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Packaging containing natural antimicrobial or antioxidative agents
Packaging containing natural antimicrobial or antioxidative agents Dong Sun Lee
introduction Antimicrobial packaging Antioxidative packaging Future potential References
108 110 116 118 119
Introduction The most frequent mechanisms of food deterioration are microbial spoilage and oxidation. For protecting foods from these deteriorative changes, modified atmosphere packages or oxygen scavengers have been used applied with high gas-barrier packaging materials (Rooney, 1995; Vermeiren et ah, 1999). This technique of oxygen exclusion works against aerobic microbial growth and oxidative quality changes, but it cannot protect foods from spoilage and contamination due to the growth of facultative or obligate anaerobic bacteria. Heat processing of the packaged foods may also help preserve the food products from microbial deterioration. However, thermal processing is sometimes not useful to maintain specific food quality requirements, such as in the case of fresh or minimally processed foods. The concept of active packaging can contribute to the preservation of perishable foods that are sensitive to microbial spoilage or to oxidation (Miltz et al., 1995; Vermeiren et al, 1999). Antimicrobial packaging materials recently emerged as a potential means to assist in the preservation of perishable foods and extend their shelf life. Antioxidants may also be incorporated into packaging films, and will be released to protect the foods from oxidative degradation. T5^ically, in antimicrobial and antioxidant packaging systems the antimicrobial or antioxidant substances are incorporated into or coated onto their packaging materials, such as plastic films or papers (Vermeiren et aL, 1999; Appendini and Hotchkiss,
Innovations in Food Packaging ISBN: 0-12-311632-5
Copyright © 2005 Elsevier Ltd All rights of reproduction in any form reserved
Packaging containing natural antimicrobial or antioxidative agents 109
2002). Some specialized applications immobilize the agents to the polymers by ionic or covalent bonding. The active agents in the packaging material are designed to be released into the food or designed to function at the surface of the food product. The concept of controlled release of drugs has already been practiced widely in medical and pharmaceutical areas. However, the release of antimicrobial or antioxidant agents in active food packaging is relatively recent, and causes consumer concerns regarding their safety due to their possible migration into foods (Vermeiren et ah, 1999; Han, 2003). For this reason, there is a growing consumer preference for natural agents which have been isolated from microbiological, plant, and animal sources (Nicholson, 1998). Active substances of biological origin have a powerful wide-spectrum activity with low toxicity, and are expected to be used for food preservation as a means of active packaging (Han, 2003). Table 7.1 lists the natural preservatives and antioxidants to be considered for inclusion or adsorption into food packaging materials. For antimicrobial and antioxidative packaging applications, the agents should be incorporated into or coated on the packaging layer, remain stable there for a required time, and finally be released from the packaging surface in a controlled manner. Because most active compounds from biological origins are sensitive to heat, the thermal fabrication of plastics (such as extrusion and injection) offers limited possibilities for the inclusion of these substances directly in the polymer matrix without loss of their activity. Therefore, solvent compounding and solution coating are preferred, and will prevent the loss of these compounds' activity. When selecting the proper solvents and casting conditions, it is important to consider the solubility of the polymers and of the additives. Biopolymers such as proteins and carbohydrates are soluble in water, ethanol, and many other solvents, and thus are good for casting by solvent compounding (Appendini and Hotchkiss, 2002). However, these biopolymer films have limited stability to high humidity conditions, which restricts the range of applications. On the other hand, some agents such as plant extracts and bacteriocins are relatively heat-stable, and can be extruded or pressed with the use of mild heat. In this case, however, some activity loss may occur, and should be accounted for.
Table 7.1
Natural presen^itives I n d ahlic>xidaift5#r^^i^^
Type
Agents
Antimicrobials
Plant extracts from grapefruit seed, wasabi (allyl isothiocyanate), hinoki cypress (hinokitiol), bamboo, Rheum palmatum and Coptis chinesis Polypeptides such as nisin and pediocin Chitosan Enzymes such as lysozyme, glucose oxidase Monophenols and phenolic acids (a-tocopheroi) Organic acids (ascorbic acid) Plant extracts (rosemary, sage) Maillard reaction products
Antioxidant
From Rooney (1995); Ooki (1996); Han (2000).
1 1 0 Innovations in Food Packaging
Antimicrobial packaging Among the various natural antimicrobial agents, nisin, a polypeptide produced by Lactococcus lactis, has been most widely studied for its incorporation into packaging films. Because it is produced by a safe food-grade bacteria, has been consumed by humans for a long period of time without any recognized problems, and can be degraded in the human gastrointestinal tract by proteolytic enzymes, it is ideal for use as a biopreservative in foods. Nisin, a hydrophobic protein, has been granted GRAS (generally recognized as safe) status for its use in cheese products in the USA, and is effective against a wide range of spoilage and hazardous gram-positive bacteria (Hurst, 1983). Many recent studies have reported that nisin-incorporated packaging materials inhibit the growth of gram-positive bacteria, such as Brochothrix thermosphacta, Lactobacillus helveticus, Listeria monocytogenes, Micrococcus flavus, and Pediococcus pentosaceus (Daeschel et al, 1992; An et al., 2000), and have also extended the shelf life of perishable foods by suppressing the growth of spoilage bacteria (Siragusa et ai, 1999; Kim et ai, 2002a). Nisin can withstand moderate thermal processing and exposure to acidic environments without major activity loss (Ray, 1992), which confers high merit for the incorporation in food packaging materials. It is stable in a dry form for years, and thus is expected to be safe when incorporated into the polymer structure (Riick and Jager, 1995; An et aL, 2000). Daeschel et al. (1992) treated silicon surfaces to absorb nisin so as to retain its antimicrobial activity. L. monocytogenes cells exposed to the surfaces failed to grow, and lost their metabolic activity (Bower et al., 1995). Higher amounts of nisin were absorbed onto surfaces with high hydrophobicity, but such nisin possessed less antimicrobial activity than that which was absorbed onto surfaces of lower hydrophobicity. Scannell et al. (2000) fabricated cellulose-based packaging inserts absorbed with nisin, which retained its antimicrobial activity and was effective against L. lactis. Listeria innocua and Staphylococcus aureus. Cutter and Siragusa (1997) immobilized nisin onto edible alginate gels to be ground with beef tissue. Extrusion of low-density polyethylene (LDPE) containing nisin, at moderately low temperatures of 120°C, has been reported to retain the antimicrobial activity of nisin in its plastic structure (Siragusa et al., 1999). The nisin-fiUed film was seen to inhibit bacterial growth on meat surfaces. However, extrusion or heat-setting at high processing temperatures, above 140°C, resulted in a complete loss of nisin's activity due to its denaturation (Hoffman etal., 1998). Owing to the possible antimicrobial activity loss during thermal processes, solution coating or solvent casting processes have attempted to incorporate nisin into the packaging matrix. When a preservative is incorporated into or added as a surface layer onto the film structure by coating or solvent casting processes, the total amount of active substance and the corresponding material costs can be reduced. On the other hand, when a preservative is incorporated into the whole film structure by extrusion, a larger amount of the preservative is needed to mix with the entire resin. An LDPE film coated with nisin and a polyamide binder have also suppressed the microbial growth of M. flavus andZ. monocytogenes in phosphate buffer solutions when in contact with
Packaging containing natural antimicrobial or antioxidative agents 111
the film (An et al., 2000). The plastic films with nisin inhibited the microbial growth of total aerobic and coliform bacteria on shelled oysters and on ground beef at 3° and 10°C, as well as extending the products' shelf life significantly (Kim et aL, 2002a). Therefore, it has been proposed that solution coating on the food contact surface can provide more effective antimicrobial activity (An et al, 2000; Kim et aL, 2002a). A thinner coating with higher concentrations of nisin possessed higher antimicrobial activity compared to a thicker coating with lower concentrations of nisin (An et al., 2000). When nisin (0.1% concentration) was incorporated into LDPE by extrusion, it did not migrate into distilled water at room temperature, however, it migrated into saline water that contained a surfactant (Siragusa et aL, 1999; Table 7.2). A heating treatment (at boiling temperature) or a mild surfactant treatment caused the migration of nisin from the LDPE film. It was thus suggested that nisin was not chemically bound to the LDPE structure (Siragusa et al, 1999). Kim et ai (2000) also showed that the presence of salt in food simulants increased the equilibrated migration level of nisin from a polyamide coating layer. However, the incorporation of sodium chloride, citric acid, and a surfactant into the coating medium did not enhance nisin's migration, nor the film's antimicrobial activity (Kim et a/., 2000). It was therefore suggested by ChiZhang et al. (2004) that controlled releasing nisin-incorporated packaging materials could be combined with direct nisin addition into foods for more effective antimicrobial activity against L. monocytogenes. The type of polymer affects the migration rate and the equilibrium concentration. Kim et al. (2002b) reported that a vinyl acetate-ethylene copolymer coating on paperboard caused a higher migration level of nisin compared to an acrylic polymer. The diffusion coefficients of nisin in an acrylic polymer and in a vinyl acetate-ethylene copolymer coating at 10°C were in the range of 1.1 X 10~^^ to 4.2 X 10"^^m^s"\ and 6.8 X 10"^^ to 12.2 X 10~^^m^s~\ respectively. The migration of nisin from polyvinyl alcohol (PVOH) at ambient temperature has a diffusion coefficient ranging from3.01 X 10"^"^ to 8.61 X 10"^^ m2s"\ with a partition coefficient of 26-153 as a concentration ratio in the polymer to the simulant (Buonocore et al, 2003). The diffusion coefficient in a swollen polymer matrix decreased with increasing cross-linking
Table 7.2
Activity of migrated nisin from nisin-impregnated LDPE film
Extraction conditions
Film with 0 . 1 % Film with 0 . 1 % active nisin active nisin (7 min. extrusion) (14 min. extrusion)
Water for 315 min. at room temperature Boiling water (100°C) for 5 min. + Boiling in 0.02N HCI solution for 5 min. + Saline water + 0.5% Tween 20 + at room temperature Saline water + 0.5%Tween 20 + at boiling for 5 min. From Siragusa etal. (1999), reproduced with permission.
