3. Food Packaging Interactions

Migration

• Monomers or additives moving into the food

• Can cause off-flavor sand safety problems

Absorption

• Aroma compounds, fat, organic acids and pigments moving into the polymer film

• Can cause loss of aroma intensity, development of unbalanced flavor profile and damage to the package

Mechanism of migration

1. Migrant must diffuse through the polymer matrix

2. Partition across the polymer food interface

3. Diffuse through food

What accelerates migration?

Short-contact, high temperature situations (microwaving, pasteurization)

Factors influencing diffusivity on polymer side

• Crystallinity - high crystallinity = low diffusion

• High molecular weight = lower diffusion

• Additive content

• Higher thickness = lower diffusion

• Polarity (polyester higher than polyolefinic)

• Glass transition temperature (Tg)

Effect of Tg on migration

At room temperature:

• >Tg: soft, elastic-rubber → high diffusion

• <Tg: Stiff chains - glassy (e.g. PET, PC) → Low diffusion

Bisphenol A (BPA)

• Used as a starting substance for polycarbonate (PC) plastics and epoxy resins

• Toxic and harmful at very low concentration

• PC plastic is used to manufacture refillable containers, but also in cans

• Main concern was on baby bottles in microwave

When is BPA mobilized?

BPA from can epoxy coatings only mobilizes when the can is heated above the Tg of the resin (~105C)

Factors influencing migration on migrant side

• Molecular size (smaller = faster)

• Polarity (lipophilic migrants go into fatty foods much faster)

• Volatility

Factors influencing migration on food side

• Antioxidant additives can migrate intentionally (active packaging) or unintentionally

• Butylhydroxytuluene (BHT) = a lipophilic compound used as an antioxidant food additive (E321)

• Fatty foods extract lipophilic migrants far more efficiently than aqueous foods

• This is why the EU introduces a “fat reduction factor” (FRF)

Key migrants

• Glass packaging: silicates, heavy metals

• Metal packaging: Tin dissolution from plain tinplate into tomato products is the classic example

• Paper and board: benzophene (BP) photointiator migration from UV-cured inks through cardboard into food

Class of compounds that can migrate from plastic material to food

• Residual monomer

• Plasticizer

• Antioxidants

• Residual solvents

• Low MW compounds

• Decomposition products

Key migrants and their hazards in plastics (residual monomers)

• Residual monomers!

• Vinyl chloride monomer (VCM) from PVC

• Correlation between VCM inhalation and lung cancer

• Styrene monomer from PS: taste threshold in orange juice as low as 0.2-0.3 ppm

Key migrants and their hazards in plastics (Plasticizers)

• Plasticizers are the second big category

• Phthalates (from PVC) are endocrine distruptors

Plastic regulation laws

• Migration measurement protocol

• OML = overal migration limit (60 mg/kg food or 10 mg/dm²)

• SML = specific migration limit (compound specific)

• Picture shows specific food stimulants, e.g. acetic acid is for acidic foods

Why are simulants used (for plastic regulation laws) instead of real food?

• Food is really complex, each food has a different composition

• Simulants provide a standardization

• EU legislation assumes that for packages with a capacity of 0.5-10L, 1 Kg of food is exposed to 6 dm² surface area of packaging material

  • If this does not apply you have to use a correction factor

What conditions are standardized for migration experiments?

• Contact during processing

• Contact during shelf life (see picture)

Why does orange juice in high density poly ethylene taste different after storage?

• From food to packaging

• Adsorption or Scalping

• Food components (mainly flavor compounds) are absorbed on packaging materials with consequent sever reduction of quality

• occurs due to:

  • Partitioning between food and polymer

  • Sorption into amorphous polymer regions

What affects permeability of flavor components in scalping?

• Mainly their polarity

• Non-polar = better

• Additionally the following factors also affect scalping

  • molecular size

  • polarity

  • polymer free volume