Migration

Migration is defined as the transfer of chemical substances from food-contact materials (FCMs) into foodstuffs via mass transfer. This process involves the physical-chemical migration of monomers, polymerization aids, additives, or substances not intentionally added during production (NIAS) from the packaging material into the adjacent food matrix. Migration is one of the most critical quality parameters in food technology due to its potential to compromise food safety, induce toxicological effects on human health, and alter the organoleptic properties of food (taste, odor, color).

Migration is a process driven by the tendency to reach thermodynamic equilibrium and explained by kinetic principles. Fundamentally, it is a macroscopic mass transfer phenomenon modeled by Fick’s Second Law of Diffusion. The process occurs in three sequential phases:

1. Diffusion: Chemical substances (migrants) within the packaging move from the interior of the material toward the surface in contact with food, utilizing free spaces between polymer chains. This movement is driven by concentration gradients.
2. Desorption: The migrant at the polymer surface overcomes adhesive forces and transitions into an intermediate phase.
3. Adsorption: The substance in the intermediate phase is absorbed by the food matrix and distributed homogeneously or heterogeneously within the food.

The process continues until the concentration of the chemical substance in the packaging and the food becomes equal, or until chemical potential equilibrium is established.

^{Schematic diagram illustrating the migration of chemical substances (colored spheres) from packaging material into the food matrix (generated by artificial intelligence).}

The amount of substance migrating from a packaging material into food (migration rate and equilibrium) is determined by the complex interaction of internal and external factors.

• Temperature: Increased temperature enhances thermal mobility of polymer chains, creating greater free volume and exponentially increasing the diffusion coefficient. Therefore, sterilization, pasteurization, and microwave heating represent the moments of highest migration risk.
• Contact Time: According to Fick’s laws, the quantity of migrated substance increases proportionally to the square root of contact time. Products with longer shelf lives carry higher migration risks.

• Polymer Morphology: High-density and crystalline polymers (e.g., HDPE) permit less molecular migration than amorphous and low-density polymers (e.g., LDPE, PVC). Crystalline regions act as impermeable barriers to migrating molecules.
• Molecular Weight of the Migrant: Smaller, low-molecular-weight substances move more rapidly through polymer networks. According to general consensus, molecules with a molecular weight above 1000 Daltons exhibit negligible migration and are considered inert.

• The chemical nature of the food (lipophilic or hydrophilic) determines the affinity of the migrant for the food. Following the principle “like dissolves like,” fatty foods strongly promote migration because many additives in plastics are lipophilic. This phenomenon is expressed as the partition coefficient (K_P,F).

From a regulatory and analytical chemistry perspective, migration is classified into two main categories.

Total (Global) Migration: The total mass of all non-volatile substances migrating from the packaging material into food. This test assesses whether the packaging maintains an “inert” (non-reactive) character regardless of the chemical identity of the migrants. Total migration exceeding a specified limit is unacceptable as it compromises food purity.

Specific Migration: The measurement of the amount of a specific substance (e.g., monomers, plasticizers) that migrates into food. For each hazardous substance, a specific migration limit (SML) is established based on the tolerable daily intake (TDI).

• Intentionally Added Substances (IAS): Known substances intentionally incorporated into the formulation, such as monomers, antioxidants, UV stabilizers, and slip agents.
• Non-Intentionally Added Substances (NIAS - Non-Intentionally Added Substances): By-products formed during polymer synthesis or degradation, impurities, or contaminants originating from recycled materials. The identification and toxicological assessment of NIAS represent one of the greatest challenges in food safety due to their unknown structures.

The complex composition of foods (proteins, carbohydrates, fats, etc.) complicates direct measurement using analytical instruments (GC-MS, LC-MS). Therefore, standardized test liquids known as food simulants, which mimic the physical and chemical properties of foods, are used.

Tests are conducted under temperature and duration conditions simulating the “worst-case scenario” that food may encounter during its shelf life.

Chemicals migrating into food via migration can exert various effects on human health depending on the dose and duration of exposure.

• Endocrine Disruptors: Substances such as bisphenol A (BPA) and phthalates may mimic hormones in the body, leading to reproductive disorders, developmental issues, and metabolic diseases.
• Carcinogenic and Mutagenic Effects: Certain aromatic amines (particularly from adhesives in multilayer packaging) and heavy metals pose genotoxic risks.
• Bioaccumulation: Some chemicals cannot be excreted and may accumulate in tissues, leading to chronic toxicity over the long term.

In Türkiye, the safety of food packaging is ensured by the Turkish Food Codex Regulation on Food Contact Materials and Articles, which is harmonized with European Union legislation. This regulation, within the framework of Good Manufacturing Practices (GMP), requires that:

1. Human health is not endangered,
2. No unacceptable change is introduced into the composition of food,
3. The sensory properties of food are not altered.

Disclaimer: The content provided herein is for general encyclopedic informational purposes only. This information must not be used for diagnosis, treatment, or medical advice. Before making any decisions regarding health, you must consult a physician or qualified healthcare professional. The author and KÜRE Encyclopedia assume no responsibility for any consequences arising from the use of this information for diagnostic or therapeutic purposes.