Film with 0.05% active nisin (7 min. extrusion)
+ + +
+ + +
+
+
Innovations in Food Packaging
ratio and partition coefficient. Higher partitioning of nisin in the polymer provides a great benefit to slow-release mechanics (Han, 2003). Cast films of biopolymers demonstrated higher migration profiles of nisin activity compared to the heat-pressed films (Cha et al, 2003). Although changing the coating materials resulted in significant differences in the suppression of microbial growth in water and in microbial mediums, no antimicrobial activity difference was found in coating materials used in real foods, such as pasteurized milk and orange juice (Kim et aL, 2002b; Figure 7.1). The suppression of the microbial growth in real foods does not exhibit the same results as those in food simulants and in microbial mediums (Appendini and Hotchkiss, 2002). Other bacteriocins, such as pediocin and lacticin, have also been incorporated into packagingfilmsto create antimicrobial packaging systems (Ming et ai, 1997; Scannell et ai, 2000). Nisin and other bacteriocins can inhibit gram-positive bacteria; however, they are ineffective against molds, yeasts and gram-negative bacteria, with the exclusion of a few strains (Hurst, 1983). There have been some approaches to improving 10 8^
Aerobic bacteria in milk contacting 3% H nisin-incorporated coatings
Micrococcus flavus in nutrient broth contacting 5% nisin-incorporated coatings
J
d
-]
E
A
4H
/ •
4
250 200 H
^
'
10
6
Time (days)
Time (days)
^
A /
14
Nisin migrated from 5% nisin-incorporated coatings
12
Yeasts in orange juice contacting 3% nisin-incorporated coatings
10
c o
150
8
A
6
100
4
50 2
0-: Time (days)
.—^'^c 4
6
8
10
12
Time (days)
Migration and microbial growth profiles in food simulant or microbial medium contacting nisin-coated paper at 10°C. O, acrylic polymer coating only; D , vinyl acetate-ethylene copolymer coating only; • , acrylic polymer with nisin; • , vinyl acetate-ethylene copolymer with nisin. From Kim eta\. (2002b), reprinted with permission o fJohn Wiley & Sons Ltd.
Packaging containing natural antimicrobial or antioxidative agents 113
the effectiveness of bacteriocin-incorporated packaging materials by incorporating chelating agents such as EDTA (Nicholson, 1998). A higher hydrophobicity at an acidic pH was reported to exert higher inhibitory activity of nisin against L. monocytogenes in the ediblefilmsincluding whey protein, soy protein, egg albumin, and wheat gluten (Ko era/., 2001). Appendini and Hotchkiss (1997) have immobilized the antimicrobial agent, lysozyme, in PVOH, nylon and cellulose triacetate (CTA) films. CTA films incorporated with lysozyme demonstrated the highest antimicrobial activity against Micrococcus lysodeikticus. Higher antimicrobial activities were obtained when larger amounts of lysozyme were incorporated, up to 150-200 mg enzyme/g polymer, while the film thickness did not affect the activity significantly. The antimicrobial activity of lysozyme may be reduced due to its conformational changes when lysozyme is adsorbed onto a solid surface (Bower et a/., 1998). Release of lysozyme in PVOH film at ambient temperatures had a diffusion coeflficient of 3.83 X 10"^^ to 9.98 X 10"^^m^s"^ with a partition coefficient of 6 to 432 (Buonocore, 2003). Increasing the cross-linking degree decreased the diffusion coefficient and increased the partition coefficient of lysozyme. Glucose oxidase may be immobilized in a polymer matrix to confer antimicrobial activity, due to a catalysis reaction yielding hydrogen peroxide from glucose and oxygen (Appendini and Hotchkiss, 2002). Chitosan is a biopolymer with good antimicrobial abilities, because it inhibits the growth of a wide variety of fungi, yeasts and bacteria. In addition, it forms a film almost by itself after it has been dissolved in acid solution (Begin and Van Calsteren, 1999). It is a cationic polysaccharide of (3-1,4 linkages obtained by the deacetylation of chitin, which is collected from cructaceans or various fungi. Commercial chitosan products usually have a molecular weight ranging from 100 000 to 1200 000 daltons, but oligomer products with lower molecular weight can be produced by thermal, enzymatic, and/or chemical degradation (Li et al., 1997). Chitosan is readily soluble in various acidic solvents, and has high antimicrobial activity against many pathogenic and spoilage micro-organisms (Tokura et al., 1997; Tsai et al, 2002). However, the antimicrobial activity of chitosan depends on its molecular weight, and the degree of deacetylation and of chemical degradation. Tokura et al (1997) observed growth inhibition of Escherichia coli by chitosan of molecular weight 9300g/mole, but not by that of molecular weight 2200 g/mole. Tsai et al (2002) reported that the antimicrobial activity of chitosan increased with the degree of deacetylation. Both grampositive and gram-negative bacteria were inhibited by antimicrobial LDPE films incorporated with chitosan above 1.43% in LDPE (Park et a/., 2002). Chitosan incorporated in LDPE could be released into the culture broth. Chito-oligosaccharide was immobilized on PVOH by chemical cross-linking, and exhibited reduction in S. aureus bacterial counts in culture medium (Cho et al, 2000). Chitosanfilmscan also be used as a delivery system for organic acids to exhibit antimicrobial functions (Ouattarae^a/., 2000). Different plant extracts have been used for antimicrobial packaging purposes. Extracts of grapefruit seed. Rheum palmatum and Coptis chinesis have been included into LDPE films by extrusion (Chung et al, 1998; Lee et al, 1998; Ha et al, 2001). Grapefruit seed extracts in a solution form in glycerol, and in a powder form, have
114
Innovations in Food Packaging
been added in master-batch compounding for film fabrication. Other alcohoHc or aqueous plant extracts have been dried by freeze drying or spray drying, and have been blended with polymer pellets to produce films (Chung et al., 1998). The extracts retained partial antimicrobial activity after the thermal extrusion process. Grapefiiiit seed extract exhibits a wide spectrum of microbial growth inhibition, and has been reported to contain naringin, ascorbic acid, hesperidin, and various organic acids such as citric acid. In addition, in some countries it is permitted for use as a food additive (Sakamoto et ai, 1996; Lee et ai, 1998). Its water-solublefi*actionhas antimicrobial activity and contains three reactive components identified by gas chromatography (Cho et al, 1994). Sakamoto et al. (1996) identified triclosan and methyl-p-hydroxybenzote to be the active antimicrobial components in grapefinit seed extract. Kim et al. (1994) reported the existence of antimicrobial chitinase in the extract, which is stable to heat treatments. The antimicrobial activity of grapefruit seed extract was stable at high temperatures of up to 120°C (Kim and Cho, 1996), and was retained after film fabrication processes (Lee et al, 1998). Films containing grapefruit seed extracts were effective in inhibiting the growth of aerobic bacteria and/or coliforms onfi*eshproduce and on ground beef, when contact packaging was used (Chung et al., 1998; Lee et al, 1998; Ha et al, 2001). Another plant extract used for commercial antimicrobial packaging is wasabi extract, or Japanese horseradish (Koichiro, 1993). The main active antimicrobial ingredient in wasabi extract is known to be the volatile allyl isothiocyanate (AIT). The AIT gas inhibits many fiingi and bacteria. The minimal inhibition concentration of AIT against Yersinia enterocolitica and L. monocytogenes is in the range of 14-145 ppm at 10^0°C (Kusunoki et al, 1998). The extract has been encapsulated in cyclodextrin to control the volatility of AIT (Figure 7.2). The AIT in the encapsulated powder (dry form) is suggested not to be volatile, but becomes volatile when the AIT-cyclodextrin
100 Relative humidity (%) Figure 7.2 Volatility o f allyl isothiocyanate encapsulated in different matrixes. • , zeolite; • , cyclodextrin. From Koichiro (1993).
