Novel Karaya Gum Derivatives Produced by Alkaline Hydrolysis and Periodate Oxidation for Active Packaging with Cinnamaldehyde

Abstract

This study aims to produce novel derivatives of karaya gum using chemical modification and then apply them for active packaging with cinnamaldehyde as the main active component. Native karaya gum (NKG) was hydrolyzed using sodium hydroxide to yield hydrolyzed karaya gum (HKG), which then was oxidized using sodium periodate to yield hydrolyzed-oxidized karaya gum (HOKG). For comparison, NKG was also directly oxidized using sodium periodate to produce oxidized karaya gum (OKG). FTIR spectra confirmed the removal of acetyl groups after alkaline hydrolysis and the formation of carbonyl groups with subsequent formation of hemiacetal and acetal structures after periodate oxidation. The alkaline hydrolysis and the periodate oxidation resulted in opposite effects on the hydrophilicity of the gum: hydrolysis increased solubility, moisture uptake, and viscosity, while periodate oxidation decreased these properties. We then produced films from corn starch and these gums (5% $w/w$ gum/starch) and properties of the films were studied. Hydrolysis of KG resulted in higher tensile strength, higher transparency but lower puncture strength and antifungal activity against of the films, while periodate oxidation exerted the opposite effects. The incorporation of 5% cinnamaldehyde ( $w/w$ of starch) exerted strong antifungal and antibacterial effects on the films against Colletotrichum gloeosporioides and Escherichia coli, which are useful in active packaging. The active packages based on the novel derivatives of KG can find applications in the agricultural, food, and pharmaceutical industries.