*Food Preservation Packaging DOI: http://dx.doi.org/10.5772/intechopen.110043*


Permeation process as explained in the **Figure 2** below follows a concentration gradient because molecules are exchanged from the region where their concentration is high to a region where their concentration is low. Therefore, generally permeation process is affected by the (i) Concentration (ii) Density (iii) Solubility (iii) Internal and External Pressure/Temperature (iv) Permeability of the packaging film (v) Time (vi) Thickness of the packaging film and (vii) Relative humidity. Permeation impact the shelf life of foods, since they gain or lose components, or undergo unwanted chemical reactions with the permeating substances, therefore offers both detrimental and positive advantage. Permeation causes unbalanced flavor profile in a flavored foods, leading to change in sensory properties of the food product therefore packaging selection should ensure packing of food products with packaging material of effective barrier properties that can protect the foods packed in them for longer time not only provide enclosure.

#### *1.1.2 Migration*

There are more than 85,000 chemicals used on consumer products [7] and more than 6000 chemicals are not to be used in food packaging that have direct contact with food [8], and all these chemical compound are prone to cause toxicity hazard if consumed when they migrated into food. Migration or otherwise called diffusion in food packaging is the movement of food substance from a region of higher concentration to a region of a lower concentration through a permeable membrane (packaging film). In food packaging, migration process involves the transfer of packaging materials from the packaging surface to the food product which causes a relative change in the original integrity/quality of the food. According to Abbes et al. [9] migration can either be global (when it involves movement from the packaging itself to the food) or specific (when only specific material moves to the food surface). Ferrara et al. [10] explain migration process in a packaging system in four steps:


Migration in food packaging is affected by (i) physico-chemical characteristics of the food (ii) Storage time (iii) Temperature (iv) packaging size (v) type of packaging material/coating (vi) type of contact (vii) mobility of the packaging migrant. Depending on the packaging materials, diverse chemical compound migrated from the surface of food packaging and affect the shelf stability of the food. An ideal packaging should be inert (non-reactive) to the food. For inert packaging materials such as stainless steel, ceramics and glass only chemicals from the interior surface of the package migrated to the food and this causes tearing/wearing of the packaging as such affect its strength and its permeation inertness. Migration occurs due to the concentration gradient of the packaging materials and or the food. Migration follows simple Fick's law which states that; as a steady state, the rate of movement of diffusing compound is proportional to the concentration gradient [9, 11].

However, to determine the extent of migration in food packaging, food simulant are used. The simulant are formulated to have exact physicochemical characteristics of the food to be packaged, they are then packaged into the packaging materials as substitute for the food analyzed for chemical migration after a stipulated length of storage. The simulant differs in types representing different types of foods; hydrophilic (water based), lipophilic (fat based) or amphiphillic foods (food of varying properties). Example, vegetable oil simulant is used to measure migration into oily foods, 10% ethanol or 3% acetic acid are used for a water based drinks, 50% ethanol solution is used as simulant for butter and other amphiphillic foods. Using simulant for the estimation of migration gives only probable estimated values which are close to the actual values. Other processes such as Chemical Risk Assessment (CRA) are conducted to determine the risk of toxicity due to chemical migration into foods; Migration Models (such as Stochastic, Probabilis tic, and Empirical) are also employed to determine the risk and extent of packaging migration.
