DEVELOPMENT OF THE NOVEL ACTIVE PACKAGING FILM PREVENTING MIGRATION OF ANTIMICROBIAL COMPONENT

Rivka Cahana, Vadim Goldsteinb, Binjamin Finkelsteinb, Edward Bormashenkoa

aThe College of Judea and Samaria, The Research Institute, 44837, Ariel, Israel

bActipol LTD, 12900, Katzrin, Israel

ABSTRACT. The paper presents new antimicrobial active packaging intended to improvement of safety and quality of food, as well as to extending its shelf -life. We tried to develop active packaging material in which migration of the antimicrobial ingredient would be hindered by special preliminary treatment, performed according to guest-ligand technology. In this research we investigated the effect of thermoplastic film mixed with antiseptic material (starch potato, polyacrylamid and mercaptobenzothiazol) on bacterial growth. Thermoplastic film was introduced to Bacillus cereus culture. The culture was grownat 37ºC in NB broth. We studied the rate of the culture growth and it was revealed that the antimicrobial film inhibited growth of the culture up to 50-70% comparatively to the control culture after 3-4 hours of observation.

1. Introduction

Foods are spoiled by a variety of both bacteria and fungi, but only particular microorganisms typically attack each type of food. This is because the chemical properties of foods vary widely, and different foods are colonized by the indigenous spoilage organisms that are best able to utilize the nutrient. In general, microorganisms grow on food surfaces thereby development of active packaging where the antibacterial agent is immobilized tightly, will be the answer to consumers’ demand for food without preservatives.

The traditional passive packaging is restricted in protecting food products because of the way that food is distributed and stored. Furthermore, the extended shelf -life of manufactured foods and the consumers demand for minimal additions of preservatives to food products have lead to the innovation of active packaging. Major active packaging technologies that exist based on use of: oxygen scavengers, moisture regulators, ethylene absorbers, taint removal, ethanol and carbon dioxide emitters as well as antimicrobial systems [1]. The antimicrobial active packaging technology based on antimicrobial agents that are immobilized with the polymeric structure or incorporated in plastic resins, before film casting. This technology can be divided into two types: preservatives that are released slowly from the packaged materials to the food surface or preservatives that are firmly fixed and do not migrate into the food products. Both are assumed to control growth of undesirable microorganisms.

Among the common microorganisms that contaminate food and drink products are E.coli, Staph. aureus, Campylobacter, Salmonella, Clostridium perfringens andBacillus cereus. Toxins produced by microorganisms or growth of microorganisms in the human body after the contaminated food has been eaten cause food poisoning. There are few chemical antimicrobial agents that are used commercially to control microbial growth in foods [2-5].

Many of these chemicals, like sodium propionate, have been used for many years with no indication of human toxicity. Others, like nitrites, ethylene or propylene oxides, are more controversial antimicrobial control because of evidence that these agents are harmful to human health. In recent years there are several reports of using bacteriocins, proteins that possess antimicrobial activity, and are produced by microorganisms, as food preservatives [4]. Development of different kinds of active packaging is under intensive progress now [6-7]. One of the key problems of the active packaging technologies resides in the controlled release of the antimicrobial agent from the polymer film [8]. However as yet very limited published works are available in the area.

Polyethylene and its copolymers are much popular materials for food packaging but they don’t hold molecules of additives for a long time. At the same time it is well-known fact that polyethylene and its copolymers form clathrates (complex compounds) with organic compounds containing active functional groups. We proposed to treat antimicrobial additive according to guest-ligand technology (in our case antimicrobial additive is a guest), and to form clathrates dispersed uniformly in polymer matrix will provide controlled release of active additive in time. Our paper presents very preliminary results of the testing of antimicrobial activity of polyethylene copolymer films containing antimicrobial clathrates.

In the USA, Japan and Australia, active packagings already exist. However, in Europe, due to strict legislative, active packaging systems have been restricted so far.

2. Experimental

2.1 Obtaining of antimicrobial film

Copolymer ethylene-vinyl acetate (EVA) was used a matrix material. Chemical structure of EVA is presented below:

EVA copolymer is distinguished by its high clarity, puncture-resistance, impact strength and low heat-seal temperature. These properties make EVA a superior resin for many high performance flexible packaging applications [9]. We used EVA copolymer with melting index 2.5 g/10 min, suitable for blown film extrusion.

The process of film preparation is presented in Fig. 1. 1 wt.% per cent of preliminary treated antimicrobial additives were mixed with polyethylene wax PW-300 under temperature 100 ºC, then mixture was cooled and pelletized granules of the mix were introduced into single-screw extruder Econ-Film, manufactured by “Plastengineering Knauff LTD”, equipped by blown film die, and film stretching unit. Parameters of the extruder: diameter of the screw: 30 mm, L/D = 26. Temperature regime of extrusion: T1=120 ºC, T2=125 ºC, T3=140 ºC, T4=155 ºC, N = 55 rpm.

2.2. Measurement of antimicrobial activity.

An overnight Bacillus cereus culture in nutrient agar pH 7 (Difco. USA) was transferred into fresh nutrient broth medium (final volume, 30 ml), pH 6.5. The cultures were grown with or without EVA film mixed with the antimicrobial agent, at 37°C with aeration. Optical density was determined at intervals of 30 min, at 660 nm with Jenway 6300 spectrophtometer.

3. Results and discussion

The main problem, which we tried to solve could be formulated in such a way is it possible to keep antimicrobial properties of the film and to prevent migration of the antimicrobial agent simultaneously? Does antimicrobial agent keep its activity after formation of the clathtate complex?

In our study we introduced the antimicrobial agent (Mercaptobenzothiazol, Polyacrylamidand starch potato) into EVA film. Bacillus cereusculture have been grown on N.B with or with out EVA film mixed with antimicrobial agent, and it was shown that under 3-4 hours of observation, bacterial growth in the culture, grown in the presence of the film has been reduced to about 50-70% comparatively to the those of untreated culture.

References

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Fig. 1

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