Jung Han. Innovations in Food Packaging

Подождите немного. Документ загружается.

Internal modified atmospheres of coated fresh fruits and vegetables

183

the physicochemical properties of the materials used as edible coatings and their

moisture sorption behavior. Using this approach will make it possible to predict their

performance once applied to a real fruit system and to tailor appropriate coatings to

achieve a target gas composition.

References

Baldwin,

E.,

Nisperos-Carriedo, M. and Baker, R. (1995). Edible coatings for lightly

processed fruits and vegetables.

Hort. Sci.

30,35-38.

Banks, N., Dadzie, B. and Cleland, D. (1993). Reducing gas exchange of fruits with sur-

face coatings.

Postharvest Biol. Technol.

3,269-284.

Banks, N., Cutting, J. and Nicholson, S. (1997). Approaches to optimizing surface coat-

ings for fruits.

NZJ Crop Hort. Sci.

25,261-272.

Ben-Yehoshua, S. and Cameron, A. (1989). Exchange determination of water vapor

carbon dioxide, oxygen, ethylene and other gases of hits and vegetables.

In:

Gases in Plant and Microbial Cells. Modern Methods of Plant Analysis,

new series 9 (H.

Linskens and J.

Jackson, eds), Springer-Verlag, New York.

pp. 178-193.

Brusewitz, G. and Singh,

(1985). Natural and applied wax coatings on oranges.

Food

Process. Preserv.

17,3 145.

Buera,

and Karel, M. (1993). Application of the

WLF

equation to describe the combined

effects of moisture and temperature on non-enzymatic browning rates in food systems.

J Food Process. Presew.

17,3145.

Elson, C., Hayes,

and Lidster,

(1985). Development of the differentially permeable fruit

coating ~utri-save@ for the modified atmosphere storage of fruit.

In:

Proceedings of

the 4th National Controlled Atmosphere Research Conference (Dept Horticultural

Science, North Carolina State University, Raleigh, NC). Horticultural Report

(S. M.

Blankenship, ed.), pp. 126,248-262.

Gontard, N., Thibault, R., Cuq, B. and Guilbert, S. (1996). Influence of relative humidity and

film composition on oxygen and carbon dioxide permeability of edible films.

J Agric.

Food Chem.

44,1064-1069.

Hagenmeier, R. and Shaw,

(1991). Permeability of shellac coatings to gases and water

vapor.

Agric. Food Chem.

39,825-829.

Hagenmeier, R. and Shaw, P. (1992). Gas permeability of fruit coating waxes.

J Am. Soc.

Hort. Sci.

117, 105-109.

Mannapperurna, J., Zagory, D., Singh,

I-?

and Kader, A. (1989). Design ofpolymeric pack-

ages for modified atmosphere storage of fresh produce. Proc. 5th Intl Controlled

Atmosphere Research Conference 14-16 June, Wenatchee, WA, Vol. 2.

Mark,

A.,

Roth, W., Mehltretter, C. and Rist, C. (1966). Oxygen permeability of amylo-

maize starch films.

Food Technol.

January, 75-77.

Mate,

and Krochta, J. M. (1996). Comparison of oxygen and water vapor permeabilities

of whey protein isolate and P-lactoglobulin edible films.

J Agric. Food Chem.

44,

3001-3004.

McHugh, T., Aujard, J. and Krochta, J.

(1994a). Plasticized whey protein edible films:

water vapor permeability properties.

J Food Sci.

59,416-41 9,423.

184

Innovations

Food Packaging

McHugh, T. and Krochta, J. M. (1994b). Sorbitol-vs glycerol-plasticized whey protein

edible films: integrated oxygen permeability and tensile property evaluation.

Agric.

Food Chem.

42,841-845.

McHugh, T. and Krochta, J. M. (1994~). Milk-protein based edible films and coatings.

Food Technol.

48,97-103.

McHugh, T., Avena-Bustillos, R. and Krochta, J. M. (1993). Hydrophilic edible films:

modified procedure for water vapor permeability and explanation of thickness

effects.

Food Sci.

58,899-903.

Meheriuk, M. and Lau,

(1988). Effect of two polymeric coatings on fruit quality of

Bartlett and dYAnjou pears.

