24 Packaging
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24 Packaging Packaging is an important part of all food processing operations and with some (for example canning (Chapter 12) and MAP (Chapter 20)), it is integral to the operation itself. There have been substantial developments in both materials and packaging systems over the last ten years, which have been instrumental in both reducing packaging costs and the development of novel and minimally processed foods (Chapters 9, 19 and 20). Packaging may be defined in terms of its protective role as in ‘packaging is a means of achieving safe delivery of products in sound condition to the final user at a minimum cost’ or it can be defined in business terms as ‘a techno-economic function for optimising the costs of delivering goods whilst maximising sales and profits’. The functions of packaging are: • containment – to hold the contents and keep them secure until they are used • protection – against mechanical and environmental hazards encountered during distribution and use • communication – to identify the contents and assist in selling the product. Shipping containers should also inform the carrier about the destination and any special handling or storage instructions. Some packages inform the user about method of opening and/or using the contents • machinability – to have good performance on production lines for high speed filling, closing and collating (1000 packs per min or more), without too many stoppages • convenience – throughout the production, storage and distribution system, including easy opening, dispensing and/or after-use retail containers for consumers (Paine, 1991). The main marketing considerations for a package are: • the brand image and style of presentation required for the food • flexibility to change the size and design of the containers • compatibility with methods of handling and distribution, and with the requirements of retailers. The package should be aesthetically pleasing, have a functional size and shape, retain the food in a convenient form for the customer without leakage, possibly act as a © 2000 Woodhead Publishing Limited and CRC Press LLC Packaging 463 dispenser which opens easily and recloses securely, and be suitable for easy disposal, recycling or re-use. The package design should also meet any legislative requirements concerning labelling of foods. The factors that influence the success of a package in advertising a product have been described by Head and Stewart (1989) using the acronym SCIDASL: • Standout • Content identification • Imagery • Distinctiveness • Adaptability • Suitability • Legality The most important of these is standout – the ability of a pack to compete with up to 6000 similar products, each vying for the attention of the consumer. Others, such as correct imagery, distinctiveness and suitability are each important to create, build and sustain an image for the product that is different from its competitors. Details of the advertising and promotional functions of packaging are given by Paine (1991). The technical factors that should be taken into account when selecting a packaging material for a particular product are described by Briston (1988). The requirements of packaging to protect foods for their expected shelf life are discussed in more detail in Section 24.1. The shelf life of packaged foods is controlled by the properties of the food (including water activity, pH, susceptibility to enzymic or microbiological deterioration and the requirement for, or sensitivity to, oxygen, light, carbon dioxide and moisture) and the barrier properties of the package. A summary of the packaging requirements of selected food groups is shown in Table 24.1. Packaging materials can be grouped into two main types: 1. Shipping containers which contain and protect the contents during transport and distribution, but have no marketing function. Corrugated fibreboard cases are the most widely used shipping container for 5–20 kg loads, although they are steadily being replaced by shrinkwrapped or stretch wrapped corrugated trays. Other types of shipping containers include wooden or metal cases, crates, barrels, drums and sacks. More recently, intermediate bulk containers (IBCs), including combi-bins, large boxes made from metal, plastic or corrugated fibreboard, and large bags made from woven plastic fabric, have been introduced to increase handling efficiencies and have largely displaced wooden crates and cases (see also Section 24.1.5 and Chapter 26). IBCs have a capacity between that of a bulk road tanker and 220 l drums (e.g. 1000 l containers with integral pallet and bottom discharge valve), and are mainly used for powders and liquids. Many shipping containers are expensive and therefore made to be returnable (e.g. plastic crates for milk, beer