Packaging containing natural antimicrobial or antioxidative agents 1 1 5
complex is exposed to high humidity conditions after the packaging of the food product (Koichiro, 1993). The evaporated AIT then migrates to the food surface, and inhibits the growth of aerobic bacteria such as Aspergillus niger, Penicillium italicum, S. aureus, and E. coli. Stronger antimicrobial activity of AIT was reported at higher RH, suggesting that moisture has a significant fimction in AIT's antimicrobial ability (Furuya and Isshiki, 2001). The AIT-cyclodextrin complex powder has been incorporated in packaging materials of drip sheets, polyethylene films, and tablets. These products are commercially available in Japan, and are used for rice lunch boxes, meats, andfireshproduce. A design of the drip sheet is shown in Figure 7.3. Volatile components from essential oils of mustard, cinnamon, garlic and clove have been added tofilterpapers to inhibit spoilagefimgiin breads, such as Aspergillus flavus, Endomyces fibuliger, and Penicillium commune (Nielsen and Rios, 2000). Nielsen and Rios (2000) have suggested using AIT from mustard as the active component in the packaging of bread. Packaging materials incorporating a single biopreservative have limitations in ensuring the safety and extending the shelf life of foods, because they can only inhibit specific microbes. For example, nisin-incorporated packaging materials suppress the growth of gram-positive bacteria effectively (Daeschel et ah, 1992; Bower et al., 1995; Siragusa et al., 1999; An et al., 2000), but it does not work against gram-negative bacteria such as E. coli (Cha et aL, 2002). However, a narrow antimicrobial spectrum may, in certain cases, be desirable for packaged foods in which microbial contamination is caused by only a specific type of strain. Nonetheless, generally packaging materials with a wide antimicrobial spectrum are more desirable for universal use and to improve the storage stability of a variety of food products. In an effort to achieve this, Cha et al. (2002) incorporated several antimicrobial agents into films made of Na-alginate and K-carrageenan. The addition of EDTA and grapefruit seed extract to bothfilmsgave a strong inhibition against Micrococcus luteus, L. innocua, Salmonella enteritidis, E. coli, and S. aureus; however, Na-alginate based films with the addition of nisin, lysozyme, and EDTA showed the strongest inhibition against the same bacterial strains. Table 7.3 shows their Na-alginate based film results. In a similar approach, Lee et al. (2003) fabricated a paperboard coated with nisin and chitosan combinations which had been dissolved in a vinyl acetate-ethylene copolymer. Perforated polypropylene film Cyclodextrin layer with wasabi extract
Non-woven fiber layer
Figure 7.3
Design o f drip siieet incorporating wasabi extract. From Koichiro (1993).
116 Innovations in Food Packaging
Table Z 3
^f^setsiio^w^
in JMa-adginatefilmsjon several organisms
Film
Strain Micrococcus luteus Listeria innocua Salmonella enteritidis Escherichia coliStaphylococcus aureus ATCC 25923 ATCC10240 ATCC 33090 ATCC14931 ATCC 9637
Control without antimicrobial additive With nisin With lysozyme With nisin + EDTA With lysozyme + EDTA With nisin + lysozyme + EDTA With EDTA With EDTA + grapefruit seed extract With grapefruit seed extract
++ + ++ + + + ++++ ++ + ++ +
+++
+++
++ +
-++
++
+
+ +
-+
+ -1-
-, no inhibition; + , weak inhibition ( < 2 mm in inhibition zone); + + , inhibition zone o f 2-5 mm; + + + , strong inhibition with diameter > 5 mm. From Cha etal. (2002), reproduced with permission.
Nisin and chitosan migrated into water and equilibrated at about 8% for nisin and 1% for chitosan. In addition, the release rates and levels were not affected by the presence of other preservatives in the polymer coating. Nisin and chitosan in an acidified vinyl acetate-ethylene copolymer coating layer exhibited strong microbial inhibition against L monocytogenes and E. coli 0157:H7, and improved the microbial quality of milk and orange juice stored at 10°C. Cha et al. (2003) also designed chitosan films containing nisin with a strong antimicrobial activity against M luteus. Antimicrobial packaging systems containing natural antimicrobial agents can confer specific or broad microbial inhibition, depending on the agents used and their concentrations. Different types of antimicrobial-delivery mechanisms, polymers, and packaging material - food combinations may be appHed or used to maximize the effectiveness of the system.
%rTi:!OYidative p a c k a g i n g Antioxidants can be incorporated into or coated onto food packaging materials to control the oxidation of fatty components and pigments, and thus can contribute to the quality preservation of foods (Vermeiren et al, 1999). The antioxidants incorporated into plastic packaging materials may have the dual role of protecting the polymer as well as the packaged food from oxidation (Waite, 2003). Antioxidative packaging can retard the oxidative reactions of fatty ingredients in packaged foods. The incorporation of synthetic antioxidants, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), in high-density polyethylene (HDPE) liners have been shown to protect cereals from oxidation (Miltz et a/., 1988; Wessling et al, 2001). However, because of the growing concern about the use of food chemicals, there is greater interest in using
Packaging containing natural antimicrobial or antioxidative agents 117
CD O
c CO
o
CO
c o CO
•D
Time (days) Figure 7.4 Effect o f a-tocopherol-incorporated LDPE film on the oxidation o f linoleic emulsion at 6°C. • , no addition; A , added in 360 ppm; # , added in 3400 ppm. From Wessling etal. (2000), reprinted with permission o fJohn Wiley & Sons Ltd.
natural antioxidants such as a-tocopherol and ascorbic acid. In particular, a-tocopherol can be easily dissolved into polyolefins and does not break down under pol3aner processing conditions. A significant concentration of a-tocopherol also usually remains in the final plastic films (Ho et aL, 1998; Wessling et al, 1999). Zambetti et al (1995) found that the use of a-tocopherol as an antioxidant in LDPE used in extrusion coating, and in HDPE used in extrusion-blown bottles, improved the sensory performance of the bottled water by preventing the oxidation of the polymer substrates. Wessling et al. (1999) found that a-tocopherol incorporated into polypropylene (PP) retained more of its activity than when incorporated into LDPE, when bothfilmswere in contact with various foods and food-simulating liquids. The a-tocopherol in LDPE decreased at considerably higher rates with high fat-containing foods or with high-alcohol liquids. Therefore, LDPE containing an active antioxidant can offer the potential of being used as an active packaging because it can help to transfer the incorporated a-tocopherol onto the packaged foods, which will help prevent the oxidation of the food products. PP may be used as oxygen-scavenging packaging in the headspace or at the packaged foods' surface. LDPEfilmsthat incorporated a-tocopherol above 360 ppm delayed the oxidation of linoleic acid emulsions at 6°C (Figure 7.4), but did not do so at 20° and 40°C (Wessling et al, 2000). LDPE films containing a-tocopherol above 700 ppm could not prevent the oxidation of oatmeal at 20°C; this is probably due to the poor contact of the packagingfihnwith the oatmeal product (Wessling et al, 2001). For a-tocopherol-incorporated films to be effective, it is necessary that there is close contact between the packaging material and the food product. The a-tocopherol in the film is degraded chemically without volatiles being loss, while BHT diffuses out of thefilmand is volatilized on the surface, eventually migrating to the dry food (Miltz et al, 1988; Wessling et al, 2001). Another concern with a-tocopherol being incorporated into LDPE films is the potential changes it causes in the mechanical properties, color, and oxygen permeability of the film (Wessling et al, 2000).
