Low-Phytotoxic Deep Eutectic Systems as Alternative Extraction Media for the Recovery of Chitin from Brown Crab Shells

Abstract

The versatility of chitin and its derivatives has allowed their utilization in a wide range of applications, from wastewater treatment to pharmaceutical or biomedical industries. However, even though the extraction method used industrially is extremely efficient, it involves the use of strong acids and bases and results in the disposal of large quantities of toxic effluents. Deep eutectic systems (DESs) have emerged as a promising new class of alternative solvents, including for chitin recovery. Yet, the assessment of their toxicity has often been neglected. Therefore, in this work, the phytotoxicity of choline chloride (ChCl)/organic acid-based DESs toward wheat seeds was evaluated by measuring different growth parameters and stress biomarkers. DESs were then explored for the efficient recovery of chitin contained in brown crab shell residues at varying conditions of temperature and processing time as well as with and without water addition. The obtained chitin was then characterized through different analytical techniques and compared to a standard as well as to chitin obtained by a conventional acid/alkaline hydrolysis. Results have shown that by applying a ChCl/lactic acid-based DES (which was the system that showed the least phytotoxic effects on wheat; EC50 ≥ 1.6 mg/mL) at 130 °C, it was possible to obtain pure chitin (up to 98%) with characteristics similar to those presented by commercial chitin or chitin recovered by conventional hydrolysis in a shorter time (more than 8-fold faster), thus suggesting that ChCl/organic acid-based DESs can truly represent a low-phytotoxic alternative extraction media for the recovery of chitin from the crab shell biomass.

Chitin, Chitosan, and Nanochitin: Extraction, Synthesis, and Applications

“…In pursuit of lower toxicity, natural deep eutectic solvents (NADESs) were developed; NADESs are composed of primary metabolites and offer a lower-cost, biodegradable option for the extraction of biomass [ 42 , 44 , 45 ]. Among NADESs used for chitin extraction, choline chloride (ChCl)/organic acid combinations are the most common due to their low toxicity and ability to remove calcium carbonate; betaine is another common hydrogen bond acceptor, and hydrogen bond donors include organic molecules such as glycerol, ethylene glycol, and urea [ 12 , 13 , 46 , 47 ]. Saravana et al tested deep eutectic solvents composed of choline chloride and various other components such as organic acids and alcohols for their ability to extract chitin from shells of the shrimp species Marsupenaeus japonicus [ 31 ].…”

“…Higher yields were obtained with the NADES compared to an acid/alkali method, though the acid/alkali method was more effective at removing shell minerals and proteins [ 31 ]. To work around the relatively limited ability of NADESs to remove proteins shell minerals, Rodrigues et al added water to the NADES/chitin solution after the extraction step and stirred for 30 min [ 46 ]. This both precipitated the chitin out of the NADES solution and generated an acidic environment to facilitate the removal of shell minerals and hydrolysis of proteins [ 46 ].…”

“…To work around the relatively limited ability of NADESs to remove proteins shell minerals, Rodrigues et al added water to the NADES/chitin solution after the extraction step and stirred for 30 min [ 46 ]. This both precipitated the chitin out of the NADES solution and generated an acidic environment to facilitate the removal of shell minerals and hydrolysis of proteins [ 46 ]. Adding a decolouration step with hydrogen peroxide produced chitin with up to 98% purity with one third of the losses associated with the acid/alkali method [ 46 ].…”

“…This both precipitated the chitin out of the NADES solution and generated an acidic environment to facilitate the removal of shell minerals and hydrolysis of proteins [ 46 ]. Adding a decolouration step with hydrogen peroxide produced chitin with up to 98% purity with one third of the losses associated with the acid/alkali method [ 46 ]. Use of microwave radiation has also been indicated to improve the demineralization and deproteination capabilities of DESs; in a study by Huang et al, it was found that more than 99% of minerals were removed from shrimp shells after 9 min of irradiation and that deproteination improved with a higher NADES/shell ratio up to the maximum 20:1 [ 48 ].…”

An Overview on Phytotoxic Perspective of Ionic Liquids and Deep Eutectic Solvents: The Role of Chemical Structure in the Phytotoxicity

“…Greater reduction of chlorophyll content was observed by ChCl.OA compared to ChCl.Gly and ChCl.Glc [130]. Rodrigues et al [131] studied the phytotoxic effect of choline based DESs against wheat seeds by studying various growth parameters and stress biomarkers. Different DESs were prepared by mixing ChCl with malonic acid, malic acid, and lactic acid.…”