Assessment of the use of a selection of natural deep eutectic solvents in the extraction of polar bioactive compounds from orange peel

Introduction: Polyphenols are abundant plant metabolites with bioactive properties. Conventional extractions are associated with toxic organic solvents. One alternative is the use of Natural Deep Eutectic Solvents (NADES). This work measured Total Polyphenols (TP) and Total Antioxidant Capacity (TAC) of 5 NADES orange peel extracts, comparing its results with a conventional solvent and checking its stability.

Materials and methods: Extraction from orange peel was performed by magnetic stirring. Five NADES (Choline Clorure:Glucose [ChCl:Glu] 2:1, Choline Clorure:Citric Acid [ChCl:CitAc] 2:1, Citric Acid:Glucose [CitAc:Glu] 1:1, Choline Clorure:Glycerol [ChCl:Gly] 3:1 and Glucose:Glycerol [Glu:Gly] 3:1) were selected from a previous bibliographic search (1-4), based on the best TP extraction (5) and TAC results (6) of NADES, and mixed with water (70%) to improve the polarity property. The tests were compared with ethanol-water [EtOH-H₂O] (50%, v:v). The extracts stability, at 4 ºC for 4 weeks, has been verified as well. And, DPPH and Folin-Ciocalteau methods were used, respectively, for TAC and TP determinations.

Results and discussion: The highest TP extraction and TAC were obtained using ChCl:CitAc (5180mg GAE/100g dry matter) and ChCl:Gly (52% DPPH reduction), respectively. EtOH-H₂O extract results (4680mg GAE/100g and 29% DPPH reduction) were lower than most of NADES extracts. In addition, TP retention was similar in all extracts 95-80%. TAC retention was 98-78% except EtOH-H₂O extract (44%). After 15 days, all extracts presented significative differences (p<0.05) with a decrease of TP content and reduction in TAC measurement. Other studies which mixed NADES with 70-80% of water, obtained 5200mg GAE/100g fresh weight in the extraction of TP (1) and 59% DPPH reduction (7). The results were comparable to the present study.

Conclusion:

Tested NADES with high water content provided better extraction efficiency of polar bioactive compounds than the conventional solvent used.

After preparation, 15 days was estimated as useful time for the extracts.

References:

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