Preparation of chitosan films by neutralization for improving their preservation effects on chilled meat

Films prepared by natural polymers have received considerable attention, in recent years due to their biodegradable and environmentally friendly properties. Chitosan films were prepared by casting method and neutralization treatment with sodium hydroxide (NaOH) solution. An increase in mechanical property and a reduction in swelling property, water vapor permeability, and oxygen permeability were shown with increase of NaOH concentration and neutralization time. The chitosan film neutralized with 10% NaOH solution for 90 s had the best barrier performance against water and oxygen. Neutralization also allowed the formation of new hydrogen bonds in chitosan chains as the deprotonation of amino groups, which increased the compactness of chitosan films according to fourier transform infrared spectroscopy and x-ray diffraction analyses. Their preservation effects on chilled meat were further investigated in comparison with a plastic fresh-keeping film, low-density polyethylene (LDPE). Chitosan films could effectively preserve the chilled meat from lipid oxidation and microorganism propagation during 10 d storage, having lower drip loss, thiobarbituric acid reactive substances, aerobic plate count, pH, and total volatile basic nitrogen than the blank sample without packaging. Although the meat packed with LDPE film had the lowest drip loss value, its preservation effects on chilled meat were similar or even worse to the blank sample. The preservation effects of chitosan films on chilled meat were also improved as NaOH concentration and neutralization time increased due to the improvement in water and oxygen barrier properties, where the drip loss of chilled meat was reduced to effectively inhibit the oxidative deterioration and the growth of spoilage microorganisms. Therefore, chitosan film after neutralization can be used as a potential fresh-keeping film for chilled meat.