lecture 3: food packaging interactions

what are the 3 types of interactions

1. permeation

2. migration

3. Absorption

permeation and direction

• Permeation: The exchange of gases (Oxygen, Water Vapor, ) between the environment and the food through the polymer. Both directions

migration and direction

• Migration: The movement of substances (monomers, additives) from the packaging material into the food.

Absorption aka flavor scalping

• Absorption (Flavor Scalping): The movement of food components (aroma compounds, fats, pigments) from the food into the packaging.

what mechanism is migration controlled by

Migration is a diffusion-controlled process generally modeled by Fick’s Second Law

describe ficks second law

concentration changes with time- it is time dependent

what mechanism is permeation controlled by

ficks first law

what is the mechanism for migration

1) migrant diffuses through polymer matrix

2) migrant partitions across polymer-food interafce

3) migrant diffuses through food

what is partition coefficient and what does it mean if its high or low

• Partition coefficient: K (how much migrates not speed)

•  K < 1 → prefers food → more migration

• K > 1 → prefers polymer → less migration

what is diffusion flux

• Diffusion flux (J): time across area

what factors accleerate migration

high temperatures such as microwaves and pasturisation

what is diffusion coefficient

• Dp: Difusion coefficient (how fast molecule moves)

High Dₚ → moves fast 🚀

Low Dₚ → moves slow 🐢

when do you see highest migration and lowest

Highest migration: High DP +low Kp

Lowest migration: low Dp +high Kp

what are key factors at polymer side

▪ Crystallinity,
▪ Molecular weight (Mw),
▪ Additive content
▪ Thickness
▪ Polarity (polyester higher than polyolefinic)
▪ Glass transition temperature (Tg)

does additives increase diffusivity or decrease

increase

because they are generally low molecular weight and give flexibility

give example of what fcator can reduce migration

High crystallinity and high molecular weight reduce migration by creating a more "stiff" barrier.

Above glass tranasition temp polymers are in what state

Rubbery state which has higher chain mobility and increased diffusion an dmigration

Below grass transition temperature polymers are in

glassy state woth low diffusion hence lower migration

give examples of glassy materials at room temp

PET and PC

gice examples of rubbery at room temp materials

PP and PE

Does migration increase with temp

Migration usually increases with temperature following the Arrhenius relationship. Short-contact, high-temperature events like microwaving or pasteurization can significantly accelerate migration.

which are polar vs non polar

-PET

-PLA

-PP

-LDPE

Polyesters (PET, PLA) → polar

Polyolefins (LDPE, PP) → non-polar

what happens when you add oil to food matric

scalping decreases. oily strongly dissolves limonene and competes with polymer.

do higher polarity polyesters make the food flavours such as D limonene less or more likely to leave food and enter paclage

• Example: D-limonene in citrus juice is highly lipophilic. It is absorbed much more by LDPE or PP (non-polar) than by PLA or PET (polar) due to chemical affinity.

what type of migrants move faster into fatty foods

Lipophilic migrants move into fatty foods much more efficiently.

what are key migrant factors

▪ Molecular size (smaller = faster),
▪ Polarity (lipophilic migrants go into fatty foods much faster)
▪ Volatility

Bisphenol A (BPA where is it found

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

why does retort processing matter in cans

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

aka it becomes easily migrating substance

why is BPA a concern

Toxic and harmful at very low concentration

Main concern was on baby bottles in microwave

what are key influences on food side

additives such as antioxidants

give example of antioxidant

BHT

Antioxidants like BHT which is lipophilic.

• EU introduces FRF (fat reduction factor)

what can migrate from metal packaging

Tin from metal cans

what can migrate from printing inks

• benzophenone (photoinitiators) from printing inks on paperboard.

what can migrate from glass

silicates/ heavy metals

what are key compounds that can migrate from plastic to food

1. residual monomers

2. plasticizers

3. Antioxidants

4. Residual solvents

5. Low mW compounds

6. Decomposition products

Residual monomer examples

Vinyl Chloride monomer (VCM): From PVC; linked to health risks like lung cancer.

Styrene: From Polystyrene (PS); has a low taste threshold (0.2–0.3 ppm in juice), causing off-flavors.

1.      Plasticizers

phthalates (endocrine disruptors) from PVC

what is OML

• Overall Migration Limit (OML): The total amount of all substances allowed to migrate (Max 60 mg/kg food or 10 mg/dm²).

What is SML

• Specific Migration Limit (SML): Limits for individual, potentially toxic compounds.

Why are food simulants used instead of real food

real food is too complex to standardaize

what dimensions used as standard for migration experiments

• Legislation assumes a surface-to-volume ratio of 6 dm²/kg (the "1L cube model") to standardize exposure conditions.

If contact time between food and packaging increases,
migration will

increase until equilibrium is reached