## 7 Nanotechnology in Food Science
### Packaging with Nanostructures  
A vital area within the food industry is packaging because packaging is both the container and the barrier that protects the product during storage, handling, distribution, and consumption. Materials used in packaging, such as plastics, metals, glass, paper, polymers, or combinations of them (laminated paper), are chosen according to their physical properties and chemical composition. Nanomaterial scientists have turned their attention to food packaging, intending to improve the mechanical and optical properties as well as the chemical reactivity of packaging material. At the same time, improvements in packaging have positive effects along the product distribution chain [66]; therefore, knowing the characteristics of packaging is fundamental to protecting food against the effects of light, temperature, and humidity, among other factors that can affect product quality. Packaging is exposed to mechanical damage (shock, compression, etc. ), hence the need to evaluate its effect on food. Mechanical properties can be identified on the basis of the structural changes in the material when an external force is applied, evaluated by measuring tensile strength or the modulus of elasticity (Young's modulus). This explains the relationship between stress and deformation due to the chemical structure (atomic arrangement); thus, the higher the value of Young's modulus, the greater the rigidity and the lower the deformation of the material. Mechanical resistant evaluation includes elongation at break (EAB) and tensile strength (TS) tests. The main function of a gasket is to protect against microbial contamination, permeability, and exchange of gases such as oxygen, which are the criteria for the choice of material. Water vapor permeability provides a measure of the ease with which water vapor can penetrate a material, and it indicates moisture barrier properties [67]. This phenomenon is explained by molecular diffusion or by flow through pores, and its measurement indicates the amount of water vapor transmitted per unit area and unit time; it is usually expressed as the water vapor transmission rate (WVTR) [66]. Another type of protection provided by packaging is against light; therefore, optical properties evaluate the effect of light in either inhibiting or favoring spoilage reactions such as lipid oxidation, generation of off-flavors, and degradation of nutritional compounds. In part, the changes that occur in the product are associated with the transparency of the packaging (opaque, translucent, or transparent); in this sense, the optical property is weighed by transmittance, which is determined using spectrophotometry. This property is explained by the Beer-Lambert law (T = (I\(\_\)0) = e\({}^{\text{k,z}}\)), where T is the transmittance (given in percentage), I0 and I are the intensity of transmitted and incident light, respectively, k is the absorbance, and z is the thickness of the material [66; 67; 68]. Another characteristic to consider in packaging is chemical reactivity. This characteristic describes the chemical migration of substances from the packaging into the food, which is not necessarily a negative effect, since bioactive packaging tends to release components into the product that extend the shelf life through the use of antimicrobial agents [1; 66]. In this sense, nanomaterials favor the barrier properties of packaging (mechanical, optical, and permeability) attributed to the dimensions of these nanostructures. Several works have described the use of nanoparticles, nanotubes, nanoclays, nanoparticles, nanofibers, organic materials such as polysaccharides (cellulose, starch, chitosan, gluten, polylactic acid, and polyvinyl alcohol, among others), and inorganic materials such as metal oxides (zinc oxide, copper oxide, titanium dioxide, and silicon dioxide, among others) in packaging [69].