Abstract
Chitin is a structural polysaccharide of the cell walls of fungi and exoskeletons of insects and crustaceans. In this study, chitin was extracted, for the first time in our knowledge, from the Cicada orni sloughs of the south-eastern French Mediterranean basin by treatment with 1 M HCl for demineralization, 1 M NaOH for deproteinization, and 1% NaClO for decolorization. The different steps of extraction were investigated by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM). Results demonstrated that the extraction process was efficiently performed and that Cicada orni sloughs of the south-eastern French Mediterranean basin have a high content of chitin (42.8%) in the α-form with a high degree of acetylation of 96% ± 3.4%. These results make Cicada orni of the south-eastern French Mediterranean basin a new and promising source of chitin. Furthermore, we showed that each step of the extraction present specific characteristics (for example FTIR and XRD spectra and, consequently, distinct absorbance peaks and values of crystallinity as well as defined values of maximum degradation temperatures identifiable by TGA analysis) that could be used to verify the effectiveness of the treatments, and could be favorably compared with other natural chitin sources.
Highlights
Chitin is a copolymer of N-acetyl-d-glucosamine and d-glucosamine units linked with β-(1–4)glycosidic bond, composed predominantly of N-acetyl-d-glucosamine units and represents the second most abundant polysaccharide after cellulose [1]
The chitin can exist in three different forms: α, β, and γ-chitin that present an antiparallel, parallel, and alternated arrangements of polymer chains, respectively [14]. α-chitin is mostly found in fungi [15], arthropod exoskeleton, and shells of crustaceans [1], β-chitin is mostly found in squid pens [16], and γ-chitin is mostly found in the beetle family Lucanidae [17]
Biological extraction methods are based on the use of lactic acid-producing bacteria for the demineralization, thanks to the reaction of lactic acid with calcium carbonate and the subsequent formation of calcium lactate that can be removed by precipitation, while the deproteinization is mainly based on the use of proteolytic bacteria, which produce proteases that eliminate proteins [20]
Summary
Chitin is a copolymer of N-acetyl-d-glucosamine and d-glucosamine units linked with β-(1–4)glycosidic bond, composed predominantly of N-acetyl-d-glucosamine units and represents the second most abundant polysaccharide after cellulose [1]. The lost cuticle is mainly made of chitin, and of proteins and calcium carbonate, creating a rigid structure with the role of protecting the inner soft tissues from injury [13] These cuticles can represent a source of chitin. Several methods have been developed to extract chitin from different natural sources, generally following a common protocol: the elimination of minerals (demineralization), proteins (deproteinization), and pigments (decolorization) until the final product: the chitin. These extraction methods can have either a biological or chemical nature [19]. Chemical extraction methods are the most used in both industrial and laboratory production and involve an acid treatment, mostly with hydrochloric acid (HCl) ranging from 0.5 to 2 M, to dissolve the calcium carbonate (demineralization), followed by alkaline treatment with sodium hydroxide (NaOH)
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