Ulva spp. carotenoids: Responses to environmental conditions

Despite the green macroalga Ulva spp. be indicated for diverse commercial purposes and cultivated in integrated aquaculture to remediate animal effluents, most of their biomass is not commercially used. As a new application, it could be used as raw material for carotenoids production. To evaluate this, a literature research was conducted on Ulva spp. carotenoids content, their physiological responses to environmental factors and the experimental processing and analysis used. Ulva spp. carotenoids were identified by analysis of absorption spectra and retention times after chromatography separation; these were lutein, beta-carotene, neoxanthin, beta-cryptoxanthin, violaxanthin, antheraxanthin and zeaxanthin. Total carotenoids yield depends on the strain and is positively related to biomass growth. The optimization of the cultivation conditions such as light intensity, nutrients concentration, temperature and salinity can improve carotenoids production. In addition, strategies such as selenium or plant hormones addition, exclusion of incident ultraviolet (UV) light (for few days), and brief induction of physiological stress by extreme hyposalinity, temperature variation and CO2 depletion can further increase this yield. The increase of carotenoids after physiological stress induction would constitute a direct response to maintain the photosynthesis rate and/or eliminate reactive oxygen species (ROS), or indirect, caused by the increase of antioxidant enzymes and other antioxidant metabolites, which would protect them. In this sense, nutrient enrichment is required to cope with oxidative stress. High PAR intensity decrease photosynthetic pigments yield in minutes (and recover after dark period) while photoprotective carotenoids yield remains constant. The activation of the xanthophyll cycle (violaxanthin to zeaxanthin conversion) is dependent on temperature, and can be induced by high light intensity, hypersalinity or desiccation (under dim light). The xanthophyll cycle is the main non-photochemical quenching (NPQ) mechanism in Ulva spp. during the first period of acclimation to high light intensity.