Antioxidant Capacity of Carotenoid Extracts from the Haloarchaeon Halorhabdus utahensis

Herein, we report on the production, characterization, and antioxidant power assessment ofcarotenoids from the haloarchaeon Halorhabdus utahensis. It was grown at 37 °C and 180 rpm agitationin halobacteria medium supplemented with glucose, fructose, and xylose, each at concentrations of0.2%, 1%, and 2%, and the carotenoid yield and composition were investigated. The microorganismproduced the carotenoids under all the conditions tested, and their amount followed the orderglucose < xylose < fructose. The highest yield was achieved in 2% fructose growth medium with550.60 ug/g dry cell and 2428.15 ug/L. Separation and identification of the carotenoidswere performed by RP-HPLC and HPLC/APCI-ITMSn. Bacterioruberin was the main carotenoid detectedand accounted for 60.6%, 56.4%, and 58.9% in 2% glucose, 1% xylose, and 2% fructose extracts,respectively. Several geometric isomers of bacterioruberin were distinguished, and representatives ofmonoanhydrobacterioruberin, and bisanhydrobacterioruberin were also detected. The assignmentto cis-isomers was attempted through analysis of the UV/Vis spectra, intensity of cis peaks, andspectral fine structures. The extracts exhibited superoxide scavenging activity higher than butylhydroxytoluene,ascorbic acid, and Trolox, selected as antioxidant references. The anti-hyaluronidasecapacity was investigated, and the 2% fructose extract showed the highest activity reaching 90%enzyme inhibition with 1.5 ug. The overall data confirm that Hrd. utahensis can be regarded as aninteresting source of antioxidants that can find applications in the food and cosmetic sectors.