PACKAGING OF DAIRY PRODUCTS

Module 6. Modern packaging techniques

Lesson 25
ACTIVE PACKAGING

25.1 Introduction

Active packaging refers to the incorporation of certain additives into packaging film or within packaging containers with the aim of maintaining and extending product shelf life (Day, 1989). Packaging may be termed active when it performs some desired role in food preservation other than providing an inert barrier to external conditions (Rooney, 1995; Hotchkiss, 1994).

Active packaging includes additives or freshness enhancers that are capable of scavenging oxygen; adsorbing carbon dioxide, moisture, ethylene and/or flavour/odour taints; releasing ethanol, sorbates, antioxidants and/or other preservatives; and/or maintaining temperature control

Packaging material itself plays an active role in improving the shelf life of product by holding the growth of spoilage microorganisms and such packaging is called “active’, “smart”, “functional”, and “freshness preservative packaging”. Various kinds of active substances can be incorporated into the packaging materials to improve its functionality and give it an extra function. Such active packaging technologies are designed to extend the shelf life of foods while maintaining their nutritional quality and safety.

“Active packaging technologies involve interactions between the food, the packaging materials and the internal gaseous atmosphere and its main objectives are :

1. Shelf life extension

2. Easier handling

3. Preserve quality of the product

Active packaging is not synonymous with intelligent or smart packaging, which refers to packaging that senses and informs.

25.2 Active Packaging Systems

There are many varieties of active packaging techniques that are being followed. A list of techniques followed is being enlisted in the table 25.1 and are discussed in this chapter.

Table 25.1 Selected examples of active packaging systems

25.2.1 Oxygen scavengers

Oxygen scavengers were first marketed in Japan in 1976 by the Mitsubishi Gas Chemical Co. Ltd under the trade name AgelessTM. Oxygen scavengers are the most commercially important among active packaging. The common most well known oxygen scavengers are applied in the form of small sachet containing various iron based powders combined with a suitable catalyst which have capability of reducing oxygen levels to less than 0.01% in the pack. Non-metallic scavengers use organic reducing agents such as ascorbic acid, ascorbate salts or catechol. Enzymic oxygen scavenging systems are also used with either glucose oxidase or ethanol oxidase which could be incorporated into sachets, adhesive labels or immobilised onto packaging film surfaces.
Some examples of oxygen scavengers used in food industry are:

1. Laminate containing a ferrous oxygen scavenger which can be thermoformed into a tray which has been used commercially for cooked rice

2. Oxygen scavenging plastic (PET) beer bottles

3. Light activated oxygen scavenger plastic packaging materials for Beverage industry

25.2.2 Carbon dioxide scavengers/emitters

There are many commercial sachet and label devices which can be used to scavenge or to emit carbon dioxide. The use of carbon dioxide scavengers is particularly used in packing fresh roasted or ground coffees that produce significant volumes of carbon dioxide. A mixture of calcium oxide and activated charcoal has been used in polyethylene coffee pouches to scavenge carbon dioxide. Dual-action oxygen and carbon dioxide scavenger sachets and labels are more common and are commercially used for canned and foil pouched coffees in Japan and USA.Carbon dioxide emitting sachet and label devices can either be used alone or combined with an oxygen scavenger.

Dual action oxygen scavenger/carbon dioxide emitter sachets and labels are also developed, which absorb oxygen and generate an equal volume of carbon dioxide.
The main food applications for these dual-action oxygen scavenger/carbon dioxide emitter sachets and labels have been with snack food products, e.g. nuts and sponge cakes.

25.2.3 Ethylene scavengers

Ethylene (C2H4) is a plant growth regulator which accelerates the respiration rate and subsequent consequences of horticultural products such as fruits, vegetables and flowers.
Potassium Permanganate (KMnO4) immobilised on an inert mineral substrate such as alumina or silica gel. KMnO4 oxidises ethylene to acetate and ethanol and in the process changes colour from purple to brown and hence indicates its remaining ethylene scavenging capacity.

Activated carbon-based scavengers with various metal catalysts can also effectively remove ethylene.

