Extraction of chitin, preparation of chitosan and their structural characterization

International audienceChitin is a natural polysaccharide produced abundantly by biosynthesis in algae and fungi of the plant kingdom, as well as arthropods, mollusks, and other taxonomic groups of the animal kingdom. It consists of a sequence of monomers of N-acetylglucosamine and is found in three forms (α, β, and γ) which differ according to the arrangement of the chains in the crystalline region. Chitosan is the main high-value derivative of chitin. It is obtained by N-deacetylation reactions. Chitin and chitosan are copolymers consisting of units of N-acetylglucosamine and D-glucosamines linked by β- (1 → 4) glycosidic linkages. The major structural parameter is the degree of acetylation (DA), defined as the molar fraction of acetylglucosamine units. When the DA exceeds 50%, the copolymer is substantially insoluble in dilute acid solutions and corresponds to chitin. The chitosan name applies when DA is below 50%; the smaller the DA, the more soluble the copolymer is in acidic solutions. Methods for chitin and chitosan extraction from biomass are considered (Kurita, Broussignac, and laboratory processes) and compared to prepare samples with definite characteristics relative to the intended applications. The roles of the source (and the type of chitin) and the process will be discussed. Structural analysis will be presented to determine the DA using different techniques (spectroscopic, potentiometric, or conductimetric), which will be compared. The techniques to characterize the pattern of acetylation are discussed relative to the properties depending on this pattern. Finally, solution properties are addressed. Concerning these determinations and solution properties, special care must be taken to avoid macromolecular aggregates; this can be achieved by choosing appropriate solvents and solution concentration domains

Investigation of β-chitin extracted from cuttlefish: comparison with squid β-chitin

International audienceβ-chitins are extracted from two different parts of cuttlefish (Sepia officinalis officinalis) bone; the shell and the thin layer. They are then subjected to N-deacetylation reactions to prepare chitosans using the Broussignac or the Kurita process. The physicochemical characteristics of chitins and chitosans are compared to those obtained in the case of squid (Loligo vulgaris) β-chitin. In this work, the role of the source in determining the reaction behavior, during the extraction of chitin and the preparation of chitosan, is confirmed, although it is a β-chitin of two taxonomically close species. In particular, we show that the differences observed can be related to the differences in molar masses of the starting chitins, their crystallinity index and the rates of molecular degradation which accompany the N-deacetylation reactions. Finally, it was demonstrated that the huge quantities of bones rejected each year by the cuttlefish processing units from Dakhla city, alone, can be valorized by the production of about 77 tons of β-chitin that can be transformed into 60 tons of chitosan (presenting low degree of acetylation and molar masses ranging from 78,000 to 340,000 g/mol)

Fractional order prey-predator model with infected predators in the presence of competition and toxicity

In this paper, we propose a fractional-order prey-predator model with reserved area in the presence of the toxicity and competition. We prove different mathematical results like existence, uniqueness, non negativity and boundedness of the solution for our model. Further, we discuss the local and global stability of these equilibria. Finally, we perform numerical simulations to prove our results.</jats:p

Contribution to the preparation of chitins and chitosans with controlled physico-chemical properties

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