Biotechnological Production of Microalgal Carotenoids with reference to Astaxanthin and Evaluation of its Biological Activity

Sandesh Kamath, B. (2007) Biotechnological Production of Microalgal Carotenoids with reference to Astaxanthin and Evaluation of its Biological Activity. PhD thesis, University of Mysore.

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Abstract

Microalgal biotechnology has gained importance due to its potential to produce bioactive compounds. Green alga Haematococcus pluvialis, being a potent source for ketocarotenoid astaxanthin, has been an attractive species for commercial exploitation. The present work focused on production of astaxanthin from H. pluvialis and evaluation of its biological activity. Modified medium was developed for autotrophic cultivation of H. pluvialis in open and closed system. Haematococcus was grown in different prototype bioreactors under optimized culture condition. The high biomass yield in closed tubular bioreactors suggested that maintenance of the constant carbon dioxide level in the airspace is essential for effective gas-liquid mass transfer. Maximum biomass yield of 0.89 g/L with a growth rate of 0.13 d-1 and astaxanthin content of 1.8% (w/w) was obtained in closed tubular bioreactor. H. pluvialis culture of 60 L prototype raceway tank, after 9 to 12 days growth period and exposed to sunlight and salinity stress for 5 days, produced a biomass yield of 0.5 g/L and astaxanthin content of 1.4 % (w/w). Digital image processing based method was developed for estimation of carotenoid content in H. pluvialis cells, a good correlation of R²=0.967 was observed between carotenoid content as estimated by analytical method. H. pluvialis mutants were isolated using chemical and physical mutagen treatment and were characterized for growth, astaxanthin production, photosynthetic property and carotenoid gene expression. Mutants obtained with 1- methyl 3-nitro 1-nitrosoguanidine (NTG) have shown significant enhancement in total carotenoid and astaxanthin content (23-59% w/w) in comparison with parent culture. The mutant obtained by UV irradiation showed highest lycopene cyclase activity (458 nmole of β-carotene formed/mg of protein/hr) followed by NTG mutant (315 nmole of β-carotene formed/mg of protein/hr) when compared to that of parent strain (105 nmole of β-carotene formed/mg of protein/hr). Expression analysis of carotenoid biosynthetic genes in the mutants exhibited increase in transcript levels compared to wild type. iv Astaxanthin esters and free astaxanthin from H. pluvialis were evaluated for their biological activity. Results indicated that free astaxanthin from H. pluvialis has 4.4 fold higher free radical scavenging activity (IC50 value of 8.1μg/ml) when compared to that of astaxanthin esters. Free astaxanthin also showed maximum reducing power of 59.6U/g equivalents to that of tannic acid (48.5 U/g). The above data showing better antioxidant activity of free astaxanthin is substantiated by comparing with the activity of standard astaxanthin. Free astaxanthin exhibited 5 fold higher soybean lipoxygenase inhibitory activity (IC50 ∼3.4 μg/ml) when compared to total carotenoid fraction. Further, astaxanthin esters effectively inhibited the gastric proton potassium ATPase enzyme that is involved in the acid secretion during gastric conditions. Free astaxanthin was potent inhibitor of gastric H+ K+ ATPase with IC50 -6.2μg/ml than astaxanthin esters (IC50 – 18.2 μg/ml). Results of in vivo studies revealed that astaxanthin esters at 500μg/kg b.w., protected ulcerous condition in rats by ∼67% equivalent to that of known antiulcer drug- omeprazole which offered ∼72% protection at 20 mg/kg b.w. Attractive skin colouration in ornamental fish was achieved by feeding astaxanthin rich H. pluvialis biomass. Poultry birds fed with astaxanthin rich H. pluvialis showed an increase in yolk colour intensity as indicated by Roche Yolk colour fan (Yolk colour score-11.00) and improved egg quality as per FAO standards (Haugh unit score -76 and USDA grade AA). A maximum of 44μg of carotenoid content per gram of yolk was observed in experimental birds, which is 2-3 fold higher compared to control (15μg/g of egg yolk). The findings of this study have substantiated biological activity of astaxanthin such as antioxidant, pigmentation efficiency and established its antiulcer properties. It has also provided insight on autotrophic cultivation of Haematococcus pluvialis for production of astaxanthin.

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Microalgal biotechnology Green alga Haematococcus pluvialis astaxanthin biological activity
Subjects:	600 Technology > 05 Chemical engineering > 01 Biotechnology and Bioengineering 500 Natural Sciences and Mathematics > 07 Life Sciences > 04 Microbiology > 01 Algae
Divisions:	Plant Cell Biotechnology
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	07 May 2009 05:04
Last Modified:	28 Dec 2011 10:07
URI:	http://ir.cftri.res.in/id/eprint/8925

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