Smart advanced solvents for bioactive compounds recovery from agri-food by-products: A review

Highlights

• This review includes all the aspects of extraction of bioactives from agri-food wastes using smart solvents.

• Toxicity and recyclability of DESs and NaDESs are exhaustively reviewed.

• DESs and NaDESs are sustainable and safe solvents in the extraction of biomolecules.

• More research about the use of smart solvents to exploit of agri-food residues is necessary.

• The combination of DESs and NaDESs with intensive techniques improves extraction yields.

Abstract

Background

Worldwide, huge amounts of by-products and wastes are generated in agri-food sector annually. This biomass is usually discarded provoking serious environmental problems. However, these residues represent an excellent source of bioactive compounds so that their exploitation can be considered as a promising possibility from an economic and environmental perspective. Conventional extraction technologies using organic solvents have been employed to recover high-value molecules showing several drawbacks such as toxicity, high volatility and non-renewability. Therefore, the search of alternative green solvents for the extraction of bioactives and in order to reduce the environmental impact and to achieve a widespread consumer acceptance is mandatory. Recently, deep eutectic solvents (DESs) and natural deep eutectic solvents (NaDESs) have received great attention for their physicochemical features for bioactive compounds extraction.

Scope and approach

This review describes the state of the art of the applications of DESs and NaDESs in the field of the revalorization of agri-food by-products to obtain and isolate bioactive compounds. The synthesis and properties of these avant-garde solvents are described. In particular, the main bioactives extracted using DESs and NaDESs from several residues from citrus, winemaking, olive oil production, onion, seaweeds, animal and fish industries were systematically reviewed and collected.

Key findings and conclusions

DESs and NaDESs combined with emerging technologies to recover biomolecules from agri-food by-products show promising results in comparison with traditional methods of extraction using conventional solvents. These emerging solvents present advantages which make them good candidates for being implemented by the industry, considering their low toxicity, recyclability, tunable properties and environmentally friendly. Therefore, this new generation of solvents opens new options in the field of recovering bioactive compounds from agri-food by-products.

Introduction

The agri-food industry generates a vast amount of by-products which are considered as an important problem worldwide due to its damaging environmental impacts. This biomass is usually under valorized (Dedousi, Mamoudaki, Grigorakis, & Makris, 2017) despite several studies have suggested that it could be a remarkable source of a wide range of bioactive compounds (such as polyphenols, polysaccharides, pectin, anthocyanins, chitin, keratin, peptides, among others), which have been extensively studied for their health benefits, and anti-inflammatory, antimicrobial, antioxidant, and anticarcinogenic properties (Al Khawli et al., 2019; Borrajo et al., 2019; Echegaray et al., 2018; Grassino et al., 2018; Roselló-Soto et al., 2018, 2019; Gullón et al., 2017).

Taking into account the concerns about the improvement of the sustainability of the food industry and environmental problems involved in the management of these residues, there is a current growing interest in the valorization of these agri-food by-products to obtain valuable compounds (Barba et al., 2017; Gullón, Eibes, Moreira., Herrera, Labidi, & Gullón, 2018; Gullón, Gullón, et al., 2018). Nowadays, the revalorization of residual biomass from agri-food sector as a raw material for the production of novel commodities and biocompounds through biorefinery processes is considered pivotal for a sustainable growth based on a circular economy and as driving force for the implementation of “zero waste policies” (Athanasiadis, Grigorakis, Lalas, & Makris, 2017; Dedousi et al., 2017; Gullón et al., 2020). This type of processing introduces the concept of “grey” biorefinery and utilizes the food waste until its exhaustion to produce bioactive compounds in a similar way to how the fossil resources are processed in petroleum based refineries (Benvenutti, Zielinski, & Ferreira, 2019; Kamani et al., 2019).

In recent years, considerable efforts have been made to develop extraction methods for biomolecules recovery from agri-food wastes (Pal & Jadeja, 2019a; 2019b). These valuable compounds are usually obtained via conventional extraction processes using organic solvents such as acetone, hexane, methanol, ethanol, or ethyl acetate. However, the conventional solvents present several drawbacks such as toxicity, volatility and flammability limiting their application in the extraction of natural compounds (Benvenutti et al., 2019; Liu et al., 2018). In this framework, the agri-food industries must face the great challenge to adopt sustainable process strategies through the employment of emerging green technologies, decreasing at the same time the environmental deterioration and improving the process performance for transforming agri-food wastes into products with marketable value (Jiang et al., 2018; Putnik et al., 2017).

In this context, a new generation of solvents known as Deep Eutectic Solvents (DESs) including Natural Deep Eutectic Solvents (NaDESs) have been delineated as sustainable and safe solvents to replace conventional organic solvents in the extraction of bioactive compounds due to their excellent biocompatibility and low toxicity that make them suitable for pharmaceutical, cosmetic, agrochemical, and food applications. Furthermore, these solvents possess the stabilizing capacity of the extracted solutes possibly due to the formation of hydrogen bonds between solutes and DESs/NaDESs (Fernández, Espino, Gomez, & Silva, 2018), a clear advantage over those conventional solvents.

Moreover, the DESs and NaDESs have also been displayed to have high potential as solvents in combination with innovative and alternative technologies of extraction namely: ultrasounds, microwaves, pressurized liquid extraction (PLE) and homogenate-assisted extraction (HAE) (Benvenutti et al., 2019). These innovative extraction technologies present competitive advantages over the conventionals such as the reduction of operation time, decrease the volume of used solvent, saving the operation cost, and keeping the quality of the target molecules. For these reasons, they are considered as green extraction technologies. The combination of these avant-garde solvents with intensive extraction techniques also allows the improvement of extraction yields, which is attributed to the heat generated by ultrasounds and microwaves decreasing the solvent viscosity and enhancing the penetration of DESs and NaDESs into the biomass matrix (Mišan et al., 2019). However, despite the advantages of the combination of these emerging technologies with smart solvents, until date scarce data have been reported about its use to extract natural products from agri-food by-products.

Despite the literature collects several works about the use of DESs and NaDESs as solvents to recover biomolecules from natural sources, studies using these cutting-edge solvents for the exploitation of agri-food industry derived-residues is limited and this topic still has not been compiled in a review. Therefore, recent researches about the valorization of several agri-food wastes including those generated in citrus processing, winemaking, olive oil production, onion, seaweeds, animal and fish industries using DESs or NaDESs are approached in the present review. Their properties, synthesis, toxicity and recyclability are described focusing on the target compounds, as well as the main factors involved in the extraction process. In addition, the main agri-food industries that generate interesting sources of bioactive compounds are identified and the main results are described. Final remarks and a schematic overview related to bioactive compounds extraction by DESs or NaDESs (Fig. 1) are also included.