Published: July 26, 2011 r2011 American Chemical Society 3285 dx.doi.org/10.1021/bm200750t | Biomacromolecules 2011, 12, 3285–3290 ARTICLE pubs.acs.org/Biomac Structural Characterization of Chitin and Chitosan Obtained by Biological and Chemical Methods Neith Pacheco, † M onica Garnica-Gonzalez, † Miquel Gimeno, ‡ Eduardo B  arzana, ‡ St  ephane Trombotto, § Laurent David, § and Keiko Shirai* ,† † Universidad Autonoma Metropolitana, Biotechnology Department, Laboratory of Biopolymers. Av. San Rafael Atlixco No. 186. Col. Vicentina, C.P. 09340, Mexico City, Mexico ‡ Dpto. Alimentos y Biotecnología. Facultad de Química, Universidad Nacional Aut onoma de M exico, Ciudad Universitaria, M exico D.F., 04510, Mexico § Universit  e de Lyon, Universit  e Claude Bernard Lyon 1, Ing enierie des Mat  eriaux Polym eres (IMP) UMR CNRS 5223, 15 Bd Latarjet, 69622 Villeurbanne, Cedex France b S Supporting Information ’ INTRODUCTION Chitin, the poly(β-(1-4)-N-acetyl-D-glucosamine), and its deacetylated derivative chitosan are biorenewable, biodegrad- able, biofunctional, and nontoxic biopolymers with envisaged biomedical applications owing to their biological properties, such as in tissue engineering; wound healing, or excipients for drug delivery, among others. 13 Chitin is present in crustaceans as ordered crystalline microfibrils forming a complex structure with proteins, minerals, and lipids 4 and possesses three polymorphic forms (R, β, λ), where R is the most common structure, corresponding to a tightly compacted orthorhombic cell of alter- nate sheets of parallel and antiparallel chains. 5 In general, chitosans have lower molecular weights, and they are less crystalline than chitin precursors and thereby suitable candidates for chemical or physical modifications. 6 Commercial chitin is effectively isolated from crustacean shells after chemical treatments; 1 however, these methodologies do not allow for the recovery of added value and sensitive byproducts such as protein hydrolyzates and pigments. 79 Moreover, the chemical procedures imply the generation of undesirable corrosive side products and reduction in chitin molecular weights. 2 Alternatively, biological approaches for chitin recovery have been proposed, 7,10,11 and among them, lactic acid fermentations (LAFs) are promising because minerals (calcium carbonate) are solubilized in situ and endogenous pro- teases are adequately activated for deproteinization. 7,8,12 Regarding chitosan, the conditions employed for deacetyla- tion of chitin, such as temperature, alkali concentration, time, and raw material properties, affect its properties and consequently its further applications. 1,13 Chemical deacetylation conducted un- der heterogeneous conditions at high temperature during a short period of time is faster in amorphous regions, 14,15 whereas homogeneous deacetylation, at relatively low temperatures and extended time, results in random distribution of deacetylated residues in the polymer backbone. In both cases, high deacetyla- tion can be successfully achieved but with remarkable reduction in molecular weight. 1,14 It has been suggested that the initial crystalline structure of the chitin is an important parameter during deacetylation and affects final chitosan structure as well Received: June 2, 2011 Revised: July 22, 2011 ABSTRACT: Chitin production was biologically achieved by lactic acid fermentation (LAF) of shrimp waste (Litopenaeus vannameii) in a packed bed column reactor with maximal percentages of demineralization (D MIN ) and deproteinization (D PROT ) after 96 h of 92 and 94%, respectively. This procedure also afforded high free astaxanthin recovery with up to 2400 μg per gram of silage. Chitin product was also obtained from the shrimp waste by a chemical method using acid and alkali for comparison. The biologically obtained chitin (BIO-C) showed higher M w (1200 kDa) and crystallinity index (I CR ) (86%) than the chemically extracted chitin (CH-C). A multistep freezepumpthaw (FPT) methodology was applied to obtain medium M w chitosan (400 kDa) with degree of acetylation (DA) ca. 10% from BIO-C, which was higher than that from CH-C. Additionally, I CR values showed the preservation of crystalline chitin structure in BIO-C derivatives at low DA (4025%). Moreover, the FPT deacetylation of the attained BIO-C produced chitosans with bloc copolymer structure inherited from a coarse chitin crystalline morphology. Therefore, our LAF method combined with FPT proved to be an affective biological method to avoid excessive depolymerization and loss of crystallinity during chitosan production, which offers new perspective applications for this material.