Am. Soc. Hort. Sci.

113,222-226.

Miller, S. and Krochta, J. M. (1997). Oxygen and aroma barrier properties of edible films:

a review.

Trends Food Sci. Technol.

8,228-237.

Miller, S. and Krochta, J. M. (1998). Measuring aroma transport in polymer films.

Trans.

ASAE

41,427-433.

Miller, S., Upadhyaya, S. and Krochta, J. M. (1998). Permeability of d-limonine in whey

protein films.

Food Sci.

63,244-247.

Mujica-Paz, H. and Gontard,

(1997). Oxygen and carbon dioxide permeability of wheat

gluten film: Effect of relative humidity and temperature.

Agric. Food Chem.

45,

4101-4105.

Park, H. J., Chinnan, M. and Shewfelt, R. (1994a). Edible coating effects on storage life

and quality of tomatoes.

Food Sci.

59,568-570.

Park,

J., Bunn, J., Vergano,

and Testin, R. (1994b). Gas permeation and thickness of the

sucrose polyester Semperfi-esh coatings on apples.

Food Pm. Presew.

18,349-358.

Pauly, S. (1989). Permeability and diffusion data. In:

Polymer Handbook,

3rd edn.

(J. Brandrup and E. H. Immergut, eds), pp.

435-449. Wiley, New York,

NY.

Rico-Pena, D. and Torres, A. (1990). Oxygen transmission rate of an edible methyl

cellulose-palmitic acid film.

Food Proc. Eng.

13, 125-133.

Roos, Y. and Karel, M. (1991). Applying state diagrams to food processing and develop-

ment.

Food Technol.

45,6671, 107.

Roth, W. and Mehltretter, C. (1967). Some properties of hydroxypropylated amylomaize

starch films.

Food Technol.

21,72-74.

Shellhammer, T. and Krochta, J.

(1997). Whey protein emulsion film performance as

affected by lipid type and amount.

Food Sci.

62,39&394.

Trout, S., Hall, E. and Sykes, S. (1953). Effects of skin coatings on the behavior of apples

in storage.

Physiological and general investigations.

Aus.

Agric. Res.

4,57-81.

Modified atmosphere

packaging

ready-to-eat foods

Kevin

Spencer

Introduction

...........................................................

185

Classical nitrogen MAP

..................................................

187

ArgonMAP

........................................................... 190

harnple experiments

.....................................................

194

Results

................................................................

195

Conclusions

............................................................

201

References

......................................................... 201

Introduction

Ready-to-eat meals

Ready-to-eat meals (or ready meals) can be broadly defined as complex assemblages

of precooked foodstuffs, packaged together and sold through the refrigerated retail

chain in order to present the consumer with a rapid meal solution. They may include

such diverse items as pasta and sauce combinations, with and without the inclusion of

meat; rice-based dinners containing sauce, vegetables andlor meats; etc. Because of the

wide range of possible ingredients included, production of ready meals involves tremen-

dous operational challenges. Many different types of packaging need to be employed so

as to contain the food effectively and also present an attractive product

the consumer.

The production process for ready meals is generally located in geographically con-

centrated areas so as to provide logistical efficiencies in their distribution. This con-

centration occurs because of ready meals' high intrinsic value and cost of preparation,

but, as importantly, because of the need to maximize the shelf-life benefits that accrue

from shortening the chill transport and storage chain.

Ready meals cost more to be manufactured, but also have higher sales value than

their component parts. Due to their complexity and the

high

level of manipulation

involved in their preparation, they are also much more subject to spoilage than their

Innovations

Food Packaging

ISBN: 0-12-3

1632-5

2005 Elsevier

Ltd

All

rights

of reproduction in

any

form resewed

186

Innovations in Food

Packaging

Modified atmosphere packaging of ready-to-eat foods

187

and consideration of important common elements of basic gas packaging, a detailed

case study that describes the development of argon

MAP

in Europe will be presented.

Classical

nitrogen

MAP

Packaging foods in atmospheres containing an inert gas and carbon dioxide inhibits

both oxidative reactions and microbial spoilage. Oxidation of foods is a largely chem-

ical process driven by oxygen, which can be blocked by the displacement of oxygen

by nitrogen. Microbial spoilage is caused by the growth of microbes upon foodstuffs,

which can be blocked by the microbiocidal and microbiostatic effects of C02.

