β-Carotene production and extraction: a case study of olive mill wastewater bioremediation by Rhodotorula glutinis with simultaneous carotenoid production

Over the last few years, there has been an impetuous search for natural colorant to be applied in various industries, such as cosmetics, food, and textile. This is largely driven by an increasing consumer demand for formulated ingredient products that are not only considered safer than their synthetic counterparts, but also present medicinal health benefits. However, there are a limited number of commercially available soluble organic pigments. Rhodotorula glutinis yeast can be used for the biodegradation of phenols rich olive mill wastewater, which is an abundant and jeopardous polluting waste, while simultaneously producing multiple high-added value compounds, such as the natural colorant beta-carotene. Herein, the protocols were firstly optimized by screening 10 different solvents while evaluating their aptitude to dissolve pure beta-carotene. The results followed the trend: water approximate to methanol < ethanol < acetonitrile < acetone < dichloromethane < diethyl ether < heptane < ethyl acetate < benzene. However, due to the high toxicity of benzene and the carotenoid precipitation by heptane, ethyl acetate, diethyl ether, and dichloromethane were selected as the most promising solvents. Thus, an integrated process for the extraction, isolation, and concentration of beta-carotene was proposed from Rhodotorula glutinis, cultivated in (processing) effluent. The extraction results followed the same tendency as for pure carotenoid: dichloromethane (13 +/- 1 mu g g(-1) yeast) < diethyl ether (15 +/- 2 mu g g(-1) yeast) < ethyl acetate (21 +/- 2 mu g g(-1) yeast). Regarding liquid-liquid extraction, the maximum extraction efficiency was also achieved with ethyl acetate, i.e., 100 +/- 28%. Overall, these results show promising findings for a cascade biorefinery downstream process, as this not only potentially reduces the burden on the environment, but also adds value to primary economic activity.