Phaffia rhodozyma biorefinery: A sustainable pathway to obtain natural pigments and production of methane biogas as renewable fuel

As the world strives to create a more sustainable and healthier lives, natural pigments are coming to the fore in an attempt to minimize the use of synthetics counterparts and shift the focus towards microbial sources. In this in mind, the yeast Phaffia rhodozyma was used in this study, in a biorefinery context, as biomass feedstock for the intracellular astaxanthin production and reuse of biomass to produce biogas (cf., methane). A sustainable extraction procedure using bio-based solvents was established to directly recover astaxanthin-rich extract from P. rhodozyma dry biomass. The molecular influence of the solutes and solvents involved in the solid–liquid extraction procedures was investigated. Envisioning the full sustainability of the process, and to estimate if the biosolvents used to the process is astaxanthin-friendly, the evaluation of antioxidant activity was confirmed by determining the antioxidant activity using Electron Paramagnetic Resonance (EPR) and toxicological (mutagenicity and ecotoxicity) properties of astaxanthin-rich extract, and the recyclability of solvent was efficiently accomplished. Furthermore, to demonstrate the circularity of the process, the remaining biomass (waste biomass) obtained after astaxanthin-rich extract recovery was effectively used in methanogenic process to produce biogas. The anaerobic digestion used to evaluate methane production from the waste biomass demonstrated the potential to generate 86.88 kWh/year, 225,774.95 kcal/year and 10,287.53 kg/year of electricity, heat recovery and savings on waste management in an P. rhodozyma plant/biorefinery, respectively.