Inhibition of oxidation of food products by

MAP

Oxidation is driven by the concentration of oxygen in direct contact with reactive

chemicals within the food product (Richardson and Finley, 1985). Chemical oxidation

of foods causes deleterious degradation of the flavor, aroma, and color of foodstuffs.

Enzymatic oxidation of foods, catalyzed by lipoxygenase and oxidase, can cause

rapid degradation in product quality (Shahidi and Cadwallader, 1997). The reaction

mechanisms for both enzymatic oxidation and chemical oxidation (autoxidation and

photooxidation) of foods are well understood (Shahidi, 2000).

In order to reduce the concentration of oxygen in contact with foods, the oxygen

must be removed by vacuum andlor displaced by an inert gas. The efficiency of this

process depends upon the design of the packaging machinery, the package (design

and materials), and the physical properties of the

MAP

gas. Removal and exclusion of

oxygen by displacing air with MAP gas inhibits the rate of oxidation (Lingnert, 1992),

which directly slows the rate of degradation of valuable flavor and color components

(Civille and Dus, 1992; Shahidi, 2000). To block the oxidation entirely, however, the

complete removal of entrained and dissolved oxygen is necessary.

Air is composed of 78% nitrogen and 21% oxygen. Therefore,

MAP

mixtures based

on nitrogen are of a similar density to air. Application of nitrogen across airspaces will

introduce a great deal of turbulence as the two columns of similar density interact.

Therefore, the application of nitrogen MAP in packaging machine operations depends

upon applying sufficient force to the incoming MAP gas to both displace the air in the

package completely and overcome the turbulence that will draw in more air. The force

must be sufficient to introduce a mass of at least eight times the volume of the airspace

into the package, which makes the whole process tremendously inefficient. Applying

a vacuum cycle can increase the displacement efficiency by lowering the volume of the

air

mass which is required to be displaced. However, complete removal of the air in the

package, especially air entrained within the product itself, requires long vacuum

cycles at high vacuum. These long cycles result in concomitant damage to the pack-

age and product, and slow line speeds, as described above. There are thus two limita-

tions in nitrogen

MAP:

the inefficiency of using a large volume of nitrogen gas, and

the time requirements of vacuum cycles. These limitations cannot be overcome easily

when employing nitrogen as a

MAP

gas.

188

Innovations

Food Packaging

Nitrogen

COP: O2

MAP

for ready meals

Despite its limitations, nitrogen has been used extensively as a

MAP

gas because it is the

least expensive and the most readily available inert gas approved for use in food pack-

aging. Classical

MAP packaging utilizes combinations of nitrogen with carbon dioxide,

and oxygen (Brody, 1989b; Ooraikul and Stiles, 1991). For a wide range of food prod-

ucts, particularly chilled items such as meats and ready meals, C02 is added to nitrogen

to create MAP atmospheres (Boyd, 1997) designed to inhibit the growth of spoilage

micro-organisms, and the biochemical degradation caused by the microbial activities.

Carbon dioxide is an active agent in controlling microbes. Carbon dioxide acts by

becoming solubilized in water, where it dissociates to form carbonic acid. The result-

ing decline in pH inhibits the growth of most micro-organisms. Carbonic acid also

disrupts microbial cell membranes and inhibits respiratory enzymes directly. Carbon

dioxide is a competitive feedback inhibitor of aerobic respiration, and is especially

effective in an oxygen-starved atmosphere. Carbon dioxide thus depresses the respi-

ration in micro-organisms as well as in respiring foods (Stiles, 1991). Unlike nitrogen,

then, which is inert, carbon dioxide is highly reactive to biological systems.

Carbon dioxide controls many microbes well at concentrations above 20%, includ-

ing molds and gram-negative aerobes (e.g.,

Pseudornonas

spp.), but has been found to

be much less effective in controlling yeasts or lactic acid bacteria (e.g.

Lactobacillus

spp.) (Fierheller, 199 1).

