Effect of genipin cross-linking on properties of chitosan based bio-composite film

Abstract

Active packaging from chitosan film incorporated with astaxanthin is limited commercial application in the food industry due to its high moisture permeability and poor tensile strength. To overcome these problems, crosslinking of the film with genipin and heat curing to improve film properties were proposed. Firstly, the effects of genipin concentration on the physical, moisture barrier and mechanical properties of chitosan films incorporated with astaxanthin were investigated. Chitosan film was prepared by mixing chitosan in 2% (w/w) lactic acid. The chitosan was incorporated with astaxanthin at 0 and 1% (w/w of chitosan) (marked as CS and CA or CSA) and crosslinked with genipin at various concentrations including 0.5, 1.0 and 1.5% (w/w of chitosan) (marked as CS0.5G, CS1G, CS1.5G, CSA-0.5G, CSA-1G or CAG and CSA-1.5G). The chemical crosslinking structure, crosslinking degree, water vapor permeability, mechanical properties, oxygen permeability, color, thermal stability, crystallinity and surface characterization of the films were investigated. The results showed that an increase in genipin concentration increased crosslinking degree, as confirmed by Fourier transform infrared spectroscopy showing that there were interactions between chitosan and genipin. Increasing the concentration of genipin significantly decreased water vapor permeability (WVP), crystallinity and elongation at break (EAB) while tensile strength (TS), Young’s modulus (YM), thermal stability and oxygen permeability increased. The surface characteristic of the films was observed by scanning electron microscopy (SEM) and it was found that crosslinked film had rougher surface than non-crosslinked film. Since chitosan crosslinked with 1.5% genipin film (CS1.5G) and chitosan-astaxanthin film crosslinked with 1% genipin (CAG) showed optimal properties (WVP, TS and YM), CS-1.5G and CSA-1G films were used further to study the effect of heat curing temperature.

The second study aims to evaluate the influence of curing temperature on chemical-crosslinking and properties of the films. The CS, CS-1.5G, CSA and CAG films were cured at 25 (marked as CS-25, CS1.5G-25, CSA-25 and CAG-25, respectively), 80 (marked as CS-80, CS1.5G-80, CSA-80 and CAG-80, respectively) and 105°C (marked as CS-105, CS1.5G-105, CSA-105 and CAG-105, respectively) for 30 min. The films were analyzed for WVP, contact angle, chemical structure, TS, EAB, YM and thermal stability. The results showed that CS1.5G and CAG films cured at 105°C had the lowest (p<0.05) WVP value which by decreased by 54-55% while the contact angle increased, when compared to CS-25 and CSA-25 film. Heat curing increased the chemical interaction between C-C double bond of genipin already linked with chitosan chain. These results led to an improvement of TS and YM by 55-60% and 42-50%, respectively for CS1.5G-105 and CAG-105 films. Moreover, thermal stability of CS1.5G-105 and CAG-105 films were enhanced and the resulting films can lower light transmission through film. The results suggested heat curing can improve the properties of genipin-crosslinked chitosan-based film which has potential to be used for active food packaging applications. Moreover, since genipin is a nontoxic natural crosslinker, the developed film is considered safe to use with food.

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