A method for increasing the content of ubiquinone (CoQ10) and ubiquinol (CoQH2) in phototrophic microorganisms that were cultivated in a culture medium in a bioreactor under light irradiation, wherein the phototrophic microorganisms are selected from the group consisting of blue algae, green algae and yellow-green algae, comprising a step of inducing oxidative stress. By virtue of the fact that oxidative stress was induced by incubating the phototrophic microorganisms together with Fe3+ in the culture medium, a higher content of CoQ10 and CoQH2 is obtained. Moreover, the microorganisms thus obtained have a higher content of trivalent iron, which is particularly relevant for the human diet. From the phototrophic microorganisms it is possible to produce an oily extract and also a dried algae product.
