*2.1. Food Processing (Preservation)*

As feed additives, Ag-NPs has shown to be effective in the reduction of potentially pathogenic organisms such as *E. coli* and *Clostridium perfringens* [40–43], which could reduce the use of antibiotics in livestock [43]. Additionally, some Ag-NPs have also showed effective antiparasitic activity [44–46].

Ag-NPs have also been successfully applied in water treatment by incorporating them to filters with foam or by impregnating ultrafiltration membranes [29,30]. Although the investigation of Ag-NPs as a food additive is not very widespread, attractive attempts have been made to replace the use of sulfur dioxide by the use of antimicrobial nanoparticles. This is the case in the wine industry. For example, the effectiveness of a colloidal silver complex of a size < 1 nm was studied, managing to control the growth of lactic acid bacteria [47,48]. Another study confirmed the antimicrobial activity of two coated Ag-NPs against lactic acid bacteria and other microorganisms such as *S. aureus* and *E. coli*, with potential application in winemaking [49].

#### *2.2. Food Packaging (Safety)*

Food packaging is one of the areas where nanoparticles research and use is most relevant. The need of protection against foodborne diseases and the requirement of consumers to extend the useful life of the products urged the development of antimicrobial food packaging, special packaging that releases active biocide substances in order to improve the quality of the food [50]. The use of natural substances, such as green tea and chilto extracts and essential oils in packaging materials has already been investigated [51–53] but the use of Ag-NPs would be a more effective alternative because their antimicrobial activity is greater than phytochemicals. Nanotechnology in food packaging can be divided into three categories: (*i*) active packaging, (*ii*) ecofriendly packaging, and (*iii*) smart packaging, although packaging combinations are also possible (i.e., active and ecofriendly packing). In *active packaging,* the silver nanoparticles interact directly with the food or the environment polymer matrix which can be a non-degradable polymeric film such as polyethylene (PE), polyvinyl chloride (PVC) and ethylene vinyl alcohol (EVOH) or a biodegradable edible coating film made by a polymer or a stabilizing agent (ecofriendly packaging). In addition, Ag-NPs offer a good stability and slow release rates of silver ions in stored foods which makes them suitable candidates to be used in food packaging [54]. In line with this, Yu et al. [38] demonstrated the antibacterial effect of a material composed of Ag-NPs and cellulose nanofibrils against *E. coli* and *L. monocytogenes*. Similarly, silver nanoparticles immobilized with laponite showed a good growth inhibitory activity against *E. coli*, *S. aureus*, *A. niger* and *P. citrinum* [34]. Similar effects of silver nanoparticles against chicken meat (breasts and sausages) were found. The bacterial growth of *S. aureus*, *S. typhimurium* decreased, although there were also increases in cadaverine and thiamine [32,37]. On the other hand, the protective effect of silver nanoparticles in long-term packaging of nuts has also been demonstrated. The 3% silver package achieved a significant reduction in the presence of mold and coliforms and also achieved an antioxidant effect. Finally, the silver nanoparticles had a significant effect on increasing the shelf life of nuts [55].

At the framework of food safety, smart packaging, that is, packing with biosensors for the detection of pathogens represents a novel approach for food preservation, although still under development. The operation mode is based on the union or reaction of biological components with target species (microorganisms, toxins, etc.) and the transformation into detectable signals, which leads to the rapid detection of food contaminants [56]. Examples can be found in studies such as Abbaspour et al. [57] which described a selective sandwich biosensor for the detection of *S. aureus*. Combination of fluorescent carbon points (CDF) with silver nanoparticles has been reported for the detection and elimination of bacteria such as *E. coli* and *S. aureus* at low concentrations [58]. In the same way, the conjugated polyelectrolytes (CPs)–silver nanostructure pair has showed a high detection power against *E. coli* [59].

#### *2.3. Regulation about Silver Nanoparticles Use in Foods and Food Industry Packaging (Safety)*

The panel of the European Food Safety Agency (EFSA) on food additives and sources of nutrients added to food determined that there is insufficient information on Ag to assess its risk and, therefore, in the European Union (EU), Ag-NPs are not allowed in food supplements or food packaging unless authorized. EFSA has also provided Ag migration limits from the packaging (<0.05 mg/L in water and <0.05 mg/kg in food [60,61]. Therefore, manufacturers must carry out migration evaluations as well as genotoxicity, absorption, distribution, metabolism and *in vitro* excretion tests [60,61]. With all this information, EFSA will carry out a risk assessment of the specific case to determine if that package can be marketed or not. To date there are no known products that have been approved. On the other hand, in November 2015, Regulation (EU) 2015/2283 of the European Parliament and the European Council on new foods was approved. In this regulation, it appears the definition of "artificial nanomaterial" to include, within this new category ("novel foods"), all the foods that consist or contain artificial nanomaterials [62]. In spite of this, Ag-NPs still do not appear in the legislation of allowed food additives or in the materials in contact with food. Otherwise, in the United States, these regulations are influenced by the existing regulatory restrictions on the release of silver to the environment and are the responsibility of three agencies: the Environmental Protection Agency (EPA), the Food and Drug Administration (FDA) and the agency of the Institute National Occupational Safety and Health (NIOSH). The FDA published a guide for the use of nanotechnology in food or materials in contact with them and recommended that manufacturers study and prepare a toxicological profile for each container with nanomaterials [63,64].

As mentioned above, one of the problems of using these nanoparticles in food packaging is silver migration. Echegoyén and Nerín [65] conducted an analysis of the form of silver migration, whether ions or particles, into food simulants. They demonstrated that silver migrated to food and was dependent on food and warming, with acidic foods and oven heating presenting a higher migration. However, in their study, they found that Ag migration is well below the maximum migration limits established by European Union legislation. However, other studies did not observe any temperature or time-dependent increase in the migration of Ag packaged foods [66]. Gallocchio et al. [67] tested a container with Ag-NPs to store chicken breasts and did not observe that the silver content of the breasts was higher than that allowed by the EU.
