UVB exposure stimulates production of vitamin D3 in selected microalgae

There has been a rise in awareness about the low dietary intake of vitamin D worldwide. Besides being provided through the diet, vitamin D3 can be synthesized in skin when exposed to UVB light. UVB light triggers the conversion of naturally present 7-dehydrocholesterol (provitamin D3) to vitamin D3 in skin. In this study four microalgal species, Tetraselmis suecica, Dunaliella salina, Nannochloropsis oceanica and Nannochloropsis limnetica were cultivated and exposed to UVB (15 kJ/m2/day for 3 days) in order to investigate their ability to produce vitamin D3 by conversion of 7-dehydrocholesterol. In addition, N. oceanica was exposed to UVB as a wet paste and dried biomass in order to investigate vitamin D3 production at different processing steps. Other fat-soluble vitamins and provitamin D3, lipids, fatty acids, proteins and amino acids were determined to evaluate the effect of UVB exposure in N. oceanica and D. salina. Most of the cultures were capable of producing vitamin D3 when UVB exposed (D. salina (145 ± 11 ng/g DM), N. oceanica (285 ± 5 ng/g DM), and N. limnetica (2700 ± 198 ng/g DM)), whereas T. suecica was not able to produce vitamin D3. UVB exposed wet paste and dry biomass of N. oceanica was shown to contain lower levels of 7-dehydrocholesterol and vitamin D3, 13 ± 0.4 ng/g DM and 2 ± 0.2 ng/g DM, respectively, which suggest that the production of 7-dehydrocholesterol is increasing during UVB exposure of the growing diluted cultures. UVB stimulated accumulation of α-tocopherol and β-carotene in D. salina and α-tocopherol in N. oceanica. On the contrary, UVB had an adverse effect on the protein content in D. salina and β-carotene content in N. oceanica. These findings suggest that UVB exposed microalgae has a potential as a new, vegan, natural and sustainable source of vitamin D3.