and soft drink bottles). Others (for example expanded polystyrene shipping containers) provide insulation and mechanical protection for tomatoes and grapes or cured and wet fish and are used once. The requirements of shipping containers are to: • contain products efficiently throughout the journey • protect against the climate and contamination • be compatible with the product • be easily and efficiently filled and sealed • be easily handled © 2000 Woodhead Publishing Limited and CRC Press LLC © 2000WoodheadPublishingLimitedand CRCPressLLC Table 24.1 Selection of packaging materials for different foods Packaging Glass Metal Paper/paperboard Plastic Product type a film b Bottle Pot Tray/overwrap Carton Cellulose LDPE/HDPE film OPP Jar Bottle Can Tin/push on lid Foil Tube Bag/wrap Pot Drum/tube Carton Laminated film Co-extruded film Short shelf life Baked goods bread, buns ** cakes ** Dairy products yoghurt ** milk * * * Fresh fruit/ vegetables *1 *1 Fresh meat/fish * *2 RTEc products **2 Medium/long shelf life Dried foods fruit/ vegetables ***** cereals/flour * * pulses/nuts, herbs/spices * * * Preserves jam/marmalade * * pickles/chutneys * * sauces * * Baked goods biscuits * * * * * * * * * fruit cake * * * * * * * Beverages juices/nectars * * squashes, cordials, © 2000WoodheadPublishingLimitedand CRCPressLLC wines/spirits * * beers * * carbonated drinks * * Cheese spread * * * Cooking oils * * Dairy products cheese ***** butter * * * Essences/flavours * Frozen foods vegetables, meat/fish products * ice cream *** ready meals * * * * * Margarine * * * * Mayonnaise * Pastes and pure´es tomato/garlic * * * peanut butter * * * yeast extract * Snackfoods fried, extruded **** Sugar confectioneryd * * ** **** chocolate * * * * * * * * * Sterilised foods canned * bottled * * Syrups/honey * * * * UHT milk, soups *** aAs outer containers, often laminated cartons with polythene and/or foil. bOriented polypropylene. cReady to eat. dToffee/fondant/fudge/jellies, hard boiled. 1Perforated. 2Oxygen permeable. From Fellows and Axtell (1993). 466 Food processing technology • remain securely closed in transit, open easily when required (e.g. customs inspection) and reclose securely • carry information for carriers, wholesalers, and manufacturers about contents, destination, and how to handle and open the pack. • have minimum cost • be readily disposable, re-usable or have another use. 2. Retail containers (or consumer units) which protect and advertise the food in convenient quantities for retail sale and home storage (for example metal cans, glass bottles, jars, rigid and semi-rigid plastic tubs, collapsible tubes, paperboard cartons, and flexible plastic bags, sachets and overwraps). For convenience, this section describes both shipping and retail containers in categories that reflect their material of construction. A summary of the applications of different packaging materials to food products is shown in Table 24.1. 24.1 Theory The main factors that cause deterioration of foods during storage are: • climatic influences that cause physical or chemical changes (UV light, moisture vapour, oxygen, temperature changes) • contamination (by micro-organisms, insects or soils) • mechanical forces (damage caused by impact, vibration, compression or abrasion) • pilferage, tampering or adulteration (Chapter 25). Packaging provides a barrier between the food and the environment. It controls light transmission, the rate of transfer of heat, moisture and gases, and movement of micro- organisms or insects. In addition the package should not influence the product (for example by migration of toxic compounds, by reactions between the pack and the food (Section 24.4.1) or by selection of harmful micro-organisms in the packaged food (e.g. selection of anaerobic pathogens in MAP products, Chapter 20)). Other requirements of packaging are smooth, efficient and economical operation on the production line, resistance to damage such as fractures, tears or dents caused by filling and closing equipment, loading/unloading or transportation, and not least, minimum total cost. 24.1.1 Light Light transmission is required in packages that are intended to display the contents, but is restricted when foods are susceptible to deterioration by light (for example by oxidation of lipids, destruction of riboflavin and natural pigments). The amount of light absorbed by food in a package is found using: 1 À Rf Ia IiTp 24:1 1 À Rf Rp where Ia (Cd) intensity of light absorbed by the food, Ii (Cd) intensity of incident light, Tp fractional transmission by packaging material, Rp the fraction reflected by the packaging material and Rf the fraction reflected by the food. The fraction of light transmitted by a packaging material is found using the Beer– Lambert law: © 2000 Woodhead Publishing Limited