Antimicrobial Packaging of Beverages

Chapter 21

Antimicrobial Packaging of Beverages F. Palomero, A. Morata, J. Suárez-Lepe, F. Calderón and S. Benito Technical University of Madrid, Madrid, Spain

21.1  ACTIVE PACKAGING OF BEVERAGES 21.1.1 Introduction All foods are practically perishable products, susceptible to microbial contamination. Currently, one of the biggest efforts of the industry is to develop new packaging systems to ensure the commercialization of safety-enhancement products, maintaining the quality and extending the shelf life. In this sense, Wagner (1989) defined, the smart packages as those “doing more than just offer protection.” Nowadays, active packaging technology is in full development. The evolution of new innovations within this field is linked, in many cases regarding the packaging of beverages, to the formulation of new materials (Figure 1). When speaking about active packaging in the food industry, new terms are often used to describe acquired functions besides those provided in conventional packaging (Rooney, 1995; Brody, 2001; Robertson, 2006). Within this field, it is normal to talk about extra active functions or packaging systems. It is important to clearly distinguish the undesired interactions between the package and the food from those expected and desired (Hotchkiss, 1994). The Regulation (EC) 450/2009 reflects this difference by not including in the calculation of the overall migration, the one coming from active components incorporated to the package. Some of the most relevant new abilities of the active packages are the oxygen scavengers that reduce the oxygen concentrations (Teijin, 1981; Gill, 1990; Rhim and Kim, 2014) by sachet technology, as well as the permeability control provided by new manufacturing processes of plastic polymers and the use of nanoparticles. Another key ability of new active packaging technologies is the controlled and precise release of antimicrobial substances included in the packages (Matche Baldevraj and Jagadish, 2011). Finally, there are also other packages that present physical alterations in the food they contain. For example, self-heating or self-cooling cans for beverages, microwaves susceptors, and others cause desired changes in the composition of the food by incorporating some enzymatic activity in the package (for sterilization, or disposal of cholesterol or lactose content of liquid products) (Anonym, 1977, 1990; Budny, 1990). Some of these proposals have not obtained a great commercial reception yet, although they may in the future, thanks to the development of technology that will make them cost-effective. In this sense, a basic key to the development and design of active packages is the complementarity or the compatibility between the package and the food and their properties, such as water activity, storage temperature, redox potential, any loss of color, or susceptibility to oxidative phenomena (Figure 2). As Rooney (1995) has already noted, the result of this compatibility is to optimize and to extend the shelf life, the possibility of new processes, and formulations or previously nonexistent presentations. In the particular case of the active packaging of beverages or aseptic liquids, the barrier properties against gases of the packaging materials themselves are especially relevant. These properties have not generally been considered within the category of active packages. Rather, on countless occasions, they are merely the result of the adequacy of the packaging properties to a specific or particular situations, such as in the case of new formulations and developments of plastics and, more recently, nanocomposites and bio-nanocomposites, with or without antioxidant and/or antimicrobial elements. One of the most characteristic examples in the beverages field is the use of tops or seals that can reduce concentrations of oxygen headspace in beer packaging (Toyo Seikan Kaisa Ltd.; CMB Technologies).

Antimicrobial Food Packaging. http://dx.doi.org/10.1016/B978-0-12-800723-5.00021-8 © 2016 Elsevier Inc. All rights reserved.

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282   Antimicrobial Food Packaging

Functional packaging

Active packaging

Smart packaging

Food/package/atmosphere interaction

Include a response element

Physical alterations

Diagnosis technologies

• Self-heating • Self-cooling • MW encancers

• • • • • • •

Headspace

Absorbent • • • • •

TTI (Time Temperature Indicators) Thermochromic inks Freshness indicators Integrity indicators Gas sensors Moisture sensors • RFID (Radio Frequency ID) Biosensors • EAS (Electronic article surveillance) • EMID (Electromagnetic ID)

Communication technologies

Releaser • • • • •

Oxygen CO2 Ethylene Moisture Scents/Flavors

CO2 Antioxidants Antimicrobial Enzymes Scents/Flavors

FIGURE 1  Application field of functional packaging. Type of food

Requirements Chilled meats

Color loss Ready-toeat food MW

Fruits and vegetables

Retardation of ripening Oxidation / hydratation Nuts a w

Active packaging

Oxidation Aseptic liquids

Molds growth Bakery products aw

FIGURE 2  Adequacy of use of active packaging according to requirements. Adapted from Rooney (1995).

21.1.2  Active Packaging of Beverages That Cause Physical Alteration A special case in the active packaging of beverages is the use of packages that cause physical alterations to foods. In this sense, one of the first developments has been the self-cooling or self-heating packages. However, some of these packages have not obtained a great commercial reception. This is the case for the Instant Cooling Can, or I.C. can, the first self-cooling package. It was created for soft drinks by Tempra Technologies and Crown Cork and Seal in 2006. This package is based on the vacuum heat pump technology (Figure 3). Currently, there are packages that can cool the beverages that they contain, mainly in larger volume formats, but based mainly in endothermic reactions of ammonium nitrate (NH4NO3) or ammonium nitrite (NH4NO2). When dissolved in water, they absorb heat from the system.

