Food packaging materials and barrier properties
What food packaging must do, glass, metal, paper and plastics, barrier properties (OTR, WVTR), active and intelligent packs, sustainability, and a sum.
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Packaging is often the last line of defence for food. It keeps out microbes, insects, dirt, oxygen, moisture and light; it holds modified atmospheres; it survives transport and handling; and it tells consumers what is inside, how to use it and when to eat it by. Poor packaging shortens shelf life and wastes food, while excessive or unrecyclable packaging creates waste of its own. Choosing the right material for each product is always a balance of protection, cost, convenience and environmental impact.
Packaging materials and their properties are standard topics in food technology and dairy technology exams.
Functions of packaging
- Containment: holding the product in convenient units.
- Protection from physical damage, microbes, insects, oxygen, water vapour, light and odours.
- Preservation: enabling processes such as canning, aseptic filling, retort pouches, vacuum and modified-atmosphere packaging.
- Convenience: easy opening, reclosing, portioning, microwaving.
- Communication: labelling of ingredients, allergens, nutrition, dates, origin and instructions, as required by law.
Main materials
Glass
Inert, transparent, a complete barrier to gases and moisture, reusable and recyclable, and can be heat processed. Heavy and breakable, with high transport energy; needs coloured glass or outer cartons to protect light-sensitive foods such as beer, oils and milk.
Metals
- Tinplate (steel with a thin tin layer) and tin-free steel for cans, usually lacquered inside.
- Aluminium for beverage cans, trays and foil, a complete barrier to gases, moisture and light even when very thin.
Paper and paperboard
Cheap, light, printable, renewable and widely recycled, but a poor barrier to moisture and gases unless coated or laminated. Used for cartons, bags and corrugated boxes.
Plastics
Light, versatile and cheap, with very different barrier properties:
- Polyethylene (LDPE, LLDPE, HDPE): good moisture barrier, poor oxygen barrier; films, bags, bottles.
- Polypropylene (PP): heat resistant; tubs, films, retortable containers.
- Polyethylene terephthalate (PET): clear, strong, moderate gas barrier; bottles and trays.
- Polystyrene (PS): rigid cups and trays, and expanded foam for insulated boxes, though foam is being phased out in many places.
- Polyamide (nylon), PVDC and EVOH: high oxygen barriers, used as thin layers in multilayer films; EVOH loses barrier when wet, so it is sandwiched between moisture-resistant layers.
Laminates and composites
Combining materials gives the best of each. Aseptic beverage cartons combine paperboard (stiffness), polyethylene (sealing, moisture barrier) and aluminium foil (oxygen and light barrier), allowing UHT milk and juice to keep for months without refrigeration.
Barrier properties
- Oxygen transmission rate (OTR): volume of oxygen passing through a unit area per day, crucial for foods prone to oxidation.
- Water vapour transmission rate (WVTR): grams of water vapour per unit area per day, crucial for dry, crisp foods and for preventing moisture loss.
- Light transmission, especially ultraviolet, for milk, oils and beverages.
- Aroma and odour barrier.
Barrier properties depend on thickness, temperature, humidity and the number and quality of seals.
Modern packaging systems
- Vacuum packaging and modified-atmosphere packaging (MAP): removing or replacing air with mixtures of nitrogen, carbon dioxide and sometimes oxygen.
- Active packaging: oxygen scavengers, moisture absorbers, ethylene absorbers for fruit, CO2 emitters and antimicrobial films.
- Intelligent packaging: time–temperature indicators, freshness indicators that change colour with spoilage gases, and RFID or QR codes for traceability.
- Retort pouches and aseptic packaging for shelf-stable foods.
Safety and sustainability
- Migration: substances can move from packaging into food. Food-contact materials are regulated, with lists of permitted substances and migration limits, such as in EU Regulation 10/2011 for plastics; concerns include bisphenol A and certain plasticisers.
- Waste: packaging is a major part of municipal solid waste and plastic pollution. Responses include lighter packaging, mono-material designs that are easier to recycle, recycled content, reusable systems, and bio-based and compostable materials such as polylactic acid (PLA), which need appropriate composting facilities.
- Balancing: packaging that prevents food waste often saves more resources than it uses, since producing food usually has a larger footprint than its packaging.
Will the pack keep the product for 6 months?
A snack bag has an area of 0.05 m2 and is made from a film with an OTR of 2 cm3 per m2 per day. Tests show the product becomes noticeably rancid after absorbing about 15 cm3 of oxygen.
- Oxygen entering per day = 0.05 × 2 = 0.1 cm3.
- Time to absorb 15 cm3 = 15 ÷ 0.1 = 150 days, about 5 months.
To reach 6 months (180 days), the film's OTR must be at most 15 ÷ (180 × 0.05) ≈ 1.7 cm3 per m2 per day, or the bag must include an oxygen scavenger or be nitrogen-flushed so that less oxygen is present at the start. Warmer storage would also increase permeation and speed oxidation, so the calculation should use realistic storage temperatures.
Key points
- Packaging contains, protects, preserves, adds convenience and communicates.
- Glass and metal are complete barriers; paper needs coatings; plastics range from poor (polyethylene) to excellent (EVOH, PVDC) oxygen barriers.
- Laminates combine materials, as in aseptic cartons of paperboard, polyethylene and aluminium foil.
- Key barrier measures: OTR and WVTR; also light and aroma.
- Active packaging (scavengers, absorbers) and intelligent packaging (indicators) extend and signal shelf life.
- Food-contact safety rules limit migration; sustainability drives recyclable, reusable and bio-based materials.
What the exams ask
- School-leaving and entrance papers: functions of packaging and common materials.
- Degree and research-fellowship entrances: properties of glass, metal, paper and plastics, barrier properties, laminates, MAP, active and intelligent packaging, and migration.
- Food technology examinations: selecting packaging for specific products, shelf-life calculations from OTR and WVTR, labelling and packaging regulations, and sustainability.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Why are crisps packed in nitrogen?
Nitrogen replaces oxygen, slowing rancidity, and cushions the crisps against breakage.
Is plastic packaging always worse for the environment?
Not always. It is light, which saves transport energy, and it can greatly reduce food waste. The problems are poor recycling and leakage into the environment, so design for recycling and proper waste management matter.
Why is milk often sold in opaque containers?
Light, especially in the presence of riboflavin, causes off-flavours and destroys vitamins in milk. Opaque or tinted containers protect it.
Sources
- Robertson, G. L. Food Packaging: Principles and Practice, 3rd edition. CRC Press, 2012.
- Coles, R., McDowell, D. and Kirwan, M. J. (eds) Food Packaging Technology. Blackwell, 2003.
- Commission Regulation (EU) No 10/2011 on plastic materials and articles intended to come into contact with food. European Union, 2011.
- Yam, K. L., Takhistov, P. T. and Miltz, J. "Intelligent packaging: concepts and applications." Journal of Food Science 70, R1–R10 (2005).
- Marsh, K. and Bugusu, B. "Food packaging: roles, materials, and environmental issues." Journal of Food Science 72, R39–R55 (2007).
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