Chitosan-gallic acid films as multifunctional food packaging

Chitosan is a good candidate for multifunctional food packaging because of its biocompatibility, biodegradability, antibacterial properties, secondary antioxidant activity, film forming ability, resistance to lipids and because of its structure which is very desirable for grafting various compounds to it. For this research, we took advantage of chitosan’s amino group that has nuceleophilic character at a pH above its pKa, which is 6.3. Gallic acid, a phenolic compound with primary antioxidant properties was grafted to chitosan using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide. Grafting was evaluated using FTIR-ATR and 1H and 13CNMR. FTIR showed evidence of grafting on the amino group by differences of amide stretching in grafted chitosan (grafted) as compared to a mixture of chitosan and gallic acid, and non- modified chitosan. However, NMR results were inconclusive. Grafted chitosan showed significant primary antioxidant activity, containing 34.26 mg gallic acid/g, had DPPH scavenging ability of 90%, reducing power of ABS700=0.5, and was soluble in aqueous acetic acid. The grafted chitosan readily formed films possessing excellent puncture strength and stability, evidenced by stable antioxidant activity over a 15 week storage period at 50°C. When evaluated as packaging material for peanuts, the films reduced malondialdehyde, peroxide and conjugated triene formation as compared to polyethylene bags. The grafted films also possessed antibacterial properties, showing a 2-log reduction of Salmonella Typhimurium. The grafted films were evaluated as packaging for potato chips and compared with mixed chitosan and gallic acid films, on modified chitosan films and Ziploc® bags. The grafted chitosan pouches significantly reduced lipid oxidation throughout 8 weeks of storage at 50°C compared to Ziploc® pouches. Mixed chitosan and gallic acid pouches and films had similar properties to those exhibited by grafted films. Therefore, chitosan films prepared with free or grafted gallic acid have been demonstrated to be potentially valuable multifunctional food packaging. Chitosan films with the primary antioxidant properties of gallic acid show promise for multifunctional food packaging