Antimicrobial Packaging of Beverages Chapter | 21   283

Evaporator gel

Aluminum join Isolated container Heat-sink chamber Vaccum desiccant

FIGURE 3  IC can vacuum heat pump technology (Tempra Technologies, 2006) and Barney Guarino, Chairman of Tempra Techn, showing the packaging operation (The Free Lance Star, 2001).

Tin cap Polypropylene ring Drink Tin container Expanded polystyrene and tin coating Hygroscopic salt (CaO) Heat generation area

Cross cut felt Polypropylene vessel (with piston in the centre) Colored water Tin cap

FIGURE 4  Characteristic diagram of the structure and partitioning of the self-heating package. (Fast drinks. fastdrinks2go.com).

Instead, the self-heating packages are based on exothermic hydration reactions, basically of calcium monoxide (CaO) or magnesium monoxide (MgO), which, when dissolving in water, are transformed into calcium hydroxide (Ca(OH)2) and magnesium hydroxide (Mg(OH)2), respectively (Figure 4). One objection of using calcium oxide is its high hygroscopicity. Packages with this compound must show high barrier properties against water vapor passage in order to prevent the hydration of lime and the rendering of the package useless. In addition, there should be enough space to contain the entire device. There are other optimized and commercially used developments shown in Table 1, based on more efficient chemical compounds. One of the most interesting developments in this self-heating packages field is the proposal of the recently created Dutch star-up (Aestech.com). The package offers the possibility to contain a dehydrated or dried drink to infuse in a separate compartment that may contain, for example, coffee, tea, or dehydrated vegetables (Figure 5; Table 1). This can significantly increase the shelf life of the product, improve the sensory characteristics of the final product, and to reduce the use of preservatives. Furthermore, the manufacturer points out that the design and concept of the package: - - -

Decreases cost, due to the use of standard plastic packaging production; Blends dry matter at the moment of activation, not bound to premix; Offers a single button interaction, while other products require additional actions such as turning the can upside down.

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TABLE 1  Commercial Systems of Self-Heating Packages Fundamentals

Commercial Name

∆Hr (kJ/g)

Commercial Uses

Quicklime

Hot can (hotcan.com)

251

- Coffee, tea, clear soup, soup, chocolate.

CaO + H2O → CaOH2

Product/Heat Device Volume ~1.5:1 (200-136 mL)

- Ready-to-serve meals made of vegetables. Drinks2Go (fastdrinks2go.com)

- Coffee, tea, clear soup, soup, chocolate

~1:1 (200-180 mL)

Aestech self-heating packages (Aestech.nl)

- Instant-mix dehydrated beverages, coffee, tea, infant nutrition powders, etc.

2:1

- Pre-mixed beverages, coffee, tea, etc. Dry-thermic 4Al + 3SiO2 → 2Al2O2 + 3Si

Heat genie (heatgenie.com)

836.8

- Coffee, tea, clear soup, soup, chocolate

~5:1 (270-54 mL)

Moreover, another interesting approach of this package is that it tries to solve some problems related to reluctances of the consumer, regarding the perception of the package. The placement of a clear, plastic film allows the consumer to clearly check that there is not any mixture of food with the substances that promote the exothermic reaction. This cancels any consumer reluctance against the safety of this type of package (Figure 5; Aestesh personal communication).

21.1.3  Active Packaging of Beverages Based on Polymeric Plastic Films Plastic polymers are currently one of the most important resources for the packaging of food and beverages. Plastic polymers contain several additional compounds, such as catalysts of polymerization reaction, or additives that allow a change of their physical properties, like resistance, degradability, flexibility, brightness, etc. Therefore, an important difference from other packaging materials is the ability to act as vectors for the incorporation of substances that chemically or physically act or interact with the food. In this case, controlled migrations will generate. However, according European regulation, they are not to be considered in the overall migration calculation (EC Regulation No. 1935/2004 and 450/2009). In the packaging of beverages and aseptic liquids, the physical changes in the heating produced through the incorporation of microwave susceptors have interesting applications and are commercially available. Other methods, such as the alteration of the equilibrium atmosphere of the headspace through the design of plastic polymers with variable permeability against the passage of gases, are very applicable to the packaging of beverages. The removal of oxygen from the headspace, or dissolved in the liquid solution, represents a priority in the field of food technology in order to solve problems in the distribution of sensitive beverages against oxidation. In the general field of food packaging, and within the chemical alterations field, packages with oxygen-scavenging properties in the headspace have been outlined since their incorporation in sachets in Japan in 1978 (Abe and Kondoh, 1989). They are usually based on iron salts or other oxidizable compounds that are added to labels, coextruded films, or laminated. Their first commercial use in beverage packaging was in 1989 in bottle caps, for beer packaging, that were capable of absorbing oxygen from the headspace. Carbonated soft drinks contain a sugar content of up to 15° Brix, some acidifying agents, such as citric or phosphoric acid, dyes, emulsifiers, flavoring, and antimicrobials, such as sorbic benzoic acid or sulfur dioxide. These types of beverages often contain some fruits juice, tea, or are enriched with some vitamins. They are usually acid beverages, with a pH range between 3 and 4, which explains that these drinks normally do not pasteurize due to the fact that most of bacteria, pathogenic included, die quickly in them. Cola or ginger ales soft drinks present lower pHs, normally between 2.5 and 4.0, through the incorporation of ortophosphoric acid. These low pHs, together with the content of dissolved carbon dioxide, stabilize such beverages without the heat treatment.

