Introduction of primary antioxidant activity to chitosan for application as a multifunctional food packaging material

• Grafting of gallic acid introduced primary antioxidant properties to chitosan.
• Physical characteristics of chitosan films were not altered by gallic acid grafting.
• Films formed of gallic acid grafted chitosan slowed oxidation of packaged peanuts.

The objective of this study was to improve functionality of chitosan films by introducing the primary antioxidant property to chitosan molecule. Grafting of gallic acid (GA) on chitosan was most efficient when chitosan, GA, carbodiimide, and N-hydroxysuccinimide were used in the ratio 2·10−4:1:0.05:0.05. There was no significant difference in grafting efficiency when the reaction lasted 6 or 24 h. Chitosan with 80% degree of deacetylation (DDA) was efficiently grafted and increase in DDA did not improve grafting. Non-grafted, native chitosan had insignificant 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging ability (9.4%) and no reducing power. The GA-grafted chitosan had 34.26 mg GA/g, DPPH scavenging ability of 89.5%, reducing power of A700 = 0.51, and was soluble in aqueous acetic acid. During storage of ground peanuts under stress conditions (50 °C, 20–30% RH), both chitosan and GA-chitosan pouches provided significant reduction in oxidation reactions. Furthermore, the GA-grafted chitosan reduced level of thiobarbituric acid reactive substances (TBARS), peroxide, and conjugated trienes formation as compared to polyethylene bags. GA-grafted chitosan shows promise as a candidate for multifunctional food packaging material.

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