Deep Eutectic Solvents as a Green Tool for the Extraction of Bioactive Phenolic Compounds from Avocado Peels

Abstract

Avocado peels are the main agro-industrial residue generated during the avocado processing, being a rich source of bioactive compounds like phenolic compounds. The growing demand for more sustainable processes requires the development of new and effective methods for extracting bioactive compounds from industrial waste. Deep eutectic solvents (DESs) are a new sustainable alternative to toxic organic solvents due to their non-toxicity and biocompatibility. In this study, five selected DESs were applied for the extraction of bioactive phenolic compounds from avocado peels. The extraction efficiency was evaluated by measuring the total phenolics and flavonoids content. The best extraction results were obtained with choline chloride-acetic acid and -lactic acid (92.03 ± 2.11 mg GAE/g DAP in TPC and 186.01 ± 3.27 mg RE/g DAP); however, all tested DESs show better extraction efficiency than ethanol. All the obtained NADES extracts have high antioxidant activity (FRAP: 72.5–121.1 mg TE/g; TAC: 90.0–126.1 mg AAE/g). The synthesized DESs and avocado peels DES extracts had activity against all tested bacteria (Staphylococcus aureus, Streptococcus dysgalactiae, Escherichia coli and Pseudomonas putida), and the extracts prepared with choline chloride-acetic acid and -lactic acid have the highest antibacterial activity against all microorganisms. These results, coupled with the non-toxic, biodegradable, low-cost, and environmentally friendly characteristics of DESs, provide strong evidence that DESs represent an effective alternative to organic solvents for the recovery of phenolic bioactive compounds from agro-industrial wastes.

Valorization of Avocado Seed Wastes for Antioxidant Phenolics and Carbohydrates Recovery Using Deep Eutectic Solvents (DES)

“…Similar behavior was observed by other authors, obtaining higher TPC value when using DES than when using methanol, ethanol or water [ 45 , 48 ]. In the same context, Rodríguez-Martínez et al [ 19 ] reported significant differences ( p < 0.05) for the TPC and TFC values obtained for avocado peel extracted with choline chloride:glycerol (1:3 with 30% of water in its formulation) or with ethanol (96%), reaching 3.1 and 1.6-fold higher values when using the choline chloride:glycerol DES for TPC and TFC, respectively [ 19 ]. For that reason, that DES was selected as the solvent for the following experimental design.…”

“…This value was in the range of avocado seed after extrusion with a value of 15.4 mg/g [ 52 ]. Conversely, higher values of FRAP were obtained from avocado peel extracted with choline chloride:glycerol (1:3) with 30% water content, reaching a value of 84.5 mg TE/g avocado peel after being processed for 120 min at 50 °C [ 19 ].…”

“…One way to recover bioactive molecules from fruit by-products is by using deep eutectic solvents (DES) [ 18 , 19 ]. DES are conformed by a blend of a hydrogen-bond acceptor (HBA) and a hydrogen-bond donor (HBD) in a suitable molar ratio that allows to form the eutectic mixture.…”

“…On the other hand, the typically employed HBDs are organic acids, polyols, sugars and urea, among others [ 18 , 20 , 21 ]. These DES are widely used for extracting polyphenolic compounds [ 20 ], improving the extraction compared with commonly organic solvents [ 16 , 20 ], as they are rapidly prepared, easy to be stored, non-flammable, inexpensive, and present a high capacity of extraction for both polar and non-polar compounds [ 19 , 21 ]. There are different studies with some examples regarding the extraction of bioactive compounds from fruits using DES such as berry by-products [ 22 ], olive pomace [ 23 ], or apple pomace [ 24 ].…”

Comprehensive wheat straw processing with deep eutectic solvent to deliver reducing sugar and lignin streams

“…ChCl: acetic acid has a by almost 22°C melting point lower than pure ChCl or acetic acid, hence ChCl: acetic acid can be considered DES as reported in the literature [27]. This DES has been widely studied for the removal of phenolic compounds from several biomasses too [28][29][30][31]. However, studies for biomass deligni cation and conversion to reducing sugars are yet limited, speci cally for wheat straw biomass [18,32,33].…”