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Remove top seal

Seal of dry matter compartment tears and the coffee mixes with water

Press button

Coffee heats up

Water mixes with CaO

Exothermal reaction

FIGURE 5  Aestech Instant-mix self-heating package (Aestech.nl).

In wines, whether carbonated or not, the alcoholic degree and the low pH greatly condition the presence of a possibly spoiling microbiota, never pathogenic. These microbiota can produce refermentation of sugars in sweet wines or those with more than 20 g/L of fermentescible sugars, as well as the emergence of some off-flavors. Only bacteria, yeast, and molds capable of growing at low pHs could cause some kind of degeneration in this kind of beverage. Although, they can hardly constitute a public health/food safety problem (Kurtzman and Fell, 1998; Di Giacomo and Gallagher, 2001; Arias et al., 2002). In this sense, some yeast are the most significant spoiling microorganisms, because they can grow at low pHs in anaerobiosis. In particular, Zygosaccharomyces bailii is also able to tolerate high quantities

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TABLE 2  Properties of Liquids and Drinks Regarding Their Microbiological Spoilage and in Relation with Oxygen Management Property

Target

Drink or Aseptic Liquid

Species

Microbiological status

Yeasts

Musts, fruit juices, soft drinks

Saccharomyces, Torulopsis, Bretanomyces, Candida, Kloeckera, Hansenula, Debaromyces, Galactomyces, Metschnikowie Pichia, Zygosaccharomyces

Fungus

Bottled waters, soft drinks

Aspergillus, Cladosporium, Muchor, Rhizopus, Fusarium

Bacteria

Wines, sugary sodas

Lactobacillus, Leuconostoc, Oenococcus, Gluconobacter

Property

Target

Drink or aseptic liquids

Molecules involved

Degradative physicochemical processes

Lipid oxidation

Milk, soups, sauces

Fat acids, lipids

Nutrient loss

Clear soups, soups, musts, fruit juices, milk

Vitamins

Pigments oxidation and color loss

Musts, wines, fruit juices, soft drinks, beers

Antocians, polyphenols

Enzymatical browning

Wines, musts, beers

Oxidized polyphenolic pigments, quinones, acetaldehydes, aldehydes

CO2 loss

Carbonated drinks, beers

COs

of preservatives and a high content of dissolved carbon dioxide. Other yeast that may cause spoilage are shown in Table 2 (Dèak and Beuchat, 1996; Battey et al., 2002). In soft drinks with variable percentages of fruit juice and musts in composition, but significantly enough to constitute an important source of nutrients (mainly a carbon source), some lactic acid bacteria (Lactobacillus o Leuconostoc) can grow, producing spoiling, browning, precipitation, olfactory defects, and/or gas (Hatcher et al., 2001). Some species of lactic bacteria are benzoic and sorbic acid-resistant and can modify the density of the fluid (ropiness) due to the production of dextranes. Regarding molds (Table 2), they can only grow in this environment when there is a certain concentration of dissolved oxygen. In noncarbonated drinks, where this circumstance may frequently occur, some species of Aspergillus, Penicillium, Mucor, or Fusarium can slowly grow, causing visual defects only detected when the product is already on the market. Drinks made from fruit juice with high concentrations of sugars and sweeteners and without preservatives are usually subjected to a heat treatment of pasteurization. These drinks can show microbiological spoilage related to the microorganisms shown in Table 2. After their heat treatment, possible microbiological spoilage may only be produced by the possible presence of very heat-resistant vegetative forms, basically ascosporous of molds of Byssochlamys, Talaromyces, and Neosartorya (Ancasi et al., 2006).

