009. Recently astaxanthin was discovered to provide many human health benefits. These discoveries could lead to development of nutraceutical applications and significant expansion of the market for astaxanthin. Currently astaxanthin is produced commercially by either chemical synthesis or microbial fermentation. The market has been heavily dominated by the synthetic product mainly due to its much lower production cost. However, growing demand for products from natural sources may open up the market to astaxanthin produced by biological processes. There are only two microbial astaxanthin sources that may be able to compete economically with synthetic astaxanthin. These are the green microalga Haematococcus pluvialis and the red yeast Phaffia rhodozyma. The yeast P. rhodozyma is of particular interest since several strains can utilize various sugars, including glucose, xylose and arabinose, for growth and astaxanthin synthesis. Thus, P. rhodozyma can be used for astaxanthin production using fermentable sugars obtained from hydrolysis of lignocellulosic biomass as carbon sources. The objective of our research program is to develop a process for production of astaxanthin as a high value-added co-product of corn-based fuel ethanol. We report here the screening of several strains of P. rhodozyma for their capability of utilizing fermentable sugars obtained from corn fiber (a ligno cellulosic byproduct from fuel ethanol production from corn) for astaxanthin production. From the data obtained production of astaxathin by fermentation of ethanol byproducts appears promising.

Technical Abstract: Five strains of the yeast Phaffia rhodozyma, NRRL Y-17268, NRRL Y-17270, ATCC 96594 (CBS 6938), ATCC 24202 (UCD 67-210), and ATCC 74219 (UBV-AX2) were tested for astaxanthin production using the major sugars derived from corn fiber, a byproduct from the wet milling of corn kernels that contains primarily cellulose and hemicellulosic polysaccharides. The sugars tested included glucose, xylose and arabinose. All five strains were able to utilize the three sugars for astaxanthin production. Among them ATCC 74219 was the best astaxanthin producer. Kinetics of sugar utilization of this strain was studied, both with the individual sugars and with their mixtures. Arabinose was found to give the highest astaxanthin yield. It also was observed that glucose at high concentrations suppressed utilization of the other two sugars. Corn fiber hydrolysate obtained by dilute sulfuric acid pretreatment and subsequent enzyme hydrolysis was tested for astaxanthin production by strain ATCC 74219. Dilution of the hydrolysate was necessary to relieve the inhibition of the compounds formed during the acid pretreatment. All the sugars in the hydrolysate diluted with two volumes of water were completely consumed. Astaxanthin yield of 0.82 mg/g sugars consumed was observed.