We encounter packaging every day but rarely consider its importance or the reason for its existence. In many cases, packaging – especially flexible packaging – is very carefully designed to undertake a number of tasks designed to present food to us in an attractive, safe and convenient way.
As long as civilization has existed, packaging and storage of food has been integral to survival. Glass, wood and earthenware pots have been used for thousands of years and over the last two hundred years, steel and tin coated steel have been used not only for containing food but also to preserve it.
Such a range of materials now available has enabled food manufacturers to fulfil the requirements of packaging summarized here. This document is designed to assist processors to choose the packaging that best suits their existing portfolio and perhaps those planned for the future. The choice of packaging material however is dependent on the required shelf life of the product, its chemical composition – each
factor is interdependent.
Summary of the Functions of Packaging:
Food Composition and Packaging Choices:
The choice of packaging for foods produced in Samoa depends very much on the nature of food. Foods are complex mixtures of chemicals that include water, fats, sugars, complex carbohydrates (starches and fibre) protein, minerals and vitamins and many other organic chemicals. The composition varies in each food and gives the food its major characteristics. Fruits for example are largely composed of water, sugars, fibre small amounts of protein and vitamins and minerals. Meats are composed of proteins, variable amounts of fat, water, some minerals and vitamins with little carbohydrate. The composition of each food determines how well it withstands attack by bacteria, moulds, viruses. Chemicals such as oxygen in the air and humidity affect deterioration. Many fruits for instance have a waxy coat (e.g. tomatoes, apples) and will last longer than fruits without (e.g. strawberries).
Foods deteriorate for two reasons:
Normal life processes
During harvesting of plant foods, life processes such as respiration and ripening continue. It is possible to slow these processes down by chilling and altering the gasses around the plant (controlled atmosphere). Seed foods such as cereals and nuts are designed to last from one season to another so they will keep well if they are kept dry and cool.
During slaughter of animal foods, life processes stop almost immediately and the tissue ceases to have a defence mechanism – especially where internal tissues are exposed. Because muscle proteins are not soluble in water, the fluids present are excellent media for bacterial attack especially at the cut surface. Hence the shelf lives of meat and fish are very short. The shell of eggs provides some protection but it is
permeable to both oxygen and water vapour and so eggs will not keep indefinitely.
Attack by microorganisms
Most foods are susceptible to microbial attack. As microorganisms attack foods they produce chemicals (metabolites) that will make the food unpleasant to taste or they will cause illness. In some instances the microorganisms themselves infect consumers causing illness and occasionally death. There comes a point at which the food becomes unacceptable and possibly dangerous. Mould is much easier to see, so
mouldy food is often discarded. The rate at which growth occurs depends on the factors listed here and the steps we take to stop these processes. Generally the rate at which microorganisms grow on foods depends on:
Plastic containers have emerged during the last century to be the most dominant form of food packaging. Building blocks for polymers are extracted from the distillation of mineral oil. They are then chemically treated so that they form long chains which may be cross linked to form sheets. Because there are so many chemicals extracted from oil, there are a great many types of chains that can be formed. If they are made from just one component they are called single component polymers. For the past 50 years, approximately 13 single polymeric films have been used for packaging either used as single sheets or in combination with each other to give an enormous range of protective properties. The industry is dynamic however, and new components and combinations are being developed continuously.
Single Component Films:
Single polymer films are made by extrusion, in which pellets of the polymer are melted and extruded under heat and pressure as a sheet or tube. Alternatively some sheets are formed by callandering in which the polymer is passed between heated rollers to form the sheet with thickness defined more acccurately. The most widely used films are listed here.
The single polymeric films are:
The polymers all have slightly different characteristics and because they are quite thin, some of the will let air, moisture and gasses through.
Even though foods have been treated to stop life processes are stopped and foods have been treated so that they will not be attacked by microorganisms, about 20% of the air around us is made up of oxygen which is a very reactive gas. It is among a number of other factors that will cause food to deteriorate. In the case of high-fat foods the oxygen will attack the oil – particularly vegetable oil and cause it to oxidise
and develop unpleasant flavours (rancidity). But the damage is not confined to fat, pale carbohydrates such as those found in the starchy staples (taro, kumala, cassava, potato and yam) can darken and proteins become tough. It is therefore, often important to protect foods by using a film or a combination of films to prevent oxygen reaching the food.
Moisture or water vapour is another component of the air around us and varies from day to day. If the water vapour in the air is high then we describe the atmosphere as humid. If raining then the relative humidity of the air is 100%..
Multiple Component Films:
Multiple polymeric films are produced by combining a number of the single polymeric films in a number of ways:
Films may be coated with other polymers to improve barrier properties or to impart heat stability. Nitrocellulose is applied to one side of cellulose film to provide a moisture barrier but to maintain oxygen permeability remains. Such coated films are tough, stretchable and less permeable to air and moisture. They are used for products that have a tendency form condensation on the inside including packed meats and bacon and sausages. They can be coated with aluminium by condensing vaporised aluminium onto the surface of the carrier polymer.
When single film packages will not provide the protection required for the time of distribution or storage in wholesale stores (shelf life), it often becomes important to stop the movement of oxygen, moisture, carbon dioxide and to protect the product form light. In these cases, additional films can be added to single films. A number of techniques are used to combine different films the simplest of which is lamination. Lamination of two or more films improves the barrier properties appearance and mechanical strength of flexible films. The most versatile method of forming is adhesive laminating in which an adhesive is applied to one surface of one film and then dried. The two films are bonded by passing through rollers. Two part adhesives are commonly used.
Co-extruded films are formed by the simultaneous extrusion of two or more films. They have three significant advantages over other types of film.
Laminated Paperboard Cartons
Very complex laminates consisting of LDLPE-paper-LDPE-aluminium-saran-LDPE are enjoying increasing use for fruit juices and UHT milk. Most commonly the cartons are purchased as a roll with the spout preformed and they are filled as the carton is formed. Some headspace is allowed to facilitate mixing and avoid spillage on opening.
The advantages of this type of package are:
Printing inks for films and papers consist of dyes which are dispersed in a blend of solvents and resin which forms a varnish. Inks may also contain extenders, plasticisers and slip agents. Solvents must be carefully removed in order to prevent odour-contamination of the food.
Three processes used to print films and papers:
Summary of Labelling Requirements:
The requirements that a food label must meet in international trade are defined in a series of codex standards on food labelling. The codex standard on labelling of pre-packaged foods and the codex guidelines on nutrition labelling are included. This is of particular importance for those companies intending for those intending to export their products. For local markets the labels must conform to the upcoming Samoan Food legislation.
In summary the general labelling requirements are:
Codex also guides the presentation of labelling information including the use of language.
Additional labelling issues for which codex guidance exists include:
For more information, please Chat with us Ask The Expert.
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