Conditions for nitrogen MAP application for ready-to-eat products include the use

of impermeable package into which a nitrogen

C02 mixture is introduced with the

maximum possible efficiency.

order to control microbes well, the highest level of

C02 that the product can tolerate is added. For respiring products, or where the risk of

anaerobic pathogen growth is extreme, a small titer of oxygen (usually 5%) is added,

or is alternatively allowed to remain from entrained air.

MAP applications have been developed, most extensively in Europe, for a great

range of food products (Haard, 1992), including meats, produce, vegetables and fruits,

bakery, and other products (Day, 1992; Betts, 1996). MAP is used not only to confer

quality advantages, but also to ensure food safety without added risk (Anonymous,

1995). Packaging of foods in anaerobic MAP environments such as nitrogen: C02

presents no greater risk than the anaerobosis that results from temperature abuse of

sealed packages (Brody, 1989a).

Nitrogen

MAP

is a very low-cost, economical process, utilized with varying suc-

cess for many types of ready-to-eat foods (Brody, 1989b; Coulon and Louis, 1989;

Fierheller, 199 1

;

Jenkins and Harrington, 199 1). Claims for the shelf-life extension

vary among the several hundred product types currently packaged in nitrogen MAP

gas, ranging from a 5-100% longer shelf life than in air. However, most of these prod-

ucts are not, strictly speaking, ready-to-eat products. Claims for shelf-life extension of

the subset of products that are ready-to-eat are more modest, and average about

25-50% compared to the products packaged in air.

Nitrogen, C02, and O2 are all accorded GRAS status, and may be used freely, alone

or in mixtures, in the USA for food preservation. These gases are also all considered

safe for use in the European Union, and are given EU numbers. They may be used

Modified atmosphere packaging of ready-to-eat foods

189

freely providing the package is labeled as a preservative atmosphere. Argon is also

accorded GRAS status, has an EU number, and is approved for use in the EU. As dis-

cussed below, argon provides significant advantages over nitrogen in the practical

control of oxidation and spoilage micro-organism growth.

Packaging machinery

A large number of gas-packaging machinery types are currently in use around the

world, and these may be categorized generally by the basic functional process used to

prepare and seal the package. Form and fill machines create usually flexible packages

by pulling a two-dimensional film along a forming guide and sealing it into a three-

dimensional pouch. These machines can be either horizontal or vertical in format,

and can produce flexible sacks, bags, cylinders, and square or rectangular pouches.

Tray-wrapping and tray-overwrapping machines are similar in that they form a

gas-tight enclosure around or over an input tray. Tray-lidding machines accept incom-

ing preformed rigid trays and seal a gas-tight film over the tray. Thermoforming

machines create a semi-rigid package by using a heated mold to form a tray or other

pack on line, which is sealed after the introduction of the product by imposing a cov-

ering film in the case of a tray or heat-sealing the finished pack.

Buk

gas packaging

machines use large plastic sacks or other forms into which product is introduced in large

quantities and heat-seal them.

brief review of the basic types of gas packaging

machines is given in Coulon and Louis

(1989).

A more comprehensive discussion of

food packaging machinery, including illustrations, is given in Jenkins and Harrington

(1 99

65-99).

Packaging films and plastics

wide variety of metallized plastic films and paperboard products are used in MAP

packaging. Characteristics of the most commonly used materials are given in Jenkins

(1991: 35-63).

Films cited therein that are employed for gas packaging include PET,

CPET, OPP, PP, HDPE, and occasionally LPDE, PVC, and PVDC composed as

monolayers, multilayered, laminated, or metallized filmstock and trays. Among the

critical properties of these major packaging resins, the most important characteristic

for the purpose of gas packaging is their relative permeability to oxygen, carbon diox-

ide, and nitrogen or argon. The C02 and O2 gas transmission-rate properties of films

are generally well known and can be obtained from the materials specification sheets

provided by the manufacturer. The gas transmission rate may also be measured

directly by forming packages with included gas of known composition and sampling

changes over time with a commercially available oxygen andlor C02 meter. However,

accurate data on nitrogen permeabilities are less widely available, and are generally

calculated by difference measurement

that is, by measuring that which remains after

C02 and O2 have been accounted for. Permeation of argon and other gases is less well

known, but some very good data exist (Meyer

al.,

1988).