Innovations in Food Packaging
Ascorbic acid can scavenge oxygen in the headspace air of canned or bottled products. Its ability to scavenge oxygen has made it a possible candidate for scavenging oxygen in active food packaging technologies (Smith et ah, 1995). Ascorbic acid in combination with other antioxidants can act as an antioxidant, and can retard rancidity (Yanishlieva-Maslarova, 2001). It can also protect against the peroxidation of lipid components by trapping the peroxyl radical in the aqueous phase. Due to this, the antioxidative property of ascorbic acid has been incorporated into and used in the fabrication of oxygen-scavenging plastics (Rooney, 1995). Perishable foods that are sensitive to both microbial spoilage and oxidative deterioration may be packaged in polymeric materials containing both antimicrobial and antioxidant additives. Lee et al. (2004) produced antimicrobial and antioxidant packaging materials that incorporated nisin and/or a-tocopherol. They examined their effectiveness with an emulsion model system and in milk cream. At 10°C, a-tocopherol migrated into an oil-in-water emulsion at a faster rate and reached an equilibrium level at about 6%, while nisin migrated at about 9%. Therefore, the inclusion of both a-tocopherol and nisin in coated paper could provide antimicrobial and antioxidative functions. However, no synergic or interactive effects in the antimicrobial or antioxidative activities were observed by the use of the combination (Lee et al, 2004). One application combining ascorbic acid and silver zeolite has been reported for antioxidative and antimicrobial activity (Rooney, 1995).
Antimicrobial and antioxidative packaging systems containing natural active substances may have high potential for commercial food packaging applications. Consumers would prefer to obtain better food safety of fresh produce and minimally processed foods using this type of packaging system. However, it is necessary that new active packaging systems must satisfy food safety regulations, which are different in each country. Greater food safety and quality assurance may be improved by the use of both antimicrobial and antioxidative packaging systems incorporating natural active agents. Some commercial products, such as films coated with wasabi extract, are already on the market and satisfy the regulations and consumer needs of particular countries. Most materials containing natural active agents are more effective when there is direct contact of the packaging materials with the food product. For new packaging systems to be introduced into the market effectively, careful design is required. Natural antimicrobials and antioxidants are usually costly, and therefore further development of package design using the minimum of active agents is desirable for practical applications. Food contact layers with the appropriate concentrations of the active agents may be laminated or coated onto the barrier layer of the package structure. There are some suggestions that before long many countries would adopt the new active packaging concepts into their packaging regulations. Therefore, new applications of antimicrobial and antioxidative packaging are likely to be available in the market sooner or later.
Packaging containing natural antimicrobial or antioxidative agents 1 1 9
References
An, D. S., Kim, Y. M., Lee, S. B., Paik, H. D. and Lee, D. S. (2000). Antimicrobial low density polyethylene film coated with bacteriocins in binder medium. Food Sci. Biotechnol 9,14-20. Appendini, P. and Hotchkiss, J. H. (1997). Immobilization of lysozyme on food contact polymers as potential antimicrobial films. Packag. Technol Sci. 10, 271-279. Appendini, P. and Hotchkiss, J. H. (2002). Review of antimicrobial food packaging. Innov. Food Set Emerg. Technol. 3,113-126. Begin, A. and Van Calsteren, M. (1999). Antimicrobial films produced from chitosan. Intl J. Biol. Macromol. 26, 63-67. Bower, C. K., McGure, J. and Daeschel, M. A. (1995). Protein antimicrobial barriers to bacterial adhesion. Appl. Environ. Microbiol. 61, 992-997. Bower, C. K., Daeschel, M. A. and McGuire, J. (1998). Suppression of Listeria monocytogenes colonization following adsorption of nisin onto silica surfaces. J. Dairy Sci. 81,2771-2778. Buonocore, G. G., Del Nobile, M. A., Panizza, A., Corbo, M. R. and Nicolais, L. (2003). A general approach to describe the antimicrobial agent release from highly swellable films intended for food packaging applications. J. Contr. Release 90, 97-107. Cha, D. S., Choi, J. H., Chinnan, M. S. and Park, H. J. (2002). Antimicrobial films based on Na-alginate and K-carrageenan. Lebensm. Wiss. u. Technol. 35, 715-719. Cha, D. S., Cooksey, K., Chinnan, M. S. and Park, H. J. (2003). Release of nisin from various heat-pressed and cast films. Lebensm. Wiss. u. Technol. 36, 209-213. Chi-Zhang, Y, Yam, K. L. and Chikindas, M. L. (2004). Effective control of Listeria monocytogenes by combination of nisin formulated and slowly released into a broth system. IntlJ. Food Microbiol. 90, 15-22. Cho, S. H., Chung, J. H. and Ryu, C. H. (1994). Inhibitory effects of natural antimicrobial agent on postharvest decay in fruits and vegetables under natural low temperatures. J. Korean Soc. Food Nutr 23, 315-321. Cho, Y W., Han, S. S. and Ko, S. W. (2000). PVA containing chito-oHgosaccharide side chain. Polymer 41, 2033-2039. Chung, S. K., Cho, S. H. and Lee, D. S. (1998). Modified atmosphere packaging of fresh strawberries by antimicrobial plastic films. Korean J. Food Sci. Technol. 30,1140-1145. Cutter, C. N. and Siragusa, G. R. (1997). Growth of Brochothrix thermosphacta in ground beef following treatments with nisin in calcium alginate gels. Food Microbiol. 14, 425^30. Daeschel, M. A., Mcguir, J. and Al-Makhalafi, H. (1992). Antimicrobial activity of nisin adsorbed to hydrophilic and hydrophobic and hydrophobic silicon surfaces. J. Food Prot. 55,731-755. Furuya, K. and Isshiki, K. (2001). Effect of humidity on allyl isothiocyanate antimicrobial activity. J. Japanese Soc. Food Sci. Technol. (in Japanese) 48, 738-743. Ha, J. U., Kim, Y M. and Lee, D. S. (2001). Multilayered antimicrobial polyethylene films applied to the packaging of ground beef Packag. Technol. Sci. 14, 55-62. Han, J. H. (2000). Antimicrobial food packaging. Food Technol. 54(3), 56-65. Han, J. H. (2003). Antimicrobial food packaging. In: Novel Food Packaging Technologies (R. Ahvenainen, ed.), pp. 50-70. Woodhead Publishing, Cambridge, UK.
120 Innovations in Food Packaging
Ho, Y. C , Young, S. S. and Yam, K. L. (1998). Vitamin E based stabilizer components in HDPE polymer. I Vinyl Add. Technol 4,139-150. Hoffinan, K. L., Dawson, P. L., Acton, J. C , Han, I. Y and Ogale, A. A. (1998). Film formation effects on nisin activity in com zein and polyethylene films. Activities Report R & D Associates 50(1), 238-244. Hurst, A. (1983). Nisin and other inhibitory substances from lactic acid bacteria. In: Antimicrobials in Foods (A. L. Branen and P. M. Davidson, eds), pp. 327-351. Marcel Dekker, New York, NY Kim, Y R. and Cho, S. H. (1996). Antimicrobial activities and effect of grapefruit seed extract on the physiological function of microorganisms. Korean J. Post-Harvest Sci. Technol. Agric. Prod. 3,187-193. Kim, W. Y, Cheong, N. E., Jae, D. Y et al. (1994). Characterization of an antimicrobial chitinase purified from the grapefruit seed extract. Korean J. Plant Pathol. 10,277-283. Kim, Y M., Lee, N. K., Paik, H. D. and Lee, D. S. (2000). Migration of bacteriocin from bacteriocin-coated film and its antimicrobial activity. Food Sci. Biotechnol. 9, 325-329. Kim, Y M., Paik, H. D. and Lee, D. S. (2002a). Shelf life characteristics of fresh oysters and ground beef as affected by bacteriocin-coated plastic packaging film. J. Sci. Food ^gr/c. 82, 998-1002. Kim, Y M., An, D. S., Park, H. J., Park, J. M. and Lee, D. S. (2002b). Properties of nisinincorporated polymer coating as antimicrobial packaging materials. Packag. Technol. Sci. 15,247-254. Ko, S., Janes, M. E., Hettiarachchy, N. S. and Johnson, M. G. (2001). Physical and chemical properties of edible films containing nisin and their action against Listeria monocytogenes. J. Food Sci. 66, 1006-1011. Koichiro, Y (1993). Keeping freshness by antimicrobial packaging incorporating wasabi extract. Food Sci. (in Japanese) 35(11), 102-107. Kusunoki, H., Shin, K., Kokubo, Y, Kaneko, S., Sekiyama, Y and Uemura, T. (1998). Antimicrobial activity of allyl isothiocyanate against low temperature growth bacteria. Japan. J. Food Microbiol, (in Japanese) 15, 107-112. Lee, D. S., Hwang, Y L and Cho, S. H. (1998). Developing antimicrobial packaging film for curled lettuce and soybean sprouts. Food Sci. Biotechnol. 7,117-121. Lee, C. H., An, D. S., Park, H. J. and Lee, D. S. (2003). Wide-spectrum antimicrobial packaging materials incorporating nisin and chitosan in the coating. Packag. Technol. Sci. 16, 99-106. Lee, C. H., An, D. S., Lee, S. C , Park, H. J. and Lee, D. S. (2004). A coating for use as an antimicrobial and antioxidative packaging material incorporating nisin and a-tocopherol. J. FoodEng. 62,323-329. Li, Q., Dunn, E. T., Gransmaison, E. W. and Goosen, M. E A. (1997). Applications and properties of chitosan. In: Applications of Chitin and Chitosan (M. F. A. Goosen, ed.), pp. 1-29. Technomic Publishing, Lancaster, PA. Miltz, J., Passy, N. and Manneheim, C.H. (1995). Trends and applications of active packaging systems. In: Foods and Packaging Materials - Chemical Interactions (P. Ackermann, M. Jagerstad andT. Ohlsson, eds), pp. 201-210. The Royal Society of Chemistry, Cambridge, UK.