25.2.4 Ethanol emitters

Ethanol is an antimicrobial agent particularly effective against mould but can also inhibit the growth of yeasts and bacteria. Ethanol can be sprayed directly onto food products just prior to packaging. A practical and safer method of generating ethanol is through the use of ethanol-emitting films and sachets. All of these films and sachets contain absorbed or encapsulated ethanol in a carrier material which allows the controlled release of ethanol vapour.

25.2.5 Preservative releasers

There is a potential use for antimicrobial and antioxidant packaging films which have preservative properties for extending the shelf life of a wide range of food products. Some commercial antimicrobial films and materials have been introduced, primarily in Japan. One widely reported product is a synthetic silver zeolite which is in contact with packaging film that release slowly antimicrobial silver ions into the surface of food products.

The anti microbial agents generally used on packaging materials include organic acids, e.g. propionate, benzoate and sorbate, bacteriocins, e.g. nisin, spice and herb extracts, e.g. from rosemary, cloves, horse radish, mustard, cinnamon and thyme, enzymes, e.g. peroxidase, lysozyme and glucose oxidase, chelating agents, e.g. EDTA, inorganic acids, e.g. sulphur dioxide and chlorine dioxide and antifungal agents, e.g. imazalil and benomyl. The major potential food applications for antimicrobial films include bread, cheese, fruits and vegetables.

25.2.6 Moisture absorbers

Excess moisture cause food spoilage which can be reduced by using various absorbers or desiccants which in turn helps in maintaining food quality and extending shelf life by inhibiting microbial growth and moisture related degradation of texture and flavour.

Several companies manufacture moisture-drip absorbent pads, sheets and blankets which consist of two layers of a microporous non-woven plastic film, such as polyethylene or polypropylene, between which is placed a superabsorbent polymer capable of absorbing up to 500 times its own weight of water which is used for foods such as meats, fish, poultry, fruit and vegetables. Typical superabsorbent polymers include polyacrylate salts, carboxymethyl cellulose (CMC) and starch copolymers which have a very strong affinity for water.
Moisture drip absorber pads are commonly placed under packaged fresh meats, fish and poultry to absorb unsightly tissue drip exudate. Larger sheets and blankets are used for absorption of melted ice from chilled seafood during air freight transportation, or for controlling transpiration of horticultural produce.

Microporous sachets of desiccant inorganic salts such as sodium chloride have been used for the distribution of tomatoes in USA. Another example is an innovative fibreboard box which functions as a humidity buffer on its own without relying on a desiccant insert which is used for fruits or vegetables

25.2.7 Flavour/odour adsorbers

The interaction of packaging with food flavours and aromas has long been recognised. Commercially, very few active packaging techniques have been used to selectively remove undesirable flavours and taints, but many potential opportunities exist.
Debittering of pasteurised orange juices by using cellulose triacetate or acetylated paper into orange juice packaging material. is one of the example for such methods.
BMH™ powder can be incorporated into packaging Removal of aldehydes such as hexanal and heptanal from package headspaces has its applications in foods such as snack foods, cereals, dairy products, poultry and fish.
Another packaging material which is paper-based, which absorbs odorous aldehydes in the pore interstices of the powder is manufactured by EKA Noble in co-operation with Dutch company Akzo.

25.2.8 Temperature controlled packaging

Temperature control active packaging includes the use of innovative insulating materials, self-heating and self-cooling cans.
Self-heating aluminium and steel cans and containers for coffee, tea and ready meals are heated by an exothermic reaction which occurs when lime and water positioned in the base are mixed. Self-cooling cans have also been marketed in Japan. The endothermic dissolution of ammonium nitrate and chloride in water is used to cool the product.

25.2.9 Quality indicators

Time / temperature indicators may be fixed to the package which monitors the product temperature exposure throughout the supply chain. They will indicate how long the food product was above the thresh hold temperature. They provide a non reversible record of temperature exposure that is accurate and easy to interpret.

Uses:

1. Time / temperature indicators are available in a variety of time and temperature ranges and may be used to monitor the cold chain for perishable food products.

2. To monitor the temperature exposure of sensitive food products during transportation and storage.