APPLICATION OF IONIC LIQUIDS FOR CAROTENOIDS EXTRACTION FROM ORANGE PEEL: GREATER YIELD AND THERMAL STABILLITY

Brazil is responsible for 50% of world production of orange juice, implying in large amounts of waste. These by-products can represent interesting sources of many bioactive compounds, as the carotenoids, which are natural pigments with antioxidant properties. These compounds could be used in substitution to artificial pigments by the food industry, and ionic liquids (ILs) can be a viable alternative to the conventional organic solvents (COSs) on carotenoids extraction. So, the aim of this work was to determine a new method of carotenoids extraction from orange peel, using ILs, and evaluate the thermal stability of this extract, since that food industrial processes usually involve heating.
A conventional extraction with acetone was performed to compare the results from the ILs extractions. Four different ILs were tested: 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and 1-hexyl-3-methylimidazolium chloride ([HMIM][Cl]). The Response Surface Methodology was used to select the most efficient IL and to optimize the best conditions of extraction. The determination of carotenoids was performed by HPLC–DAD–MSn, and the thermal stability of the carotenoids extracts (acetone and IL) were evaluated against two different temperatures: 60 °C and 90 °C; and two different mediums: oily and aqueous.
The most efficient IL the [BMIM][Cl] and the best extraction conditions were: the use of ultrasound probe, considering a solid-liquid ratio 1:3, proportion of IL/ethanol 1:2, for 5 minutes and six repetitions. The total carotenoids contents were 7.88±0.59 and 32.08±2.05 µg/g in the extracts obtained with acetone and IL, respectively. The majority carotenoids identified were: 9-cis-violaxanthin and all-trans-lutein in both extracts, along with all-trans-β-carotene in acetone extract, and all-trans-violaxanthin in IL. The 90 ºC heating implied in higher degradations; the HPLC analysis indicated a pronounced degradation of 9-cis-violaxanthin and all-trans-violaxanthin (losses of 98.3% and 100%, respectively) in the acetone extract, and of 100% for both carotenoids in the IL extract. The all-trans-lutein was the most stable xanthophyll (losses of 48.8% in acetone and 3.6% in IL extracts). A comparison of the t1/2 values of both extracts at different temperatures showed that results were independent of the reaction media (oily or aqueous); and the deactivation energy (Ea) for the IL extract was higher under both conditions, confirming that the carotenoids extracted with IL were more stable than those obtained with acetone.
The use of [BMIM][Cl] led to a higher carotenoids yield and a more thermally stable extract compared to the acetone. This method resulted in a green approach of carotenoids extraction, enabling to be employed by the food industry and improving the use of orange sub-products.
Acknowledgments: The authors acknowledge the Brazilian Foundation FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) for financial support (process numbers 2015/26789-5 and 2016/18910-1).