Elsevier

Food Hydrocolloids

Volume 24, Issue 8, November–December 2010, Pages 770-775
Food Hydrocolloids

Physical properties and antioxidant activity of an active film from chitosan incorporated with green tea extract

https://doi.org/10.1016/j.foodhyd.2010.04.003Get rights and content

Abstract

An active film from chitosan incorporated with aqueous green tea extract (GTE) was developed. The effects of GTE concentrations including 2, 5, 10 and 20% (w/v) of green tea in the film-forming solution on the film properties were determined by measuring physical properties, total polyphenolic content and antioxidant activity of the active films. Fourier Transform Infrared (FTIR) spectrometry was carried out to observe the potential modifications of the chitosan films when incorporated with GTE. The results suggested that incorporation of GTE into chitosan films improved mechanical and water vapor barrier properties and enhanced polyphenolic content and antioxidant activity of the films. Changes in the FTIR spectra of the chitosan films were observed when GTE was incorporated, suggesting some interactions occurred between chitosan and the polyphenols from GTE. This study showed the benefits of incorporation of GTE into chitosan films and the potential for using the developed film as an active packaging.

Introduction

Consumer concerns of food quality and safety lead to the development of active packaging, which is an innovative packaging performing some functions in the preservation of the food other than providing a barrier property. Active compounds and ingredients can be incorporated into packaging materials to provide several functions that do not exist in conventional packaging systems. Active packaging may carry antioxidants, antimicrobial agents and/or nutrients. Moreover, due to the health concerns of the consumers and environmental problems, current research in active packaging has focused on the use of natural preservatives in biodegradable packaging materials (Suppakul et al., 2003, Yingyuad et al., 2006).

Chitosan, a linear polysaccharide of randomly distributed β-(1-4)-linked D-glucosamine and N-acetyl-D-glucosamine, is a deacetylated product of chitin and is considered a biobased environmentally friendly material (Caner and Cansiz, 2007, Fernandez-Saiz et al., 2009). Chitosan has potential to be used as alternative resources for active food packaging. Chitosan has intrinsic antioxidant and antimicrobial properties, which are affected by its molecular weight and concentration. Chitosan has been used as antimicrobial films and coatings due to its effectiveness of inhibiting the growth of not only Gram-positive and Gram-negative bacteria but also yeasts and moulds. Chitosan antimicrobial activity comes from its positive charges that would interfere with the negatively charged residues of macromolecules on the microbial cell surface, causing the membrane leakage (Caner and Cansiz, 2008, Dutta et al., 2009, Fan et al., 2009, Hernández-Muñoz et al., 2008).

Incorporation of antioxidants into packaging materials has become popular since oxidation is a major problem affecting the food quality. Currently, the most frequently used antioxidants in active packaging are butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). Although these synthetic antioxidants can effectively be used in active food packaging because of high stability, low cost and efficiency, there are significant concerns related to their toxicological aspects. Moreover, use of synthetic antioxidants is under strict regulation due to the potential health risk caused by such compounds. Therefore, extensive research has been conducted to employ some natural antioxidants such as phenolic compounds as alternatives to synthetic antioxidants (Chan et al., 2007, Jongjareonrak et al., 2008, Yen et al., 2008). Current research concerning use of natural antioxidant in edible films includes the addition of vitamin E into chitosan-based film (Park & Zhao, 2004) incorporation of tetrahydrocurcuminoids into chitosan film (Portez, Gardrate, Catellan, & Coma, 2009) and use of antioxidant borage extract in gelatin film (Gómez-Estaca, Gimnez, Montero, & Gómez-Guillén, 2009).

Green tea (Camellia sinensis), nonfermented products, is a good source of polyphenolic compounds having strong antioxidant property (Chan et al., 2007). The important polyphenolic compounds in tea leaves include catechin, theaflavins and thearubigins (Gramzaa et al., 2006). Green tea catechins, including (−)-epicatechin (EC), (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin gallate (EGCG), (−)-catechin (C), (−)-gallocatechin gallate (GCG), (−)-catechin gallate (CG), and (−)-gallocatechin (GC), are proved to exhibit antimicrobial activity against some bacteria and have good antioxidant activity. The beneficial effects of the phenolic compounds are thought to result from their ability to scavenge reactive oxygen and nitrogen species (Chan et al., 2007, Rohn et al., 2004). Green tea has been reported to delay the onset of lipid oxidation in various foods including marine oil (Wanasundara & Shahidi, 1998), soybean oil and corn oil (Yanishlieva & Marinova, 2001) and dry-fermented sausage (Bozkurt, 2006).

As mentioned earlier, biodegradable active packaging is the main focus of current food packaging research and developments. Chitosan is a functional biopolymer, having intrinsic antimicrobial and antioxidant properties and consequently has high potential to be used as a biodegradable active packaging. Although, chitosan has antioxidant property, there are some limitations in being a practical antioxidant. The possibility to improve antioxidant property of the chitosan film is to incorporate with antioxidant agents. As a good source of polyphenols, GTE may be used as active agent and incorporated into film. Accordingly, the aim of this research was to develop an environmentally friendly active film from chitosan incorporated with aqueous green tea extract as a natural antioxidant. To determine if the developed film would have potential to be used as an active packaging, water vapor permeability, mechanical properties, total phenolic content and antioxidant activity of the films were evaluated.

Section snippets

Film preparation

Green tea leaves were purchased from a local hypermarket in Bangkok and ground using a blender (Toshiba MX-X10GMC, Toshiba Thailand Co., Ltd., Bangkok, Thailand). Green tea powders were kept in a linear low density polyethylene laminated aluminium pouch under vacuum condition using a vacuum packaging sealer (WEBOMATIC, Bochum, Germany) and stored at 8 °C, until extraction. Green tea water extract solution was prepared by mixing ground tea powder in distilled water (1:5 w/w) controlled at 90 °C in

Film color and opacity

The effects of GTE concentration on film color and opacity are shown in Table 1. Adding GTE into chitosan films significantly affected (p  0.05) L (lightness/darkness), a (redness/greenness) and b (yellowness/blueness) values of the film surface. Films without GTE were lighter (higher L value). L values of the films decreased from 87.50 ± 1.43 to 65.70 ± 0.97, but a increased from 1.11 ± 0.16 to 3.99 ± 0.28 (indicator of the tendency towards redness) and b values increased from 1.37 ± 0.1 to 40.02 ± 1.49

Conclusions

This study indicated that an active film from chitosan-based film could be achieved by incorporation with GTE, as a natural antioxidant. Addition of GTE improved mechanical, water vapor barrier and antioxidant properties of the resulting films. These changes, as verified by FTIR analysis, could be attributed to the interactions between functional groups of chitosan and GTE polyphenolic compounds. The chitosan film incorporated with GTE shows potential to be used as an active film. Nevertheless,

Acknowledgements

This research was fully supported by the Thailand Research Fund under funding No. RMU-5080063. The authors would like to thank Mr. Sarun Binmittor and Scientific & Technology Research Equipment Centre, Chulalongkorn University.

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