β-Carotene production enhancement by UV-A radiation in Dunaliella bardawil cultivated in laboratory reactors

Abstract β-carotene is an antioxidant molecule of commercial value that can be naturally produced by certain microalgae that mostly belong to the genus Dunaliella . So far, nitrogen starvation has been the most efficient condition for enhancing β-carotene accumulation in Dunaliella . However, while nitrogen starvation promotes β-carotene accumulation, the cells become non-viable; consequently under such conditions, continuous β-carotene production is limited to less than 1 week. In this study, the use of UV-A radiation as a tool to enhance long-term β-carotene production in Dunaliella bardawil cultures was investigated. The effect of UV-A radiation (320–400 nm) added to photosynthetically active radiation (PAR, 400–700 nm) on growth and carotenoid accumulation of D. bardawil in a laboratory air-fluidized bed photobioreactor was studied. The results were compared with those from D. bardawil control cultures incubated with PAR only. The addition of 8.7 W·m − 2 UV-A radiation to 250 Wm − 2 PAR stimulated long-term growth of D. bardawil . Throughout the exponential growth period the UV-A irradiated cultures showed enhanced carotenoid accumulation, mostly as β-carotene. After 24 days, the concentration of β-carotene in UV-A irradiated cultures was approximately two times that of control cultures. Analysis revealed that UV-A clearly induced major accumulation of all-trans β-carotene. In N-starved culture media, β-carotene biosynthesis in UV-A irradiated cultures was stimulated. We conclude that the addition of UV-A to PAR enhances carotenoid production processes, specifically all-trans β-carotene, in D. bardawil cells without negative effects on cell growth.