Natural Deep Eutectic Solvents As Main Solvent For The Extraction Of Total Polyphenols Of Orange Peel

Every year food industry produces a great amount of waste, mainly in citric industry, where 18% of the citric fields are made for industrial processes¹. Conventionally organic solvents, such as methanol or dichloromethane, have been used for the extraction of bioactive compounds from plants and vegetables. Lately an alternative to organic solvents, Natural Deep Eutectic Solvents (NADES), have increased².

Four combinations of NADES were made. The mixtures were determinated by their molar mass, where choline chloride (ChChl), betaine (Bet) and L-proline (L-P) acted as hydrogen bond acceptor and fructose (Fruc), malic acid (MA), citric acid (CA) and glycerol (Gly) acted as hydrogen bond donor. The NADES were mixed with different amount of water (10 up to 85%).

Total polyphenols (TP) were determined in orange peel. Firstly, it was crushed to obtain the highest extraction. Different concentration (ratio solid/liquid) and extraction time were defined, and it was carried out by magnetic stirring and heating to 45±5ºC. The amount of TP was measured in fresh orange peel, then the values were calculated in dry sample.

Results show that at concentrations of 1g/5ml using ChChl:Fruc, ChCHl:Gly and Bet:CA the largest amount of TP was extracted. Indeed, ChChl:Fruc extracted 6530 mgGAE/100g at 50% in water and for 30 minutes. The sample extracted with ChChl:Gly had its greatest extraction at 10% in water and during 19 minutes of extraction (1657 mgGAE/100g). In the case of samples extracted with Bet:CA, the best conditions were obtained during 30 minutes and 12% of NADES in water (10257 mgGAE/100g). The L-P:MA mixture at 50% in water, ratio 1g/17ml and 30 minutes extracted the largest amount of TP (4294 mgGAE/100g). The extraction of TP using organic solvents (methanol) gave lower results (955 mgGAE/100g)³, being able to conclude that NADES could be an eco-friendly alternative to extract TP from orange peel.

Acknowledgement: This work was funded by the Spanish Ministry of Science and Innovation - State Bureau of Investigation (PID2019-111331RB-I00/AEI/10.13039/501100011033)

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