190

Innovations in Food Packaging

Gas delivery systems

MAP gases can be delivered either as pre-mixtures in cylinders, or as bulk gases to be

mixed on site. Bulk gases may be delivered as compressed gases in cylinders, or as

cryogenic liquids. Nitrogen: COz: Oz systems may also depend upon membrane-

generated gas.

A calibrated mixing panel or gas mixer is required to prepare the

appropriate MAP mixture for introduction into the gas packaging machine. In addi-

tion, valves along with pressure-regulating systems are used to step pressure down as

it passes from the source tank, through the mixer, to the point of introduction. Most

packaging machines rely upon a solenoid valve to control gas timing and mass deliv-

ery at point of pack; however, continuous form and fill machinery may use a simple

lance with appropriate pressure regulation.

Argon

MAP

Development of argon

MAP

In extensive laboratory testing, argon has been found to be superior to the MAP gases

used previously. Building upon these results, commercial development of the use of

argon gas for modified atmosphere packaging (MAP) has proceeded in Europe for a

wide range of food products (Spencer and Humphreys, 2002). Currently, over 200

products, including a wide range of ready-to-eat packaged foods, are offered at retail

in the

and elsewhere in Europe. The commercial development of argon as a MAP

gas has required the re-engineering of gas-handling systems, modification of packag-

ing equipment, and building a base of practical knowledge and detailed know-how

regarding the practical application of argon in factory environments. Considerable

engineering has been necessary to maximize the efficiency of argon use in view of its

cost, and to ensure the reliability of the product shelf-life outcome.

As discussed above, deterioration of ready-to-eat foods is caused by enzymatic and

oxidative changes over time as well as microbial spoilage. Packaging these products

in an inert gas atmosphere displaces air and hence oxygen, and thus, prevents oxida-

tion. Admixing a titer, usually 20-70%, of C02 to the inert MAP gas reduces the rate

of microbial growth.

Argon is an inert gas which has been used in modified atmosphere packaging and

processing of a variety of foodstuffs (Spencer,

1993;

Spencer and Rojak,

1993;

Spencer and Steiner,

1997).

The use of argon improves food quality for a number of

reasons. While both nitrogen and argon are inert gases, their physical properties differ

in significant ways. Since argon displaces and excludes oxygen more efficiently than

nitrogen, it provides better control against oxidation of flavor and color components

of foods. In addition, using argon results in the use of less C02 to control microbes.

As C02 is reactive and generally deleterious to product quality, the quality of the

product is better with the use of argon rather than nitrogen.

Modified atmosphere packaging of ready-to-eat foods

191

Exploiting differences between argon and nitrogen for

use in

MAP

Control of oxidation

Argon is a much denser gas

than

nitrogen, being 1.43 times as dense (1.650 vs

1.153 kg/m3). As a denser column of matter, argon can thus be made to flow in a lam-

inar fashion, like a liquid, through air space, whereas nitrogen cannot. Since air is

close in density to nitrogen (being in fact composed of 78% nitrogen), as discussed

above, nitrogen moves through airspaces inefficiently, creating much turbulence and

mixing. Without the application of great pressure to the incoming nitrogen mass, ran-

dom mixing occurs upon contact with air in a packaging tray. Thus, one volume of

incoming nitrogen will mix completely with one volume of air to displace one-half of

the air (and one-half of the oxygen). Applying 1 liter of nitrogen to a 1-liter tray of air

will change the residual oxygen from 20.8% to 10.4%; the second liter added will

drop the

to 5.2%, etc. It therefore requires eight volumes of nitrogen to bring the

residual

to substantially zero.

As a denser mass of gas, argon can be introduced into the bottom of a tray, and as

it fills the tray the argon will lift the air column upwards. If applied with minimal pres-

sure, filling the tray can be accomplished with very little mixing of argon with air.

Therefore, if properly introduced, one volume of argon can displace one volume of air

completely, resulting in a residual oxygen level of zero. In practice, between one and

two volumes of argon are used, depending upon the level of control available to the

machine operator through the gas-handling system. Thus, argon is up to eight times

more efficient than nitrogen in the filling process. While the cost of argon has been

generally four to five times higher than that of nitrogen, because of its greater effi-

ciency of use argon can be profitably employed as a

MAP

gas.