21.1.3.1  Importance of Barrier Properties Enhancement for Beverage Packaging In the packaging of beverages, the package should protect the food against light, moisture, pathogenic microorganisms, and other factors that may affect it. Furthermore, its use should be safe according to the foreseeable conditions of use. In this sense, some of the classic problems in the packaging of foods is the permeability of the packaging material, itself, against gas, and its stability against migrations (Arvanitoyannis and Bosnea, 2004; Robertson, 2006; Mercea, 2008; Finnagan, 2009). There are not fully waterproof or water-light materials against atmospheric gases, the substances contained in foods, themselves, or those that are completely inert (Duncan, 2011). Plastic packages used in the packaging of beverages should have high barrier properties against oxygen passage, and, in carbonated drinks, they also have to prevent the dissolved carbonic gas loss (Robertson, 2006). Regarding the packaging of alcoholic drinks of high degree, ceramic materials (glass) are still used, although plastics are generally more attractive for their lightness, low cost, simple processing and molding, and especially their great diversity in terms of physical properties shown according to their formulation. The most widely used plastic polymers used are polyolefins, such as polypropylene (PP), polyethylene (HDPE, LDPE), polyethylene terephthalate (PET), polystyrene (PS), and polyvinyl chloride (PVC). Their permeability against gases and the

Antimicrobial Packaging of Beverages Chapter | 21   287

passage of other small-sized molecules constitutes the most serious drawback of these materials compared with the classic ones used in the packaging of beverages (Duncan, 2011). These plastic polymers show different degrees of permeability in function of different interrelated factors, such as the degree of the polymer branching and the polarity of these side chains, the processing methodology, the molecular weight, the formulation, or the crystallization degree (Zhang et al., 2001; Yam, 2009). The use of bio-derived polysaccharide (starch) based polymers, especially interesting for their biodegradability, has been constrained in packaging of food or beverages, mainly due to their high oxygen transmission rates (OTR) in high moisture environments (Lagarón and Sánchez-García, 2009). There are not usually pure plastic polymers reaching all the specific requirements for a specific use. For this reason, multilayer films are used, which are formed by different plastic polymers with different barrier and/or structural properties, or complex mixtures extruded from them. Ethylene–vinyl alcohol (EVOH) exhibits a very low oxygen transmission rate (OTR) values under dry conditions, but under very humid conditions (relative humidity >75%) it can possess OTR values more than an order of magnitude higher. In that conditions EVOH is commonly sandwiched between two layers of highly hydrophobic polymers such as polyethylene (Kollen and Gray, 1991; Zhang et al., 1998). Many of the multilayer or coextruded plastics, which are currently used on a large number of packages, have been developed through the aforementioned methodologies. However, there is an interest in the study, development, and optimization of polymers with improved barrier properties, reduced production costs, and lower environmental impacts (Duncan, 2011; Rhim and Kim, 2014). For this reason, a lot of studies are recently focused on the development of emerging packaging technologies based on the use of nanocomposites and bio-nanocomposites (biopolymer based composites) (Johansson, 2011; Silvestre et al., 2011; Tang et al., 2012).

21.1.4  Packaging of Food and Beverages Based on Polymer Nanomaterials The use of nanotechnology on packaging consists of designing, manufacturing, and processing polymeric materials that are filled with one or two dimension particles and with a size of about 100 nm or less (Ultracki, 2004; Paul and Robertson, 2008; Sinha Ray and Bousmina, 2008). The interest of this technology lies in the possibility of developing highly efficient materials, and establishing, with great precision, the barrier properties against the passage of gases of a certain nanopolymer, basically oxygen and carbon dioxide. Furthermore, it is also possible to obtain more stable materials against ultraviolet radiation and moisture that are structurally more resistant against efforts, rubbing, and/or heat. (“Improved” PNFP) (Figure 6). Finally, nanopolymeric films are an important resource for adding a variety of additives, such as antioxidants, antifungals, antimicrobials, etc., and are therefore able to interact with the food and/or the headspace, extending self life (Han, 2000; Imran et al., 2010; Silvestre et al., 2011) (“Active” PNFP). There is a great variety of polymeric materials based on nanoparticles (Brody, 2007; Wu et al., 2002; Lagaron et al., 2004; De abreu et al., 2007; Vladimiriov, et al., 2006; Cimmino et al., 2009). Clay nanoparticles, organized in layers and separated by interlayer galleries, are basically used (Paul and Robertson, 2008; Sihna Ray and Okamoto, 2003). Depending

Water vapor, oxygen, carbon dioxide

(a)

(b)

(c)

FIGURE 6  Illustration of the gas molecules spreading in (a) plastic polymer, and the route created by inclusion of nanoplatelets in the plastic polymer matrix, (b) intercalated, and (c). Exfoliated (tortuous pathway).

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Polymer Layered silicate

Exfoliated (nanocomposite)

Phase separated (microcomposite)

Intercalated and flocculated (nanocomposite)

FIGURE 7  Illustration of the different types of nanocomposites. Adapted from Sihna Ray and Okamoto (2003).

