Abstract
Different cultivation strategies have been developed with the aim of increasing the production rate of microalgal pigments. Specifically, biotechnological approaches are designed to increase antioxidant metabolites as chlorophyll and carotenoids. However, although significant advances have been built up, available information regarding both the chlorophyll metabolism and their oxidative reactions in photobioreactors is scarce. To unravel such processes, the detailed chlorophyll and carotenoid fraction of Scenedesmus obliquus has been studied by HPLC-ESI/APCI-hrTOF-MS from phototrophic and heterotrophic cultures. Scenedesmus is provided with a controlled strategy of interconversion between chlorophyll a and b to avoid the formation of reactive oxygen species (ROS) at high irradiances in addition to the photoacclimation of carotenoids. Indeed, precise kinetics of 132-hydroxy- and 151-hydroxy-lactone chlorophyll metabolites shows the existence of a chlorophyll oxidative metabolism as a tool to manage the excess of energy at high light conditions. Unexpectedly, the oxidation under phototrophy favored chlorophyll b metabolites over the chlorophyll a series, while the heterotrophic conditions exclusively induced the formation of 132-hydroxy-chlorophyll a. In parallel, during the first 48 h of growth in the dark, the chlorophyll fraction maintained a promising steady state. Although future studies are required to resolve the biochemical reactions implied in the chlorophyll oxidative metabolism, the present results agree with phytoplankton metabolism.
Highlights
Chlorophyll and carotenoids are challenging compounds in microbial biotechnology that find several applications in the food industry
The greatest impact of the type of cultivation was on the biomass productivity, where the highest value was obtained under heterotrophy (19.75 mg/L h), which is a consequence of the low residence time (120 h) reached in this condition, when compared with the phototrophic culture (216 h) that resulted in a productivity of 10.87 mg/L h
Regardless, at very long incubation times during the phototrophic growth, it is impossible to ensure that no nutrient deprivation occurs
Summary
Chlorophyll and carotenoids are challenging compounds in microbial biotechnology that find several applications in the food industry. The present food market trend is towards more natural ingredients, and colorants are not an exception [1]. Artificial food colorants have been associated with health problems and new sources of natural colorants are under investigation. Natural food colorants have been traditionally extracted from fruits and vegetables sources, microalgae are currently a promising natural resource. Several advantages as the fast growth, the high pigment concentration, and the physiologically plasticity, make microalgae the new objective of biotechnological companies for pigment production. Scenedesmus obliquus stands out as source of pigments in food and cosmetics as well as is considered for human consumption [2,3]
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