Beyond its greater efficiency, argon is also much more soluble in both water and

oils than is nitrogen, making it much more efficient at displacing entrained and dis-

solved oxygen from food media. Argon is more than three times as soluble as nitrogen

in water, and nearly twice as soluble as nitrogen in oils (Lide, 2001; Spencer and

Humphreys, 2002). It is nearly half again as soluble as oxygen in both water and oil.

Since argon is more soluble in liquids than is nitrogen, it is possible to use it to dis-

place oxygen from liquid media more rapidly, and this results in a lower final oxygen

residual level. Displacement of oxygen depends not only upon the final level of inert

gas solubilized, but also upon the rate of dissolution of inert gas into the liquid food

product. Using argon

MAP

therefore allows the use of much lower introduction pres-

sures and total volumes of applied gas, avoiding outgassing and stripping-off of

essential aroma and flavor volatiles during sparging or packaging operations.

Besides its physical effects in media, argon is also effective in controlling biologi-

cal enzymatic oxidations, whereas nitrogen is not. Argon is a competitive inhibitor of

respiratory enzymes, including oxidases (Spencer and Humphreys, 2002). Noble gases

have been shown to have an effect upon enzyme reaction rates and yields (Spencer

al.,

1995,1998), and this effect depends upon the atomic size of the noble gas. Since

192

Innovations in Food

Packaging

this effect can only be manifested if the noble gas interacts with the enzyme at the

active site, or alters the conformation of the enzyme through penetration of protein

interstices, the inhibitory effect of the gas is proportional to its molar concentration.

Additionally, argon has been shown to inhibit oxidases even when some oxygen is

present, whereas nitrogen does not. Therefore, argon can control post-harvest respiration

and also microbial respiration better than can nitrogen. Antimicrobial results for argon

alone have been shown to be particularly effective for yeasts and molds.

Contributing to argon's biological effects are other atomic properties. Argon has a

polarizability closer to oxygen than to nitrogen, and a higher ionization potential than

nitrogen. Argon has a van der Waals' constant closer to that of oxygen than of nitro-

gen, and is closer in size to oxygen than is nitrogen. These properties affect liganding

of gases to active sites, penetration of gases through membranes, and biological reac-

tion potentials. Argon has been found to behave in biological systems much more sim-

ilarly to oxygen, which is biologically reactive, than does nitrogen (Spencer

al.,

1995, 1998).

Control of microbial growth

Inclusion of C02 in

MAP

mixtures is used to control microbes which contribute

to food spoilage and shortened shelf life. While inert gases can be used to defeat

oxidative respiration, C02 is the

microstatic/microbiocidal

element of standard

MAP

mixtures. Its mode of action has been discussed above. However, C02 has deleterious

effects upon many food products, causing discoloration and other damage. It gener-

ates carbonic acid in water solution, leading to acid effects such as color changes

and production of off-tastes and aromas. C02 is also an oxidant, causing bleach-

ing effects and oxidation of volatiles and flavor components. Despite these signifi-

cant limitations, C02 is included in

MAP

because it is a very dense and quite

inexpensive gas.

Atmospheric air is composed of 20.946% oxygen, 78.084% nitrogen, and 0.934%

argon (Lide, 2001). Increasing argon concentration to high levels (70-100%) in MAP

subjects foods to a completely novel atmospheric environment. Whereas in non-living

systems carbon dioxide is a reactive gas, argon, like nitrogen, is chemically inert.

Using argon, however, allows the inclusion of lesser amounts of C02 than that

required with nitrogen MAP to achieve the desired levels of antimicrobial effects. The

same or superior levels of microbial control can therefore be achieved, while lessen-

ing the chemical and acidic side effects to food products.

Argon MAP for ready meals

Because of the physical properties discussed above, argon provides an easy solution

to the limitations of the packaging of ready meals in nitrogen-based MAP Because of

its higher density, argon flows in a laminar fashion, like a liquid, into package spaces.

Therefore, filling trays from the bottom towards the top, argon displaces air with great