Packaging containing natural antimicrobial or antioxidative agents 121
Miltz, J., Hoojjat, P., Han, J. K., Giacin, J. R., Harte, B. R. and Gray, I. J. (1988). Loss of antioxidants from high-density polyethylene: its effect on oatmeal cereal oxidation. In: Food and Packaging Interactions (J. H. Hotchkiss, ed.), pp. 83-93. American Chemical Society, Washington DC, USA. Ming, X., Weber, G. H., Ayres, J. W. and Sandine, W. E. (1997). Bacteriocins applied to food packaging materials to inhibit Listeria monocytogenes on meats. J. Food Sci. 62,413-415. Nicholson, M. D. (1998). The role of natural antimicrobials in food/packaging biopreservation. J. Plast. Film Sheet 14, 235-241. Nielsen, R V and Rios, R. (2000). Inhibition of fringal growth on bread by volatile components from spices and herbs, and the possible application in active packaging, with special emphasis on mustard essential oil. IntlJ. Food Microbiol 60, 219-229. Ooki, K. (1996). Antimicrobial films for food packaging. Japan. Food Sci. (in Japanese) 35(10), 57-67. Ouattara, B., Simard, R. E., Piette, G., Begin, A. and Holley, R. A. (2000). Diffiision of acetic acid and propionic acid from chitosan based antimicrobial packaging films. J. Food Sci. 65,16^-113. Park, S. I., Marsh, K. S., Dawson, R L., Acton, J. C. and Han, I. (2002). Antimicrobial activity of chitosan incorporated polyethylene films. Paper No. lOOB-23, 2002 IFT Annual Meeting Book of Abstracts, p. 250. Institute of Food Technologists, Anaheim, CA. Ray, B. (1992). Nisin of Lactococcus lactis ssp. lactis as a food biopreservative. In: Food Biopreservatives of Microbial Origin (B. Ray and M. Daeschel, eds), pp. 207-264. CRC Press, Boca Raton, FL. Rooney, M. L. (1995). Active packaging in polymer films. In: Active Food Packaging (M. L. Rooney, ed.), pp. 74-110. Blackie Academic & Professional, Glasgow, UK. Riick, E. and Jager, M. (1995). Antimicrobial Food Additives, 2nd edn., pp. 208-213. Springer, Berlin, Germany. Sakamoto, S., Sato, K., Maitani, T. and Yamada, T. (1996). Analysis of components in natural food additive 'grapefinit seed extract' by HPLC and LC/MS. Bull. Natl (Japan) Inst. Health Sci. 114, 38-42. Scannell, A. G. M., Hill, C , Ross, R. R, Marx, S., Hartmeier, W. and Arendt, E. K. (2000). Development of bioactive food packaging materials using immobilised bacteriocins Lacticin 3147 andNisaplin. Ml J Food Microbiol. 60, 241-249. Siragusa, G. R., Cutter, C. N. and Willett, J. L. (1999). Incorporation of bacteriocin in plastic retains activity and inhibits surface growth of bacteria on meat. Food Microbiol. 16,229-235. Smith, J. P., Hoshino, J. and Abe, Y. (1995). Interactive packaging involving sachet technology. In: Active Food Packaging (M. L. Rooney, ed.), pp. 143-173. Blackie Academic & Professional, Glasgow, UK. Tokura, S., Ueno, K., Miyazaki, S. and Nishi, N. (1997). Molecular weight dependent antimicrobial activity by chitosan. Macromol. Symp. 120, 1-9. Tsai, G. J., Su, W. H., Chen, H. C. and Pan, C. L. (2002). Antimicrobial activity of shrimp chitin and chitosan from different treatments and applications of fish preservation. Fisheries Sci. 68, 170-177.
1 2 2 Innovations in Food Packaging
Vermeiren, L., Devlieghere, R, Van Beest, M., de Kruijf, N. and Debevere, J. (1999). Developments in the active packaging of foods. Trends FoodSci. Technol. 10,77-86. Waite, N. (2003). Active Packaging, pp. 75-84. Pira International, Leatherhead, UK. Wessling, C , Nielsen, T., Leufven, A. and Jagerstad, M. (1999). Retention of a-tocopherol in low-density polyethylene (LDPE) and polypropylene (PP) in contact with foodstuffs and food-simulating liquids. J. Sci. FoodAgric. 79, 1635-1641. Wessling, C, Nielsen, T. and Andres, L. (2000). The influence of a-tocopherol concentration on the stability of linoleic acid and the properties of low-density polyethylene. Packag. Technol. Sci. 13, 19-28. Wessling, C , Nielsen, T. and Giacin, J. R. (2001). Antioxidant ability of BHT- and a-tocopherol-impregnated LDPE film in packaging of oatmeal. J. Sci. Food Agric. SI, 194-201. Yanishlieva-Maslarova, N. V (2001). Inhibiting oxidation. In: Antioxidants in Food: Practical Applications (J. Pokomy, N. Yanishlieva and M. Gordon, eds), pp. 23-70. Woodhead Publishing, Cambridge, UK. Zambetti, P. R, Baker, S. L. and Kelley, D. C. (1995). Alpha tocopherol as an antioxidant for extrusion coating polymers. TappiJ. 78(4), 167-171.
introduction Antimicrobial packaging Antioxidative packaging Future potential References
108 110 116 118 119
Introduction The most frequent mechanisms of food deterioration are microbial spoilage and oxidation. For protecting foods from these deteriorative changes, modified atmosphere packages or oxygen scavengers have been used applied with high gas-barrier packaging materials (Rooney, 1995; Vermeiren et ah, 1999). This technique of oxygen exclusion works against aerobic microbial growth and oxidative quality changes, but it cannot protect foods from spoilage and contamination due to the growth of facultative or obligate anaerobic bacteria. Heat processing of the packaged foods may also help preserve the food products from microbial deterioration. However, thermal processing is sometimes not useful to maintain specific food quality requirements, such as in the case of fresh or minimally processed foods. The concept of active packaging can contribute to the preservation of perishable foods that are sensitive to microbial spoilage or to oxidation (Miltz et al., 1995; Vermeiren et al, 1999). Antimicrobial packaging materials recently emerged as a potential means to assist in the preservation of perishable foods and extend their shelf life. Antioxidants may also be incorporated into packaging films, and will be released to protect the foods from oxidative degradation. T5^ically, in antimicrobial and antioxidant packaging systems the antimicrobial or antioxidant substances are incorporated into or coated onto their packaging materials, such as plastic films or papers (Vermeiren et aL, 1999; Appendini and Hotchkiss,
Innovations in Food Packaging ISBN: 0-12-311632-5
Copyright © 2005 Elsevier Ltd All rights of reproduction in any form reserved
Packaging containing natural antimicrobial or antioxidative agents 109
2002). Some specialized applications immobilize the agents to the polymers by ionic or covalent bonding. The active agents in the packaging material are designed to be released into the food or designed to function at the surface of the food product. The concept of controlled release of drugs has already been practiced widely in medical and pharmaceutical areas. However, the release of antimicrobial or antioxidant agents in active food packaging is relatively recent, and causes consumer concerns regarding their safety due to their possible migration into foods (Vermeiren et ah, 1999; Han, 2003). For this reason, there is a growing consumer preference for natural agents which have been isolated from microbiological, plant, and animal sources (Nicholson, 1998). Active substances of biological origin have a powerful wide-spectrum activity with low toxicity, and are expected to be used for food preservation as a means of active packaging (Han, 2003). Table 7.1 lists the natural preservatives and antioxidants to be considered for inclusion or adsorption into food packaging materials. For antimicrobial and antioxidative packaging applications, the agents should be incorporated into or coated on the packaging layer, remain stable there for a required time, and finally be released from the packaging surface in a controlled manner. Because most active compounds from biological origins are sensitive to heat, the thermal fabrication of plastics (such as extrusion and injection) offers limited possibilities for the inclusion of these substances directly in the polymer matrix without loss of their activity. Therefore, solvent compounding and solution coating are preferred, and will prevent the loss of these compounds' activity. When selecting the proper solvents and casting conditions, it is important to consider the solubility of the polymers and of the additives. Biopolymers such as proteins and carbohydrates are soluble in water, ethanol, and many other solvents, and thus are good for casting by solvent compounding (Appendini and Hotchkiss, 2002). However, these biopolymer films have limited stability to high humidity conditions, which restricts the range of applications. On the other hand, some agents such as plant extracts and bacteriocins are relatively heat-stable, and can be extruded or pressed with the use of mild heat. In this case, however, some activity loss may occur, and should be accounted for.
