**1.2 Sorption**

Sorption or otherwise called scalping involves the mass adsorption or absorption of integral sensory quality components of food such as Favor, Aromas, Lipids and Moisture to the or by the packaging material [12] resulting in the reduction of quality of the packaged products. Sorption in packaging system occurs through both Adsorption and Absorption procedure. Adsorption involves mass transfer from the food to the surface of the packaging material, this resulting to an increased in the concentration of the food components at the interface. Sorption of aromatic components results in degradation of quality. This phenomenon of loss in quality of food product by absorption of flavor from food by polymer or vice versa is known as 'scalping' [13]. For scalping to occur, a thermodynamically favorable condition must exist [14]. But the major concern of flavor sorption is that loss in very small amount of flavor has significant effect on quality of the stored food product depending on the component sorbed [14]. A study on packing of orange juice in glass bottles and polyethylene- laminated cardboard packages found that after 24 weeks of storage at 4°C, up to 50% of d-limonene and little aldehydes and alcohols were absorbed into polyethylene-laminated cardboard packages [15]. But, this had little/no effect on the sensory properties of the orange juice [15]. At times, sorption can result in swelling of the packaging material, leading to increased migration and permeation. Further, it can reduce the mechanical properties of the polymer [16–18]. For instance, the absorption of limonene on LDPE increased the oxygen permeability of the polymer. Flavor absorption depends on characteristics of polymer (polarity, crystallinity, chain stiffness), flavor compounds (concentration, chemical composition, polarity) and environmental and external factors like temperature, relative humidity, duration of storage and composition of food matrix [6]. For liquid foods, sorption is mainly affected by partition coefficient of flavor components, whereas for solid foods, the sorption is affected by solubility and vapor pressure of components in the polymer [19].

Similar to migration, sorption is also a diffusion process. Hence, Fick's law governs sorption as well [14]. Further, sorption process is also influenced by temperature. In general, sorption and temperature are positively related. Exceptionally, sorption and temperature are negatively correlated in few cases. For instance, sorption of vinyl chloride by dry casein particles was found to reduce with increasing temperature [17, 18]. Pressure on the other hand increases sorption process the way temperature do, the internal pressure of the packaging system reduce the mechanical quality of the packaging at a higher level, high swelling pressure of the packaging film may cause mechanical disintegration of the components of the packaging film thereby making them more available to be sorbed as such increases sorption process. Pressure level with prolonged storage condition increase sorption that is why it is generally required that a packaging material should be inert to external factors. The nature of the sorbing material also affect the rate of sorption process, with chemical (such as coding inks and surface monomers) of high reaction affinity been sorbed faster. In sorption process, the quantity of volatile component sorbed by the polymer can be measured by the parameter 'solubility' [20].

### **1.3 Effect of food-packaging interaction**

The interaction of food and packaging possess negative and positive effect to both the food and the packaging materials. When packaging components migrate from the surface of the parent package it causes withering which reduces the compact characteristics

of the package. When external environmental factors migrated into the internal packaging system, it causes physical, chemical and microbiological changes to the food. Flavors and other aromatic volatile compound easily migrate out of the package from the surface of food to the external environment through a withered package. The mass movement of vapor from surface of aqueous food causes drying which affect the organoleptic and physical characteristics of the packaged food. Movement of fillers, colorant, inks and other additive from the surface of plastic films causes dangerous toxicity effect. As described in **Figure 1** above, food-package interaction possess different adverse effect ranging from:


Food-packaging interaction as well as Food-packaging and environment interaction plays a major role on quality of the product as well as integrity of the package. These effects may have direct or indirect effect on the sensory attributes of the food product, consumer health and shelf stability of the food thereby causing a direct impact on the market value and the overall acceptability of the product as such affect business good-will. Moreover, Food and Drugs Administration of the United States (FDA) and National Agency of Food and Drugs Administration (NAFDAC, 2022) of Nigeria sets a strict legislations for a 'zero tolerance' of carcinogenic migrants, and also considered all migration compounds in food as indirect food additive. Hence, knowledge on factors affecting interaction phenomena and its effect are of high importance. In this section, factors affecting the food-packaging interaction and their possible effects on food quality are discussed.
