Lesson- 5 Modern Packaging System
Various terms for new packaging methods can be found in the literature, such as active, smart, interactive, clever or intelligent packaging.
The definitions of active and intelligent packaging are
- Active packaging changes the condition of the packed food to extend shelflife or to improve safety or sensory properties, while maintaining the quality of the packaged food.
- Intelligent packaging systems monitor the condition of packaged foods to give information about the quality of the packaged food during transport and storage.
5.2 Active packaging
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. Packaging may be termed active when it performs some desired role in food preservation other than providing an inert barrier to external conditions. Active packaging includes additives or ‘freshness enhancers’ that are capable of scavenging oxygen, adsorbing carbon dioxide, moisture, ethylene and/or flavor/odor taints, releasing ethanol, sorbates, antioxidants and/or other preservatives and/or maintaining temperature control.
Active packaging techniques for preservation and improving quality and safety of foods can be divided into three categories; absorbers (i.e. scavengers, releasing systems and other systems. Absorbing (scavenging) systems remove undesired compounds such as oxygen, carbon dioxide, ethylene, excessive water, taints and other specific compounds. Releasing systems actively add or emit compounds to the packaged food or into the head-space of the package such as carbon dioxide, antioxidants and preservatives. Other systems may have miscellaneous tasks, such as self-heating, self-cooling and preservation. The main active packaging systems are:
5.2.1 Oxygen scavenger:
The most common oxygen scavengers take the form of small sachets containing various iron-based powders containing an assortment of catalysts. These chemical systems often react with water supplied by the food to produce a reactive hydrated metallic reducing agent that scavenges oxygen within the food package and irreversibly converts it to a stable oxide. The iron powder is separated from the food by keeping it in a small, highly oxygen permeable sachet.
5.2.2 Carbon Dioxide Scavengers/Emitters
There are many commercial sachet and label devices that can be used to either scavenge or emit carbon dioxide. The use of carbon dioxide scavengers is particularly applicable for fresh roasted or ground coffees that produce significant volumes of carbon dioxide. Fresh roasted or ground coffees cannot be left unpackaged since they absorb moisture and oxygen and lose desirable volatile aromas and flavors.
5.2.3 Ethylene Scavengers
Ethylene (C2H4) is a plant hormone that accelerates the respiration rate and subsequent senescence of horticultural products such as fruit, vegetables and flowers. Many of the effects of ethylene are necessary, e.g. induction of flowering in pineapples and colour development in citrus fruits, bananas and tomatoes, but in most horticultural situations it is desirable to remove ethylene or to suppress its effects. Effective systems utilize potassium permanganate (KMnO4) immobilized on an inert mineral substrate such as alumina or silica gel. KMnO4 oxidizes
ethylene to acetate and ethanol and in the process a change colour from purple to brown and hence indicates its remaining ethylene-scavenging capacity. KMnO4-based ethylene scavengers are available in sachets to be placed inside produce packages or inside blankets or tubes that can be placed in produce storage warehouses.
5.2.4 Ethanol Emitters
The use of ethanol as an antimicrobial agent is well documented. It is 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. The size and capacity of the ethanol-emitting sachet used depends on the weight of food, aw of the food and the shelf life required. When food is packed with an ethanol-emitting sachet, moisture is absorbed by the food and ethanol vapor is released and diffuses into the package headspace.
5.2.5 Preservative Releasers
One most commonly used preservative releaser is a synthetic silver zeolite that has been directly incorporated into food contact packaging film. The purpose of the zeolite is apparently to allow slow release of antimicrobial silver ions into the surface of food products. Many other synthetic and naturally occurring preservatives have been proposed and/or tested for antimicrobial activity in plastic and edible films. These include organic acids, e.g. propionate, benzoate and
sorbate, bacteriocins, e.g. nisin„ spice and herb extracts, e.g. from rosemary, cloves, horseradish, 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 anti-fungal agents, e.g. imazalil and benomyl. The major potential food applications for antimicrobial films include meats, fish, bread, cheese, fruit and vegetables.
5.2.6 Moisture Absorbers
Excess moisture is a major cause of food spoilage. Soaking up moisture by using various absorbers or desiccants is very effective at maintaining food quality and extending shelf life by inhibiting microbial growth and moisture-related degradation of texture and flavor. Moisture absorber sachets for humidity control in packaged dried foods, several companies manufacture moisture drip absorbent pads, sheets and blankets for liquid water control in high aw foods such as meats, fish, poultry, fruit and vegetables are available.
5.2.7 Flavour/Odor Adsorbers
The interaction of packaging with food flavors and aromas has long been recognized, especially through the undesirable flavor scalping of desirable food components. Two types of taints amenable to removal by active packaging are amines, which are formed from the breakdown of fish muscle proteins, and Aldehydes that are formed from the autoxidation of fats and oils. Volatile amines with an unpleasant smell, such as trimethylamine, associated with fish protein breakdown are alkaline and can be neutralized by various acidic compounds . The bags that are made from film containing a ferrous salt and an organic acid such as citrate or ascorbate are claimed to oxidize amines when they are absorbed by the polymer film. Odor and Taste Control (OTC) technology removes or neutralizes aldehydes.
5.3 Intelligent packaging
Intelligent packaging includes indicators to be used for quality control of packed food. They can be so-called external indicators, i.e., indicators which are attached outside the package (time temperature indicators), and so-called internal indicators which are placed inside the package, either to the head-space of the package or attached into the lid.
5.3.1 Time temperature indicator (TTI)
A time temperature indicator (TTI) can be defined as a simple device that can give the idea about easily measurable, time-temperature dependent change which affects full or partial temperature history of a food product to which it is connected. The principles of TTI operation are based on mechanical, chemical, electrochemical, enzymatic or microbiological irreversible change.
5.3.2 Freshness indicators
Two types of the changes can take place in the fresh food product i.e.
(i) Microbiological growth and metabolism resulting in pH changes, formation of toxic compounds, off-odors, gas and slime formation,
(ii) Oxidation of lipids and pigments resulting in undesirable flavors, formation of compounds with adverse biological reactions or discoloration.
A freshness indicator indicates directly the quality of the product. The indication of microbiological quality is based on a reaction between the indicator and the metabolites produced during growth of microorganisms in the product. An indicator that would show specifically the spoilage or the lack of freshness of the product, in addition to temperature abuse or package leaks, would be ideal for the quality control of packed products.
5.3.3 Pathogen indicators
Commercially available Toxin GuardTM is a system to build polyethylene-based packaging material, which is able to detect the presence of pathogenic bacteria with the aid of immobilized antibodies. As the analyte (toxin, microorganism) is in contact with the material it will be bound first to a specific, labelled antibody and then to a capturing antibody printed as a certain pattern. The method could also be applied for the detection of pesticide residues or proteins resulting from genetic modifications.