Table 7.1
Natural presen^itives I n d ahlic>xidaift5#r^^i^^
Type
Agents
Antimicrobials
Plant extracts from grapefruit seed, wasabi (allyl isothiocyanate), hinoki cypress (hinokitiol), bamboo, Rheum palmatum and Coptis chinesis Polypeptides such as nisin and pediocin Chitosan Enzymes such as lysozyme, glucose oxidase Monophenols and phenolic acids (a-tocopheroi) Organic acids (ascorbic acid) Plant extracts (rosemary, sage) Maillard reaction products
Antioxidant
From Rooney (1995); Ooki (1996); Han (2000).
1 1 0 Innovations in Food Packaging
Antimicrobial packaging Among the various natural antimicrobial agents, nisin, a polypeptide produced by Lactococcus lactis, has been most widely studied for its incorporation into packaging films. Because it is produced by a safe food-grade bacteria, has been consumed by humans for a long period of time without any recognized problems, and can be degraded in the human gastrointestinal tract by proteolytic enzymes, it is ideal for use as a biopreservative in foods. Nisin, a hydrophobic protein, has been granted GRAS (generally recognized as safe) status for its use in cheese products in the USA, and is effective against a wide range of spoilage and hazardous gram-positive bacteria (Hurst, 1983). Many recent studies have reported that nisin-incorporated packaging materials inhibit the growth of gram-positive bacteria, such as Brochothrix thermosphacta, Lactobacillus helveticus, Listeria monocytogenes, Micrococcus flavus, and Pediococcus pentosaceus (Daeschel et al, 1992; An et al., 2000), and have also extended the shelf life of perishable foods by suppressing the growth of spoilage bacteria (Siragusa et ai, 1999; Kim et ai, 2002a). Nisin can withstand moderate thermal processing and exposure to acidic environments without major activity loss (Ray, 1992), which confers high merit for the incorporation in food packaging materials. It is stable in a dry form for years, and thus is expected to be safe when incorporated into the polymer structure (Riick and Jager, 1995; An et aL, 2000). Daeschel et al. (1992) treated silicon surfaces to absorb nisin so as to retain its antimicrobial activity. L. monocytogenes cells exposed to the surfaces failed to grow, and lost their metabolic activity (Bower et al., 1995). Higher amounts of nisin were absorbed onto surfaces with high hydrophobicity, but such nisin possessed less antimicrobial activity than that which was absorbed onto surfaces of lower hydrophobicity. Scannell et al. (2000) fabricated cellulose-based packaging inserts absorbed with nisin, which retained its antimicrobial activity and was effective against L. lactis. Listeria innocua and Staphylococcus aureus. Cutter and Siragusa (1997) immobilized nisin onto edible alginate gels to be ground with beef tissue. Extrusion of low-density polyethylene (LDPE) containing nisin, at moderately low temperatures of 120°C, has been reported to retain the antimicrobial activity of nisin in its plastic structure (Siragusa et al., 1999). The nisin-fiUed film was seen to inhibit bacterial growth on meat surfaces. However, extrusion or heat-setting at high processing temperatures, above 140°C, resulted in a complete loss of nisin's activity due to its denaturation (Hoffman etal., 1998). Owing to the possible antimicrobial activity loss during thermal processes, solution coating or solvent casting processes have attempted to incorporate nisin into the packaging matrix. When a preservative is incorporated into or added as a surface layer onto the film structure by coating or solvent casting processes, the total amount of active substance and the corresponding material costs can be reduced. On the other hand, when a preservative is incorporated into the whole film structure by extrusion, a larger amount of the preservative is needed to mix with the entire resin. An LDPE film coated with nisin and a polyamide binder have also suppressed the microbial growth of M. flavus andZ. monocytogenes in phosphate buffer solutions when in contact with
Packaging containing natural antimicrobial or antioxidative agents 111
the film (An et al., 2000). The plastic films with nisin inhibited the microbial growth of total aerobic and coliform bacteria on shelled oysters and on ground beef at 3° and 10°C, as well as extending the products' shelf life significantly (Kim et aL, 2002a). Therefore, it has been proposed that solution coating on the food contact surface can provide more effective antimicrobial activity (An et al, 2000; Kim et aL, 2002a). A thinner coating with higher concentrations of nisin possessed higher antimicrobial activity compared to a thicker coating with lower concentrations of nisin (An et al., 2000). When nisin (0.1% concentration) was incorporated into LDPE by extrusion, it did not migrate into distilled water at room temperature, however, it migrated into saline water that contained a surfactant (Siragusa et aL, 1999; Table 7.2). A heating treatment (at boiling temperature) or a mild surfactant treatment caused the migration of nisin from the LDPE film. It was thus suggested that nisin was not chemically bound to the LDPE structure (Siragusa et al, 1999). Kim et ai (2000) also showed that the presence of salt in food simulants increased the equilibrated migration level of nisin from a polyamide coating layer. However, the incorporation of sodium chloride, citric acid, and a surfactant into the coating medium did not enhance nisin's migration, nor the film's antimicrobial activity (Kim et a/., 2000). It was therefore suggested by ChiZhang et al. (2004) that controlled releasing nisin-incorporated packaging materials could be combined with direct nisin addition into foods for more effective antimicrobial activity against L. monocytogenes. The type of polymer affects the migration rate and the equilibrium concentration. Kim et al. (2002b) reported that a vinyl acetate-ethylene copolymer coating on paperboard caused a higher migration level of nisin compared to an acrylic polymer. The diffusion coefficients of nisin in an acrylic polymer and in a vinyl acetate-ethylene copolymer coating at 10°C were in the range of 1.1 X 10~^^ to 4.2 X 10"^^m^s"\ and 6.8 X 10"^^ to 12.2 X 10~^^m^s~\ respectively. The migration of nisin from polyvinyl alcohol (PVOH) at ambient temperature has a diffusion coefficient ranging from3.01 X 10"^"^ to 8.61 X 10"^^ m2s"\ with a partition coefficient of 26-153 as a concentration ratio in the polymer to the simulant (Buonocore et al, 2003). The diffusion coefficient in a swollen polymer matrix decreased with increasing cross-linking
Table 7.2
Activity of migrated nisin from nisin-impregnated LDPE film
Extraction conditions
Film with 0 . 1 % Film with 0 . 1 % active nisin active nisin (7 min. extrusion) (14 min. extrusion)
Water for 315 min. at room temperature Boiling water (100°C) for 5 min. + Boiling in 0.02N HCI solution for 5 min. + Saline water + 0.5% Tween 20 + at room temperature Saline water + 0.5%Tween 20 + at boiling for 5 min. From Siragusa etal. (1999), reproduced with permission.