on the clay dispersion degree, as well as the entropic and enthalpic factors during the nanocomposite preparation, different spatial and morphological arrangements can be obtained (Paiva et al., 2008) (Figure 7). Depending on the thermodynamic conditions during the preparation of nanocomposites, the dispersion degree of the clay solution, and the interactions at molecular level between the silicate layers and the plastic polymer used, compatibility is established between both different types of nanocomposites according their spatial configuration (Figure 7). Most of the efforts are currently focused on determining the necessary conditions to obtain exfoliated structures. This morphology presents major advantages regarding the possible functional properties of the material and the low requirements of the polymer (filler), being more efficient with the use of resources (Silvestre et al., 2011). When obtaining an optimal distribution of clay particles in the polymeric matrix, the permeation of gases is significantly reduced (Silvestre et al., 2011; Figure 6). Nielsen (1967) conceived the most accepted theory nowadays to explain the improvement of the barrier properties against the permeation of gases. It is focused on the tortuous path around the clay platelets, forcing the gas permeant to travel a longer path to diffuse through the film (Figure 6). Several plastic polymers and clay fillers can be used to obtain nanocomposites. The most widely plastic polymers used are polyamide, nylon, polyolefin, PS, ethyl vinyl acetate, epoxyresins polyurethane, polyamide, and PET. The most ­common clay used to manufacture nanocomposites is montmorillonite (MMT nanoplatelets), which is characterized by a density of negative surface charge compensated by sodium or calcium cations. The nanocomposite formation is complicated, due to the hydrophobic environment generated (Sihna Ray and Okamoto, 2003; Cimmino et al., 2009; Kotsilkova et al., 2007). Modified montmorillonites have been obtained by replacing these inorganic cations with organic ammonium ions, promoting the spread and homogenization of these particles in the polymer matrix. There are commercial uses that explore these benefits, mainly for soups in stand-up pouch or boil-in-the-bag formats, juices and dairy, beer bottles, and carbonated drinks (Table 3). Commercial uses of nanocomposites are shown in Table 3, where contents of nanoclay are from 2% to 8%. Above this percentage, the exfoliated distribution is difficult to obtain. Although, barrier properties against oxygen and the passage of other gases improve when nanoparticle percentage gets higher (high load) (Maul, 2005). Many studies have shown the effectiveness of these types of complex materials that limit oxygen and water vapor permeability. Nanocomposites such as Imperm of Nanocor or Aegis OX of Honeywell (Table 3) add oxygen scavengers other than clay nanoparticles to control barrier properties. According to some authors and manufacturers, themselves, this can extend the self life of polyamide bottles that are used in the packaging of beer from 6 to 12 months. This is comparable to the product self life in glass bottles (Silvestre et al., 2011; Maul, 2005). The usual self life of beer bottles in PET is about 11 weeks. Some authors consider that this period can be extended up to 30 weeks when a nanocomposite material with high barrier properties is used. In this sense, Honeywell states that the oxygen passage range can be

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TABLE 3  Polyamide Nanocomposite Products and Producers (Maul, 2005) Product

Region

Producer

Resin Base

Website

Durethan LDPU

Europe

Lanxess/Bayer Polymers

Polyamide 6

www.laxness.com

NycoNano™

United States

Nycoa

Polyamide 6

www.nycoa.net

Aegis™ NC

United States

Honeywell

Polyamide 6

www.honeywell.com

Nanoblend™

Europe

PolyOne

Polyamide 6

www.polyone.com

Nanomide™

Asia

NanoPolymer

Polyamide 6

www.nanopolimer.com

Ecobesta

Asia

Ube Industries

Polyamide 6 copolymer

www.UBE.com

Systemer

Asia

Showa Denko

Polyamide 6

www.showadenko.com

Imperm®

All

Nanocor

Polyamide 6 MXD6

www.nanocor.com

®

®

v­ irtually reduced to zero (OTR) when it is formulated in bottles with clay nanoparticles and PET, instead of nylon 6 as filler (Rhim and Kim, 2014). Other commercial uses of these materials in beer bottles, carbonated drinks, or other thermoformed packages significantly reduce permeability against oxygen. This significantly extends the self life of oxygen-sensitive products. Bayer Polymers has created a low-cost nanoclay composite for coating paperboard carton to longer keep fruit juices more fresh. SIG Chromoplats P is a new product developed by SIG that involves the use of silicon oxide particles by plasma deposition to laminate PET packaging. According to the company, this technology triples the self life of soft drinks (Silvestre et al., 2011).

21.1.4.1  Bionanocomposite Packaging Materials for Beverages Nowadays, there is an increasing interest in the use of natural biopolymers that can replace plastic polymers that come from nonbiodegradable hydrocarbons (Luckachan and Pillai, 2011; Sorrentino et al., 2007; Tang et al., 2012; Rhim and Kim, 2014). The most important limitation for the development of materials based on the use of biopolymers lies on their great sensitivity against moisture (Cabedo et al., 2006; Sorrentino et al., 2007). Thus, these materials show limited barrier properties against oxygen or water vapor passage under certain moisture conditions. Bionanocomposites have emerged in order to improve barrier properties and to obtain their application in industrial practice (Silvestre et al., 2011; Rhim et al., 2013). In this sense, bionanocomposites are complex materials similar to nanocomposites with the only particularity that, in this case, a biopolymer is used as filler (Table 4). These structures can provide active or antimicrobial properties in the same way as those similar ones formulated with nonbiodegradable plastic polymers, discussed in the following section. However, there are no commercial applications for the packaging of beverages yet. The reading of Rhim et al. (2013) is recommended for further information about bionanocomposites in the general field of food packaging.

