Nano-Packaging for Dairy Applications
Nano-packaging may be applied to embed and to control release of active components that can improve the shelf life of food products. Studies have reported the application of metal nanoparticles in packaging system to improve the shelf life of food and dairy products. In particular, silver, copper, titanium dioxide, and zinc oxide show considerable antimicrobial properties with potential application for food packaging (Paul and Robeson 2008). Nanoparticles can be coated or directly loaded in food-packaging materials. As an example, Longano et al. (2012) proposed a new, active packaging for application to fresh dairy products characterized by copper nanoparticles incorporated into polylactic acid. In particular, laser-generated copper nanoparticles were characterized and then tested against Pseudomonas spp., a very common microbial group able to proliferate in dairy products. Results demonstrate the antimicrobial activity of active film with copper nanoparticles compared to the control polymeric matrix. A cell load equal to 6.0 log10 CFU/mL was measured at the end of the test period in active film and
7.4 log10 CFU/mL was measured in the control film (Longano et al. 2012).
Conte et al. (2013) tested films of polylactic acid embedded with copper nanoparticles to improve the shelf life of fiordilatte. In particular, the obtained results confirmed the antimicrobial effects of copper nanoparticles without compromising main sensory attributes. To reduce the quality deterioration of fiordilatte cheese, an antimicrobial packaging system containing silver nanoparticles embedded in agar gel was designed by Incoronato et al. (2011). In particular, the active packaging system characterized by silver nanoparticles embedded in agar hydrogel promoted ions exchange between the agar and the brine solution and between the brine and the food product, thus showing an increased of cheese shelf life. In particular, silver ions were able to control microbial proliferation, without affecting the lactic acid bacteria and the sensory characteristics of the product (Incoronato et al. 2011).
Gammariello et al. (2011) proposed a packaging strategy characterized by an active coating loaded with silver nanoparticles instead of the usual brine solution, combined to modified atmosphere in the package. In order to further improve fiordilatte shelf life, the active coating loaded with silver nanoparticles and the modified atmosphere were used in presence of the common brine (Mastromatteo et al., 2015). In particular, the silver nanoparticles loaded in the edible coating prolonged the lag phase of Pseudomonas spp. and promoted a slow exponential growth; moreover, active coating exhibited a strong antimicrobial activity also against the Enterobacteria. Matak and Ajaal (2013) confirmed with scanning electron microscopy and energy-dispersive X-ray spectroscopy the presence of 1% nano-silver and 0.1% titanium dioxide nanoparticle into commercial nanocomposite food packaging containers. Moreover, the ability of the active packaging to improve food shelf life was confirmed on different foodstuffs, including soft cheese and milk powder.
In vitro tests showed that ZnO nanoparticles-coated on polyvinyl-chloride-based film exhibited a good inhibition effect on growth of E. coli and St. aureus with any antimicrobial effects against mold development (Li et al., 2009). Moreover, the ability of zinc nanoparticles coated on packaging film to preserve butter was assessed by Contreras et al. (2010). The effect of TiO2 photocatalytic activity in HDPE-based food packaging on structural and microbiological stability of short-ripened cheese was studied by Gumiero et al. (2013). The film containing 1% of TiO2 displayed degradation activity toward target organic compounds.
Studies of nanotechnology applied to food packaging were also extended to nanoscale edible coatings as thin as 5 nm wide, which are invisible to the human eye. Nano-coatings will serve as moisture, lipid, and gas barriers, as well as carriers of releasing agents of colors, flavors, antioxidants, nutrients, and antimicrobials that could increase the shelf life of food, even after the packaging is opened (Qureshi et al., 2012). Examples of nano-coating applied with plasma deposition of amorphous carbon inside PET bottles as oxygen barrier were reported in the literature. Generally, nano-coatings are characterized by nano-laminate structures that consist of two or more layers of materials with nanometer dimensions that are physically or chemically bonded to each other and it is possible to incorporate active functional agents such as antimicrobials, anti-browning agents, antioxidants, enzymes, flavors, and colors into the films. A variety of different adsorbing substances could be used to create the different layers, including protein and polysaccharides, phospholipids and colloidal particles. These functional agents would increase the shelf life and quality of foods. Nano-coatings of foods with nano-laminates are simply realized by spraying technique on food surface (McClements et al., 2005). The characterization of nano-laminate coating produced by the layer-by-layer methodology and its evaluation on the preservation of Coalho cheese, a semi-hard Brazil cheese, was proposed by Medeiros et al. (2014). The obtained results suggested that gas barrier and antibacterial properties of alginate/lysozyme nano-coating are effective to extend the shelf life of Coalho cheese. In particular, after 20 days, coated cheese showed lower values of mass loss, pH, lipidic peroxidation, microorganisms proliferation, and higher titratable acidity than the uncoated cheese.