Active chitosan–polyvinyl alcohol films with natural extracts

Abstract

Active films were prepared from chitosan (Ch) and polyvinyl alcohol (PVA) containing aqueous mint extract (ME)/pomegranate peel extract (PE). The effect of these extracts on the physical, mechanical, antimicrobial and antioxidant properties of the films were studied. Increased protection against UV light was observed in the films containing the extracts. Addition of ME/PE improved the tensile strength of the films without affecting their puncture strength. Ch–PVA films incorporated with PE had the highest tensile strength (41.07 ± 0.88 MPa). Permeability characteristics of the films were not altered due to addition of extracts. ME/PE conferred antioxidant properties to Ch–PVA films as determined by DPPH radical scavenging activity. The films also exhibited antibacterial activity against Staphylococcus aureus and Bacillus cereus. PE containing films totally inhibited the growth of B. cereus and reduced the number of S. aureus by 2 log cycles. These results suggest that Ch–PVA film containing ME/PE can be used for development of active food packaging materials.

Introduction

Packaging is an important factor in food industry and is dominated by petroleum-derived polymers. However, the amount of research involving the production and characterization of biodegradable films has increased substantially, mainly due to interest in minimizing the ecological impact caused by the use of synthetic packaging materials. Several biopolymers have been exploited to develop eco-friendly food packaging materials (Siracusa, Rocculi, Romani, & Rosa, 2008). A significant proportion of research on these films has been made using biopolymers from renewable sources, i.e. products or by-products derived from agriculture or from agro-industries. Usually, films based on biopolymers are highly sensitive to environmental conditions and generally present low mechanical resistance. As a result, several researchers have developed films based on mixtures of biopolymers and synthetic polymers (Ghorpade, Gennadios, Hanna, & Weller, 1995).

Chitosan (Ch) is a very promising biopolymer because it is environmentally friendly due to its biodegradability and has good film forming properties. In the food industry, Ch films promise immense potential to be used as active packaging material due to its antimicrobial activity, non-toxicity and low permeability to oxygen (No, Meyers, Prinyawiwatkul, & Xu, 2007). Some synthetic polymers from non-renewable sources are also biodegradable, such as polyvinyl alcohol (PVA). PVA is a synthetic, water soluble polymer with excellent film forming, emulsifying, and adhesive properties. It also imparts good tensile strength (TS) and biodegradability and hence has been used in many biomaterial applications. PVA has also been approved for use in packaging meat and poultry products by the USDA (DeMerlis & Schonek, 2003). Ch contains free hydroxyl and amine groups, and is therefore miscible with PVA due to the formation of hydrogen bonds.

Polymer blending is one of the most effective methods to have new material with desired properties. Films formed by blending of polymers usually results in modified physical and mechanical properties compared to films made of individual components. Since synthetic polymers are easily obtained and have low production cost, blending of natural and synthetic polymers improves the cost–performance ratio of the resulting films. Blending of synthetic polymers, such as PVA (Bahrami, Kordestani, Mirzadeh, & Mansoori, 2003), polycaprolactone (Sarasam, Krishnaswamy, & Madihally, 2006) with Ch have been reported to improve mechanical properties of Ch films. In order to enhance utility of these films, addition of active agents is being investigated to improve food safety and quality. In terms of active agents that can be incorporated into films, plant extracts have received much attention as they contain high concentrations of phenolic compounds that possess strong antioxidant properties. Earlier studies in our laboratory have shown that mint extract (ME) and pomegranate peel extract (PE) have good antioxidant potential (Kanatt, Chander, & Sharma, 2007, 2010). These extracts effectively scavenged DPPH, hydroxyl and superoxide radical and their scavenging ability was comparable to the synthetic antioxidant, butylated hydroxytoluene (BHT). ME/PE also had good reducing power and iron chelation capacity. Hence, the objective of this study was to develop composite active films from Ch and PVA incorporated with ME/PE. Optical, mechanical, barrier, antioxidant and antimicrobial properties of these films were also investigated.