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. 2023 Jan 11:13:1072592.
doi: 10.3389/fpls.2022.1072592. eCollection 2022.

Natural deep eutectic solvents as a green extraction of polyphenols from spent coffee ground with enhanced bioactivities

Aitor García-Roldán  1 , Léa Piriou  2 , Paula Jauregi  1   3
Affiliations

Natural deep eutectic solvents as a green extraction of polyphenols from spent coffee ground with enhanced bioactivities

Aitor García-Roldán et al. Front Plant Sci. .

Abstract

Conventional extraction techniques are usually based on highly pollutant and/or flammable organic solvents. Therefore, alternative environmentally friendly extraction methods are of particular interest for the recovery of bioactive compounds for their application as food ingredients and/or nutraceuticals. Natural deep eutectic solvents (NADES) are a green and nontoxic attractive alternative to hydroalcoholic extraction. NADES media primarily depends on the intermolecular interactions (hydrogen bonding) among their components to form a eutectic mixture with a much lower final melting point than its individual components. Examples of natural deep eutectic NADES solvents include aqueous solutions (25%-50% water) of choline chloride, sugars, and polyols. This study aimed to investigate the application of two NADES, namely, betaine:triethylene glycol (Bet : TEG) and choline chloride:1,2-propanediol (Chol : Prop), as sustainable green solvents for the extraction of polyphenols from spent coffee ground (SCG), a by-product of coffee processing. In particular, the extraction yield and selectivity were evaluated and compared with conventional green extractions (hot water and a hydroalcoholic solution). In addition, the effect of NADES on the antioxidant and antimicrobial activity of the extracts was investigated. The main outcomes were as follows: (i) NADES were as effective as other conventional green solvents in the extraction of polyphenols with the added advantage of operating at milder temperature conditions, without flammable solvents and with sustainable and natural compounds; (ii) the antimicrobial activity of the NADES extracts was 10 times higher than that of the ethanolic and aqueous extracts. Given the low toxicity of NADES, they could be used as formulation aid for food ingredients.

Keywords: antimicrobial activity; antioxidant activity; extraction; natural deep eutectic solvent (NADES); polyphenols; selectivity; spent coffee ground.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Viscosity evolution of both NADES with different dilution factors.
Figure 2
Figure 2
Total phenolics (TP) content expressed in gallic acid equivalents (GAE) % of dry weight (DW) and antioxidant activity expressed in Trolox equivalent (TE) µmol/g DW. Letters above error bars stand for statistically significant differences between groups.
Figure 3
Figure 3
(A) Protein and reducing sugars content expressed in % of dry weight (DW). (B) Caffeine content expressed in % of dry weight (DW). Letters above error bars stand for statistically significant differences between groups.
Figure 4
Figure 4
Pie charts representing the composition of phenolics, protein, and reducing sugars for each extract.
Figure 5
Figure 5
Inhibitory activity (%) of the extracts at the highest dilution and the corresponding solvents alone at the same dilution for Chol : Prop 60% and Bet : TEG 60%; the total polyphenol concentration (GAE mg/ml) in each extract was as follows: 830 (aqueous), 838 (ethanolic), 153 (Chol : Prop 50%), 141 (Chol : Prop 60%), 101 (Bet : TEG 70%), and 148 (Bet : TEG 60%).
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