Preparation, characterization and evaluation by FTIR and NMR of antimicrobial activity of chitosan active films

One of the main causes of food spoilage is the development of microorganisms. In order to inhibit or retard the growth of microorganisms and consequently, improve food security and extend the shelf life of food products, in the past years, active packaging and particularly films with antimicrobial properties have attracted the attention of the scientists. One of the approaches used is to add chitosan to the film. Due to their excellent properties, non-toxic, biodegradable, biofunctional and biocompatible with others antimicrobials, chitosan is one of the antimicrobial agents most appropriate for the development of active materials [1]. Chitosan (CAS nº 9012-76-4) is a polysaccharide, with the structure of a linear polymer of (1-4)-linked 2-amino-deoxy-β-D-glucan, obtained by the partial deacetylation of chitin, one of the most abundant polysaccharides in nature, found in shells of crustaceans [2]. Shrimp waste (heads and cephalothorax) samples were collected from local shrimp processing factories in South Sonora, Mexico. The waste was minced, fermented and centrifuged. After the treatment, three fractions were obtained: chitin rich fraction, protein rich liquor and lipid fraction. In this work, Fourier Transformed Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) were used to characterize three different samples of chitosan. Moreover, 100% chitosan-based films and films of polyamide with chitosan incorporated were also evaluated. The degree of acetylation (DA) values obtained may change, depending on the nature and level of impurities, source and polymer morphologies [3]. To evaluate the DA, FTIR and NMR were used. The samples were prepared as a thin pellet made from a mixture of KBr and the chitosan powder. To evaluate the DA in films, Fourier Transform Total Reflection infrared Spectroscopy (FTIR-ATR) was used. All spectra were recorded in the range of 400-4000 cm-1. Nuclear Magnetic Resonance (NMR) was also employed to evaluate the DA. Two experiments were tentatively carried out: 1H NMR and 13C NMR. In both cases approximately 5 mg of each sample were diluted in 1 % (v/v) CD3COOD in D2O. All data were compared with three commercially available standards submitted to the same experiments as samples. The sample 1 corresponding to chitosan obtained from shrimp waste and with high viscosity presented the lowest DA, therefore had higher antimicrobial activity. Both techniques; FTIR and NMR, led to the same conclusion.FONCICYT (Fund for International Cooperation of Science and Technology EU-Mexico