21.1.5  Antimicrobial Metal-Based Active Packaging for Beverage Applications Most new packaging materials with antimicrobial properties for the general packaging of food (micro and nanocomposites), are designed in combination with metal particles (silver, gold, copper, and zinc), metal oxides (TiO2), organically modified nanoclays (quaternary ammonium modified MMT), natural biopolymers (chitosan), natural antimicrobial agents (nisin, thymol, carvacrol, isothiocyanate), enzymes (peroxidase, lisozimea), and their combinations. These compounds have an antimicrobial action by direct contact, but can also migrate slowly and progressively into the package. Antimicrobial packaging materials based in the addition of metal particles usually consist of the incorporation of these particles in the inert ceramic, glass, or zeolites matrix (Matsumura et al., 2003). Or, they include them in plastic polymers such as PE, PP, PS, or nylon polyamide (Del Nobile et al., 2004). Among these, the silver ion has a broad spectrum of action against gram-positive and gram-negative microorganisms. Quantities around 50-100 μg Ag+/kg (Galeano et al., 2003) have biocide effects, although their effectiveness decreases when proteins are present. In real applications, they have to be used at higher doses, around 10-100 mg Ag+/kg (Fernandez et al., 2010). Further information regarding the study, mechanism and activity of silver particles can be obtained from Duncan (2011) and Llorens et al. (2012).

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TABLE 4  Classification of Biopolymers Used in Bionanocomposites Formulation Natural Biopolymers

Synthetic Biodegradable Polymers

Produced by Microbial Fermentation

Protein

From biomass

Polyester

Soy protein isolate

Polylactic acid

Poly(hydroxyalkanoate)

Wheat protein isolate Cornzein

Poly(hydroxybutirate)

Wheat gluten Gelatine Carbohydrates

From petrochemicals

Carbohydrates

Starch

Polycaprolactone

Pullulan

Chitosan

Polyglycolic acid

Curdlan

Agar

Polyvinylalcohol

Cellulose

Carrageenan Lipids Wax Fatty acids

TABLE 5  Proposed Commercial Applications Based on the Addition of Metal Particles for the Antimicrobial Packaging of Beverages Log Reduction

Product

References

Alicyclobacillus acidoterrestris

2 log10 CFU/mL

Apple juice

Del Nobile et al. (2004) and Rhim et al. (2006)

PLA on Glass

Salmonella enterica

2-4 log10 CFU/mL

Liquid egg

LDPE

Mesophilic

Shelf life stable  28 days

Orange juice

Jin and Gurtler (2011) and Emamifar et al. (2010)

Metal

Size

Carrier

Microorganism

AgNps clusters

90 nm

PE

ZnO, nisin, AgNPs, TiO2, ZnO

Nano

Table 5 shows some of the applications proposed, based on the addition of metal particles at micro and nanoscale, for the active antimicrobial packaging of beverages.

21.2  PHYSICAL TECHNIQUES FOR COLD PASTEURIZATION OF PACKAGED BEVERAGES Several emerging technologies allow microbial control and physicochemical stability in packaged beverages. Among them, high hydrostatic pressures (HHP), pulsed electric fields (PEF), irradiation, UV-C, and pulsed light (PL) are physical techniques that maintain quality and freshness, because they are able to control microbial developments at low temperatures. The compatibility between physical alternative treatments and packaging varies when the beverage is processed or ­packaged previously to this process. These emerging techniques normally show a high compatibility with polymeric materials' integrity, due to the low temperatures used during the treatment (Table 6). They are frequently better in retort processing.

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TABLE 6  Nonthermal Treatments and Beverage Packaging

High hydrostatic pressures (HHP)

Compatibility with Packaging Materials

Advantages

Drawbacks

Changes in food quality are not perceptible in beverages

Needs flexible packaging adapted to HHP processes

High

Dose depends on food conductivity

Continuous treatment previous to packaging

High sensory quality Low alterations in plastic polymers during pressurization Pulsed electric fields (PEF)

Continuous process

Cannot be used in foods that form bubbles Needs aseptic packaging after treatment Irradiation

Continuous or batch process

Formation of oxidation off-flavors Affect to structure of packaging materials

Medium depending on radiation dose and polymer

Density and thickness affect penetration of radiation UV-C

Beverage and packaging sterilization

Low penetration. Product must be treated at depth below of 1 mm

High

High

Optimal treatment of thermo abile plastic polymers Pulsed light (PL)

