Optimization of deacetylation in the production of chitosan from shrimp wastes: Use of response surface methodology R.F. Weska, J.M. Moura, L.M. Batista, J. Rizzi, L.A.A. Pinto * Unit Operations Laboratory, Department of Chemistry, Fundac ¸a ˜o Universidade Federal do Rio Grande – FURG, Rua Engenheiro Alfredo Huch, 475, CEP 96201-900 Rio Grande, RS, Brazil Available online 15 December 2006 Abstract The use of chitosan in diverse areas is directly related to the polymer’s molecular weight and degree of deacetylation, which depends on the conditions of chitin deacetylation. The aim of the present study consisted of optimization of the deacetylation stage in the pro- duction of chitosan, using the response surface methodology for the polymer’s molecular weight. Chitin was obtained from shrimp wastes and the study of deacetylation made through a factorial experimental design, where temperature and time were varied. The esti- mate of chitosan’s intrinsic viscosity was made by linear regression with the values of reduced viscosity and concentration, using Huggins equation for polymers. The viscosity average molecular weight of chitosan was calculated for each experiment by the equation by Mark– Houwink–Sakurada that relates the intrinsic viscosity to the polymer’s molecular weight. The optimum condition for the deacetylation reaction for molecular weight was observed at a temperature of 130 °C and in 90 min, and corresponded to a molecular weight of chito- san of about 150 kDa, and a deacetylation degree of 90%. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Chitosan; Deacetylation; Experimental design; Molecular weight 1. Introduction Chitosan, b-(1 ! 4)D-glucosamine, is a partially deacet- ylated form of chitin, b-(1 ! 4)N-acetyl-D-glucosamine, a substance found naturally in the exoskeletons of insects, shells of crustaceans, and fungal cell walls (Ravi Kumar, 2000). Chitin can be converted into chitosan by enzymatic means or alkali deacetylation, this being the most utilized method. During the course of deacetylation, part of polymer N-acetyl links are broken with the formation of D-glucosamine units, which contain a free amine group, increasing the polymer’s solubility in aqueous means (Chen & Tsaih, 1998). The variations in preparation methods of chitosan result in differences in its deacetylation degree, the distribution of acetyl groups, the viscosity and its molecular weight (Berger et al., 2005; Chen & Hwa, 1996). These variations influence the solubility, antimicrobial activity among other properties, being that commercial chitosan usually has a deacetylation degree varying from 70% to 95%, and a molecular weight ranging from 50 to 2000 kDa (Rege, Gar- mise, & Block, 2003). Chitosan has many applications in agriculture, medi- cine, environment and food. However, in some fields, espe- cially in medicine and the food industry, the application of this polysaccharide is limited by its high molecular weight resulting in its low solubility in aqueous media (Ilyina, Tik- honov, Albulov, & Varlamov, 2000). Chitosan is used in food as clarifying agent and enzymatic browning inhibitor in apple and pear juices and in potatoes, and as antioxidant in sausages. Chitosan can also be used as an antimicrobial film to cover fresh fruits and vegetables (Devlieghere, Ver- meulen, & Debevere, 2004). Chitosan’s molecular weight distribution is influenced by factors such as time, temperature, reagent’s concentration 0260-8774/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2006.02.006 * Corresponding author. Tel.: +55 53 3233 8648; fax: +55 53 3233 8745. E-mail address: dqmpinto@furg.br (L.A.A. Pinto). www.elsevier.com/locate/jfoodeng Journal of Food Engineering 80 (2007) 749–753