Food Packaging Basics

Introduction

Fresh foods are naturally packaged to protect their integrity. Thick skins and hard shells or husks protect them from mechanical damage and provide a considerable degree of protection from microorganisms. In food processing, the aim of packaging is to preserve the food, but also to provide for convenient handling, transportation, storage, and to inform consumers. Food packages are either primary, secondary or tertiary packaging. Primary packaging materials comes into direct contact with the food. Therefore it is important that they are non-toxic and do not interact with the food to cause deterioration. Secondary packaging consists of the outer box that unitize and contain the primary packaging e.g. corrugated fiber boards (cardboard boxes). Tertiary packaging groups secondary cartons into pallet loads for shipping. This allows for automated handling of large loads of products and are typically moved by forklifts.

For longer shelf life, the food package should be designed to keep out extraneous materials (physical contaminants), volatiles (smelly odors), insects, light, microbes (bacteria, molds, viruses and parasites), oxygen and moisture. Of course, keeping out all of these at the same time may not be necessary. It all depends on the type of food, risks and intended shelf life of the product. More barriers will provide longer shelf life, but this must be balanced against cost.

Characteristics of Food Packaging Materials

Food packaging materials may have a combination of the following characteristics.

1. Non-toxic
2. Prevent entry of microorganisms
3. Prevent moisture loss or gain
4. Barrier to ingress of oxygen
5. Prevents ingress of odors and environmental contaminants
6. Filter out UV light
7. Resist physical damage
8. Allow customers to see the product (transparency)
9. Tamper-resistant or tamper-evident
10. Easy to open
11. Easy to dispense and reseal
12. Easy to dispose of
13. Recyclable
14. Allow easy printing of label
15. Low cost

Type of Packaging Materials

Packaging must be ideally suited for the food that it will contain. Several types of materials are available that provide unique benefits. These are discussed below.

Textiles

Textiles are materials made from cloth or fabric such as burlap bags. They are generally used for bulk storage of cereal grains, legumes and flours. They are cheap and excellent for bulk storage, transport and distribution. Because they are non-slip, they have excellent stacking characteristics. Unfortunately, they are do not provide good barrier against moisture, gas and insects.

Wood

Today, wood is mainly used for storage of wine due to its ability to interact with the product to improve flavor. The use of wood in the food industry is less common today due to problems with keeping them sanitary. They may also chip and splinter, increasing exposure of the food plant to physical hazards. Even wooden pallets are being replaced by plastic polymer pallets that are lightweight, durable, and do not rot or splinter.

Metal Cans

These may be used for both bulk storage, and retail packaging. They provide excellent barrier against moisture, light, contaminants and gasses. Manufacturing and distribution costs however, may be relatively high. Metal cans fall under three categories: tinplate, electrolytic chromium-coated steel (tin-free steel), and aluminum. Tinplated cans are steel-based cans with a thin layer of tin to help prevent corrosion and interaction with food material in the can. Tin-free steel cans have a layer of chromium instead of tin. Chromium provides superior protection against corrosion and interaction with food. Aluminum cans are alloys made up of mainly aluminum (97.8%) and other metals in smaller proportion; typically magnesium, manganese, iron, silicon, and copper. Metal cans can be three-piece or two-piece cans. Tin-plate and tin-free cans are generally three-piece while aluminum cans are two-piece. Three-piece cans consists of a top and bottom lid and a center piece which is welded at the side seam. The top and bottom are sealed to form a ‘hermetic’ double seam. Hermetic means that the seam is tight enough to prevent entry of air and microorganisms. Double seams are measured periodically in the canning operation to make sure that they meet precise standard parameters.

Since, tin may not provide adequate barrier against interaction of food with the wall of the metal container, various lacquers (side coating) may be used to give extra protection. Different lacquers have different chemical makeup. Depending on the chemical makeup, they will provide varying resistance against acids, alkalis, and temperature.

Aluminum Foil

These provide good barrier against moisture, odors, light and microorganisms, and are excellent in deflecting heat. They are also light-weight, attractive and have excellent printing characteristics.

Glass Jars

These are used to package a wide range of retail products. They are strong, and can withstand high temperatures during processing. They provide hermetic seal and are resealable and recyclable. They allow customers to see the product before buying. However, they are heavy; increasing transportation cost, and can break easily if not handled, stacked and transported with care.

Flexible Films and Rigid Plastic Containers

Several films are available that provides a range of barrier, strength, printing and sealing properties. These include cellulose and plastic polymers. Cellulose films are made from paper pulp. They are odorless, tasteless, greaseproof and biodegradable. While they are strong and puncture resistant, they are also able to tear easily allowing easy opening of package. They also provide good permeability to gas and moisture, preventing condensation in packages. Cellulose films have good application in packaging of bakery products such as bread; where movement of moisture vapor from the crumb to the crust could cause mold growth if moisture vapor is not allowed to escape. A range of polymers with a variety of unique properties are used to make flexible films and plastic containers including: ethylene vinyl acetate, polyamides, polyethylene (LDPE or HDPE), polyethylene terephthalate (PET), polypropylene, polystyrene, polyvinyl chloride and polyvinylidene chloride. These polymer films are made from petroleum which is a product of crude oil. Petroleum is first converted to ethane and propane, which are then converted to ethylene and propylene respectively. These form the basic monomers which are then polymerized into many different desired forms with the help of catalysts. The end product is in the form of polymer resins which are then used to form both flexible films and rigid plastic containers.

Paper, Paperboard and Corrugated Cardboard

These packaging are made from the same source, that is, wood pulp. They increase in degree of thickness and strength from paper to corrugated cardboard, and provide the advantage of being light-weight, printable, recyclable and biodegradable. Disadvantages are that they are not heat-sealable and provide negligible barrier to gasses.

Laminates

Flexible laminated sheets consists of several layers of packaging types such as metal foil, paperboard and polymer films. The combination of packaging types provides superior and multi-functional barrier protection than what could be gained by just using one packaging type.

Reference: Potter, N. N. & Hotchkiss, J. H. (1998). Food Science, 5th edition. New York, NY: Springer Science+Business Media LLC.