Beverage and packaging sterilization

Low penetration. Product must be treated at depth below of 1 mm

Natural antimicrobials

Preservatives with ‘green’ and ‘GRAS’ status

Undesired flavors

21.2.1  HHP in Packaged Beverages The first application of HHP in food preservation was to observe milk, pressurized at more than 450 MPa, during 1 h delays, souring for at least 24 h (Hite, 1899). Currently, pressurization of 400-600 MPa for 1-5 min can be used in bottled milk to increase shelf life at an industrial scale (Trujillo et al., 2002). HHP packaged beverages include: juices, smoothies, cold soups, liquid yogurt, or derivatives with juice, milk, wines, liquors, and other products. Many of them can be found at commercial level (Table 7). HHP treatment of beverages requires flexible packaging materials, which avoid air or other gas in the headspace. This is because highly compressible fluids can reduce their volume dramatically at high pressures, deforming or breaking the package. Normally, HHP products are pressurized after packaging, and plastic bottles or bags are used for this purpose. Continuous pressurization of liquids is not available nowadays at an industrial scale. PET is frequently used in the packaging of HHP products. Migration of plastic components or copolymers under HHP conditions (400-600 MPa) is not deeply studied. However, polymers are less affected by HHP than in retorting processes (Lopez-Rubio et al., 2005). HHP treatments increase in temperature due to the adiabatic heat of compression (3 °C per 100 MPa), which means 18 °C of increase when foods are processed at 600 MPa. This temperature is released quickly during depressurization. Global migration of plastic pouches made from polyamide/polyester or polyamide/polyethylene bilayer polymers, when pressurized at 400500 MPa/20 °C/15 min, are within the acceptable range (Largeteau et al., 2010). Similar results can be found in PP and polyethylene multilayer films. An important aspect of packaging in HHP treatment is the volume of headspace to avoid delamination (Galotto et al., 2008). Some materials that are stable at 700 MPa can suffer delamination when pressurized at high temperatures (Mensitieri et al., 2013). PP/EVOH/PP coextruded multilayer structures have been found suitable for HHP processing (Lopez-Rubio et al., 2005).

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TABLE 7  Producers of Packaged HHP Beverages Shelf-Life Producer/ Brand

HHPTemperature

Country

Under Refrigeration

Product

Packaging

Website

Suja

Organic juices and smoothies

Cylindrical PET bottles (BPA free)

-

San Diego, CA 92121, USA

≈37 days

http://www.sujajuice. com/

Coldpress

Juices and smoothies

Hexagonal PET bottles (10% rPET) HDPE caps

600 MPa-4 °C

3 Lloyds Avenue, London EC3N 3DS, UK

>5 months

http://www.coldpress.co.uk/

Villa de patos

Milk, juices and smoothies

Plastic bottles

600 MPa-low temperature

Nuevo León 66254, Mexico

-

http://villadepatos. com/

Reboot your life

Juices

Plastic prismatic bottles

-

-

>54 days

http://rebootyourlife. com.au/

Romantics

Juices, smoothies, yogurt smoothies and cold soups

PET cylindrical bottles, HDPE caps

400-600 MPa-low temperature

Barcelona 08022, Spain

>30 days

http://www. romantics.es/

Ugo

Juices

Plastic bottles

600 MPa-low temperature

Ostrava, Czech Republic

-

http://www.ugo.cz/

Preshafruit

Juices

Plastic triangular bottles

-

Derrimut VIC 3030, Australia

>1 month

http://www. preshafruit.com.au/

21.2.2  PEF in Packaged Beverages PEF treatment involves very short pulses (1-5 μs) with a very high electric field (10-50 kV/cm) and frequencies of 200400 pulses/s to destroy microbial cells, mainly affecting cell envelops (membrane and cell wall), in foods. The first developments in PEF technology were done in the 1960s (Gossling, 1960), and some pioneer studies were published on the effect of electric fields in microorganisms (Hamilton and Sale, 1967; Sale and Hamilton, 1967). Industrial applications were then advanced in the 1990s (Jayaram et al., 1992; Mertens and Knorr, 1992) (Table 8). One problem derived from conventional continuous PEF processing (Figure 8a) is the expensive aseptic packaging that must be performed after the treatment. Several potential solutions have been explored to improve this; among them is the use of PEF treatment after packaging (Roodenburg, 2011). This could be an interesting trend with useful applications in the future. The so-called PEF-in-pack treatment is applied after the normal packaging of the product by direct contact

TABLE 8  Producers of Packaged PEF Beverages Shelf Life Producer/ brand

PEFTemperature

Country

Under refrigeration

Product

Packaging

Website

Hoogesteger

Juices and smoothies

Cylindrical PET bottles

Low temperature

Domineeslaan 93. 1161 BW Zwanenburg. The Netherlands

≈21 days

http://www. hoogesteger.nl/

Purepulse

Juices (carrot, apple, pineapple, tomato, orange)

Continuous/ amicrobial bottling PET bottles

Low temperature

Agro Business Park 10. 6708 PW Wageningen. The Netherlands

≈21 days

http://www. purepulse.eu/

Antimicrobial Packaging of Beverages Chapter | 21   293

Aseptic packaging

Electrodes

Electrodes PEF generator

PEF generator PEF treatment

Pump

(a)

Expedition

Expedition

PEF treatment

Packaging

Raw product

Pump

Raw product

(b)

FIGURE 8  (a) Conventional PEF process. Treatment before packaging. (b) PEF-in-pack treatment.