Film with 0.05% active nisin (7 min. extrusion)
+ + +
+ + +
+
+
Innovations in Food Packaging
ratio and partition coefficient. Higher partitioning of nisin in the polymer provides a great benefit to slow-release mechanics (Han, 2003). Cast films of biopolymers demonstrated higher migration profiles of nisin activity compared to the heat-pressed films (Cha et al, 2003). Although changing the coating materials resulted in significant differences in the suppression of microbial growth in water and in microbial mediums, no antimicrobial activity difference was found in coating materials used in real foods, such as pasteurized milk and orange juice (Kim et aL, 2002b; Figure 7.1). The suppression of the microbial growth in real foods does not exhibit the same results as those in food simulants and in microbial mediums (Appendini and Hotchkiss, 2002). Other bacteriocins, such as pediocin and lacticin, have also been incorporated into packagingfilmsto create antimicrobial packaging systems (Ming et ai, 1997; Scannell et ai, 2000). Nisin and other bacteriocins can inhibit gram-positive bacteria; however, they are ineffective against molds, yeasts and gram-negative bacteria, with the exclusion of a few strains (Hurst, 1983). There have been some approaches to improving 10 8^
Aerobic bacteria in milk contacting 3% H nisin-incorporated coatings
Micrococcus flavus in nutrient broth contacting 5% nisin-incorporated coatings
J
d
-]
E
A
4H
/ •
4
250 200 H
^
'
10
6
Time (days)
Time (days)
^
A /
14
Nisin migrated from 5% nisin-incorporated coatings
12
Yeasts in orange juice contacting 3% nisin-incorporated coatings
10
c o
150
8
A
6
100
4
50 2
0-: Time (days)
.—^'^c 4
6
8
10
12
Time (days)
Migration and microbial growth profiles in food simulant or microbial medium contacting nisin-coated paper at 10°C. O, acrylic polymer coating only; D , vinyl acetate-ethylene copolymer coating only; • , acrylic polymer with nisin; • , vinyl acetate-ethylene copolymer with nisin. From Kim eta\. (2002b), reprinted with permission o fJohn Wiley & Sons Ltd.
Packaging containing natural antimicrobial or antioxidative agents 113
the effectiveness of bacteriocin-incorporated packaging materials by incorporating chelating agents such as EDTA (Nicholson, 1998). A higher hydrophobicity at an acidic pH was reported to exert higher inhibitory activity of nisin against L. monocytogenes in the ediblefilmsincluding whey protein, soy protein, egg albumin, and wheat gluten (Ko era/., 2001). Appendini and Hotchkiss (1997) have immobilized the antimicrobial agent, lysozyme, in PVOH, nylon and cellulose triacetate (CTA) films. CTA films incorporated with lysozyme demonstrated the highest antimicrobial activity against Micrococcus lysodeikticus. Higher antimicrobial activities were obtained when larger amounts of lysozyme were incorporated, up to 150-200 mg enzyme/g polymer, while the film thickness did not affect the activity significantly. The antimicrobial activity of lysozyme may be reduced due to its conformational changes when lysozyme is adsorbed onto a solid surface (Bower et a/., 1998). Release of lysozyme in PVOH film at ambient temperatures had a diffusion coeflficient of 3.83 X 10"^^ to 9.98 X 10"^^m^s"^ with a partition coefficient of 6 to 432 (Buonocore, 2003). Increasing the cross-linking degree decreased the diffusion coefficient and increased the partition coefficient of lysozyme. Glucose oxidase may be immobilized in a polymer matrix to confer antimicrobial activity, due to a catalysis reaction yielding hydrogen peroxide from glucose and oxygen (Appendini and Hotchkiss, 2002). Chitosan is a biopolymer with good antimicrobial abilities, because it inhibits the growth of a wide variety of fungi, yeasts and bacteria. In addition, it forms a film almost by itself after it has been dissolved in acid solution (Begin and Van Calsteren, 1999). It is a cationic polysaccharide of (3-1,4 linkages obtained by the deacetylation of chitin, which is collected from cructaceans or various fungi. Commercial chitosan products usually have a molecular weight ranging from 100 000 to 1200 000 daltons, but oligomer products with lower molecular weight can be produced by thermal, enzymatic, and/or chemical degradation (Li et al., 1997). Chitosan is readily soluble in various acidic solvents, and has high antimicrobial activity against many pathogenic and spoilage micro-organisms (Tokura et al., 1997; Tsai et al, 2002). However, the antimicrobial activity of chitosan depends on its molecular weight, and the degree of deacetylation and of chemical degradation. Tokura et al (1997) observed growth inhibition of Escherichia coli by chitosan of molecular weight 9300g/mole, but not by that of molecular weight 2200 g/mole. Tsai et al (2002) reported that the antimicrobial activity of chitosan increased with the degree of deacetylation. Both grampositive and gram-negative bacteria were inhibited by antimicrobial LDPE films incorporated with chitosan above 1.43% in LDPE (Park et a/., 2002). Chitosan incorporated in LDPE could be released into the culture broth. Chito-oligosaccharide was immobilized on PVOH by chemical cross-linking, and exhibited reduction in S. aureus bacterial counts in culture medium (Cho et al, 2000). Chitosanfilmscan also be used as a delivery system for organic acids to exhibit antimicrobial functions (Ouattarae^a/., 2000). Different plant extracts have been used for antimicrobial packaging purposes. Extracts of grapefruit seed. Rheum palmatum and Coptis chinesis have been included into LDPE films by extrusion (Chung et al, 1998; Lee et al, 1998; Ha et al, 2001). Grapefruit seed extracts in a solution form in glycerol, and in a powder form, have
114
Innovations in Food Packaging
been added in master-batch compounding for film fabrication. Other alcohoHc or aqueous plant extracts have been dried by freeze drying or spray drying, and have been blended with polymer pellets to produce films (Chung et al., 1998). The extracts retained partial antimicrobial activity after the thermal extrusion process. Grapefiiiit seed extract exhibits a wide spectrum of microbial growth inhibition, and has been reported to contain naringin, ascorbic acid, hesperidin, and various organic acids such as citric acid. In addition, in some countries it is permitted for use as a food additive (Sakamoto et ai, 1996; Lee et ai, 1998). Its water-solublefi*actionhas antimicrobial activity and contains three reactive components identified by gas chromatography (Cho et al, 1994). Sakamoto et al. (1996) identified triclosan and methyl-p-hydroxybenzote to be the active antimicrobial components in grapefinit seed extract. Kim et al. (1994) reported the existence of antimicrobial chitinase in the extract, which is stable to heat treatments. The antimicrobial activity of grapefruit seed extract was stable at high temperatures of up to 120°C (Kim and Cho, 1996), and was retained after film fabrication processes (Lee et al, 1998). Films containing grapefruit seed extracts were effective in inhibiting the growth of aerobic bacteria and/or coliforms onfi*eshproduce and on ground beef, when contact packaging was used (Chung et al., 1998; Lee et al, 1998; Ha et al, 2001). Another plant extract used for commercial antimicrobial packaging is wasabi extract, or Japanese horseradish (Koichiro, 1993). The main active antimicrobial ingredient in wasabi extract is known to be the volatile allyl isothiocyanate (AIT). The AIT gas inhibits many fiingi and bacteria. The minimal inhibition concentration of AIT against Yersinia enterocolitica and L. monocytogenes is in the range of 14-145 ppm at 10^0°C (Kusunoki et al, 1998). The extract has been encapsulated in cyclodextrin to control the volatility of AIT (Figure 7.2). The AIT in the encapsulated powder (dry form) is suggested not to be volatile, but becomes volatile when the AIT-cyclodextrin
100 Relative humidity (%) Figure 7.2 Volatility o f allyl isothiocyanate encapsulated in different matrixes. • , zeolite; • , cyclodextrin. From Koichiro (1993).
Packaging containing natural antimicrobial or antioxidative agents 1 1 5
complex is exposed to high humidity conditions after the packaging of the food product (Koichiro, 1993). The evaporated AIT then migrates to the food surface, and inhibits the growth of aerobic bacteria such as Aspergillus niger, Penicillium italicum, S. aureus, and E. coli. Stronger antimicrobial activity of AIT was reported at higher RH, suggesting that moisture has a significant fimction in AIT's antimicrobial ability (Furuya and Isshiki, 2001). The AIT-cyclodextrin complex powder has been incorporated in packaging materials of drip sheets, polyethylene films, and tablets. These products are commercially available in Japan, and are used for rice lunch boxes, meats, andfireshproduce. A design of the drip sheet is shown in Figure 7.3. Volatile components from essential oils of mustard, cinnamon, garlic and clove have been added tofilterpapers to inhibit spoilagefimgiin breads, such as Aspergillus flavus, Endomyces fibuliger, and Penicillium commune (Nielsen and Rios, 2000). Nielsen and Rios (2000) have suggested using AIT from mustard as the active component in the packaging of bread. Packaging materials incorporating a single biopreservative have limitations in ensuring the safety and extending the shelf life of foods, because they can only inhibit specific microbes. For example, nisin-incorporated packaging materials suppress the growth of gram-positive bacteria effectively (Daeschel et ah, 1992; Bower et al., 1995; Siragusa et al., 1999; An et al., 2000), but it does not work against gram-negative bacteria such as E. coli (Cha et aL, 2002). However, a narrow antimicrobial spectrum may, in certain cases, be desirable for packaged foods in which microbial contamination is caused by only a specific type of strain. Nonetheless, generally packaging materials with a wide antimicrobial spectrum are more desirable for universal use and to improve the storage stability of a variety of food products. In an effort to achieve this, Cha et al. (2002) incorporated several antimicrobial agents into films made of Na-alginate and K-carrageenan. The addition of EDTA and grapefruit seed extract to bothfilmsgave a strong inhibition against Micrococcus luteus, L. innocua, Salmonella enteritidis, E. coli, and S. aureus; however, Na-alginate based films with the addition of nisin, lysozyme, and EDTA showed the strongest inhibition against the same bacterial strains. Table 7.3 shows their Na-alginate based film results. In a similar approach, Lee et al. (2003) fabricated a paperboard coated with nisin and chitosan combinations which had been dissolved in a vinyl acetate-ethylene copolymer. Perforated polypropylene film Cyclodextrin layer with wasabi extract
Non-woven fiber layer
Figure 7.3
Design o f drip siieet incorporating wasabi extract. From Koichiro (1993).