between the electrodes and the packaging material (Figure 8b). It has some requirements, such as the suitable design of the multilayer polymeric material of the package, in order to transmit the electric field with suitable intensity to the beverage. Packaging materials for PEF-in-pack treatments are formed by a plastic polymer matrix with some conductive particles (filler) inside of it. The intensity of the electric field transmitted inside to each portion of the liquid beverage, and therefore of the microorganism contained on it, depends on the correct distribution of the conductive filler in the neutral matrix. It also depends on the distribution of the filler on the internal side of the package in contact with the liquid (Roodenburg, 2011). Depending on the homogeneity of this filler, the treatment received by a microorganism inside the fluid can be variable. Also, another problem is the need to design electrodes that are able to apply the PEF treatment continuously to the packs, and with low energetic requirements.

21.2.3  Food Irradiation in Packaged Beverages Food irradiation has more than one century of history. The first applications started at the early beginning of the twentieth century, and the method has been deeply studied and established as safe since 1980 (Farkas and Mohácsi-Farkas, 2011). Food irradiation means the application of ionizing radiations from radioactive isotopes (allowed 60Co, 137CS in food processing), X-rays below 5 MeV, and e-beam accelerators below 10 MeV kinetic energy (Farkas, 2004). Although irradiation is extensively used for preservation of meat, fish, fruits, and vegetables, less information is published regarding the treatment of the packaging of beverages such as juices, smoothies, milk, or alcoholic drinks. However, from a technical point of view, it is possible to pasteurize by ionizing radiation packaged beverages or even in continuous flow with subsequent amicrobic packaging. Regarding packaged beverages, the maximum depth of penetration for the radiation used in the liquid must be verified. Normally, e-beam accelerators are able to process a thicknesses of 3 mm of water per 1 MeV. Therefore, a standard equipment of 10 MeV could effectively process 3 cm of liquid. However, this thickness can be increased using X-rays (>20 cm) or gamma radiations. In 2000, the National Food Processors Association (NFPA) requested the FDA to allow the use of ionizing radiation in ready-to-eat products, including grape juices (Fan, 2005). Doses lower than 1 kGy can extend the shelf life of fruit juices packaged under appropriate conditions (Niemira and Fan, 2006). Fruit juices of several types were irradiated at doses up to 5 kGy without adverse effects on sensory quality, as measured by a taste panel (Niemira, 2003). Doses higher than 5 kGy degrade the flavor of grape juice. 3-10 kGy significantly reduced the sensory quality of orange juice and apple juice (Fan et al., 2004). However, doses <2.5 kGy had no adverse effects on sensory quality of apple juice or orange juice (Niemira, 2003; Spoto et al., 1997). At higher doses, the use of antioxidants such as sorbic acid may reduce the formation of offflavors in juices (Thakur and Singh, 1993; Fan et al., 2004). When a new packaging material is used in preservation by irradiation, it has to be evaluated from a chemical, toxicological, and environmental point of view before being used in contact with food (Komolprasert et al., 2008). The amount and type of the migrants formed during the irradiation process and the factors affecting to the migration through the food must be analyzed (Table 9). Gamma irradiation >30 kGy dose produces discoloration in most monolayer and multilayer commercial materials made of PS, PP, PET, PVC/HDPE, HDPE/PA, and HDPE (Goulas et al., 2004). However, it has been shown that lower dose levels (<10 kGy) do not significantly affect the mechanical properties and overall migration levels of commercial polymeric multilayer films, such as PP, EVOH, LDPE, LLDPE, PA, and ionomer (Goulas et al., 2003). When monolayer films of LDPE and EVA copolymer and multilayer films (PET/PE/EVOH/PE) were e-beam irradiated at 5, 20, and 100 kGy doses, some volatile compounds could be detected (Riganakos et al., 1999). These compounds included aldehydes, ketones, alcohols,

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TABLE 9  Maximum Dose of Irradiation in Packaging Materials Used in Pre-Packaged Foods According to 21 CFR 179.45 Packaging Materials

Abbreviation

Maximum Dose Admitted (kGy)

Section

Kraft paper

0.5

45(b)

Glassine paper

10

Nitrocellulose-coated cellophane

10

Nylon 11 [polyamide-11]

PA11

10

Polyethylene terephthalate film

PET

10

Polyolefin film

PO

10

Polystyrene film

PS

10

Vinylidene chloride-vinyl chloride copolymer film

VCVDC

10

Wax-coated paperboard

10

Ethylene-vinyl acetate copolymer

EVA

30

Nylon 6 [polyamide-6]

PA6

60

Polyethylene film

PE

60

Vinyl chloride-vinyl acetate copolymer film

VCVA

60

45(c)

45(d)

and carboxylic acids, which were able to modify the organoleptic properties and shelf life of foods. The concentrations of these migrants were dependent on the irradiation dose. Moreover, the infrared spectra and the permeability (oxygen, water, and carbon dioxide) of these polymers were not changed by irradiation, even at high doses.

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