116 Innovations in Food Packaging
Table Z 3
^f^setsiio^w^
in JMa-adginatefilmsjon several organisms
Film
Strain Micrococcus luteus Listeria innocua Salmonella enteritidis Escherichia coliStaphylococcus aureus ATCC 25923 ATCC10240 ATCC 33090 ATCC14931 ATCC 9637
Control without antimicrobial additive With nisin With lysozyme With nisin + EDTA With lysozyme + EDTA With nisin + lysozyme + EDTA With EDTA With EDTA + grapefruit seed extract With grapefruit seed extract
++ + ++ + + + ++++ ++ + ++ +
+++
+++
++ +
-++
++
+
+ +
-+
+ -1-
-, no inhibition; + , weak inhibition ( < 2 mm in inhibition zone); + + , inhibition zone o f 2-5 mm; + + + , strong inhibition with diameter > 5 mm. From Cha etal. (2002), reproduced with permission.
Nisin and chitosan migrated into water and equilibrated at about 8% for nisin and 1% for chitosan. In addition, the release rates and levels were not affected by the presence of other preservatives in the polymer coating. Nisin and chitosan in an acidified vinyl acetate-ethylene copolymer coating layer exhibited strong microbial inhibition against L monocytogenes and E. coli 0157:H7, and improved the microbial quality of milk and orange juice stored at 10°C. Cha et al. (2003) also designed chitosan films containing nisin with a strong antimicrobial activity against M luteus. Antimicrobial packaging systems containing natural antimicrobial agents can confer specific or broad microbial inhibition, depending on the agents used and their concentrations. Different types of antimicrobial-delivery mechanisms, polymers, and packaging material - food combinations may be appHed or used to maximize the effectiveness of the system.
%rTi:!OYidative p a c k a g i n g Antioxidants can be incorporated into or coated onto food packaging materials to control the oxidation of fatty components and pigments, and thus can contribute to the quality preservation of foods (Vermeiren et al, 1999). The antioxidants incorporated into plastic packaging materials may have the dual role of protecting the polymer as well as the packaged food from oxidation (Waite, 2003). Antioxidative packaging can retard the oxidative reactions of fatty ingredients in packaged foods. The incorporation of synthetic antioxidants, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), in high-density polyethylene (HDPE) liners have been shown to protect cereals from oxidation (Miltz et a/., 1988; Wessling et al, 2001). However, because of the growing concern about the use of food chemicals, there is greater interest in using
Packaging containing natural antimicrobial or antioxidative agents 117
CD O
c CO
o
CO
c o CO
•D
Time (days) Figure 7.4 Effect o f a-tocopherol-incorporated LDPE film on the oxidation o f linoleic emulsion at 6°C. • , no addition; A , added in 360 ppm; # , added in 3400 ppm. From Wessling etal. (2000), reprinted with permission o fJohn Wiley & Sons Ltd.
natural antioxidants such as a-tocopherol and ascorbic acid. In particular, a-tocopherol can be easily dissolved into polyolefins and does not break down under pol3aner processing conditions. A significant concentration of a-tocopherol also usually remains in the final plastic films (Ho et aL, 1998; Wessling et al, 1999). Zambetti et al (1995) found that the use of a-tocopherol as an antioxidant in LDPE used in extrusion coating, and in HDPE used in extrusion-blown bottles, improved the sensory performance of the bottled water by preventing the oxidation of the polymer substrates. Wessling et al. (1999) found that a-tocopherol incorporated into polypropylene (PP) retained more of its activity than when incorporated into LDPE, when bothfilmswere in contact with various foods and food-simulating liquids. The a-tocopherol in LDPE decreased at considerably higher rates with high fat-containing foods or with high-alcohol liquids. Therefore, LDPE containing an active antioxidant can offer the potential of being used as an active packaging because it can help to transfer the incorporated a-tocopherol onto the packaged foods, which will help prevent the oxidation of the food products. PP may be used as oxygen-scavenging packaging in the headspace or at the packaged foods' surface. LDPEfilmsthat incorporated a-tocopherol above 360 ppm delayed the oxidation of linoleic acid emulsions at 6°C (Figure 7.4), but did not do so at 20° and 40°C (Wessling et al, 2000). LDPE films containing a-tocopherol above 700 ppm could not prevent the oxidation of oatmeal at 20°C; this is probably due to the poor contact of the packagingfihnwith the oatmeal product (Wessling et al, 2001). For a-tocopherol-incorporated films to be effective, it is necessary that there is close contact between the packaging material and the food product. The a-tocopherol in the film is degraded chemically without volatiles being loss, while BHT diffuses out of thefilmand is volatilized on the surface, eventually migrating to the dry food (Miltz et al, 1988; Wessling et al, 2001). Another concern with a-tocopherol being incorporated into LDPE films is the potential changes it causes in the mechanical properties, color, and oxygen permeability of the film (Wessling et al, 2000).
Innovations in Food Packaging
Ascorbic acid can scavenge oxygen in the headspace air of canned or bottled products. Its ability to scavenge oxygen has made it a possible candidate for scavenging oxygen in active food packaging technologies (Smith et ah, 1995). Ascorbic acid in combination with other antioxidants can act as an antioxidant, and can retard rancidity (Yanishlieva-Maslarova, 2001). It can also protect against the peroxidation of lipid components by trapping the peroxyl radical in the aqueous phase. Due to this, the antioxidative property of ascorbic acid has been incorporated into and used in the fabrication of oxygen-scavenging plastics (Rooney, 1995). Perishable foods that are sensitive to both microbial spoilage and oxidative deterioration may be packaged in polymeric materials containing both antimicrobial and antioxidant additives. Lee et al. (2004) produced antimicrobial and antioxidant packaging materials that incorporated nisin and/or a-tocopherol. They examined their effectiveness with an emulsion model system and in milk cream. At 10°C, a-tocopherol migrated into an oil-in-water emulsion at a faster rate and reached an equilibrium level at about 6%, while nisin migrated at about 9%. Therefore, the inclusion of both a-tocopherol and nisin in coated paper could provide antimicrobial and antioxidative functions. However, no synergic or interactive effects in the antimicrobial or antioxidative activities were observed by the use of the combination (Lee et al, 2004). One application combining ascorbic acid and silver zeolite has been reported for antioxidative and antimicrobial activity (Rooney, 1995).
Antimicrobial and antioxidative packaging systems containing natural active substances may have high potential for commercial food packaging applications. Consumers would prefer to obtain better food safety of fresh produce and minimally processed foods using this type of packaging system. However, it is necessary that new active packaging systems must satisfy food safety regulations, which are different in each country. Greater food safety and quality assurance may be improved by the use of both antimicrobial and antioxidative packaging systems incorporating natural active agents. Some commercial products, such as films coated with wasabi extract, are already on the market and satisfy the regulations and consumer needs of particular countries. Most materials containing natural active agents are more effective when there is direct contact of the packaging materials with the food product. For new packaging systems to be introduced into the market effectively, careful design is required. Natural antimicrobials and antioxidants are usually costly, and therefore further development of package design using the minimum of active agents is desirable for practical applications. Food contact layers with the appropriate concentrations of the active agents may be laminated or coated onto the barrier layer of the package structure. There are some suggestions that before long many countries would adopt the new active packaging concepts into their packaging regulations. Therefore, new applications of antimicrobial and antioxidative packaging are likely to be available in the market sooner or later.
Packaging containing natural antimicrobial or antioxidative agents 1 1 9
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1 2 2 Innovations in Food Packaging
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