Nanotechnology Applied to the Dairy Sector

Cristina Costa, Matteo A. Del Nobile and Amalia Conte

Department of Agricultural Sciences, Food and Environment, University of Foggia, Italy

Nanotechnology involves technology on the nanometer scale within 100 nanometer (nm), with 1 nm equaling one-billionth of a meter (10-9 m). The physical, chemical, and biological properties of structures and systems at nanoscale are substantially different than the macroscale counterparts, due to the interactions of individual atoms and molecules, thereby offering unique and novel functional applications. As the size of the particles gets reduced to nanoscale range, there is an immense increase in the surface- to-volume ratio that increases reactivity and changes the mechanical, electrical, and optical properties of the particles.

Two major approaches can be described in nanotechnologies: top down and bottom up. The top-down approach involves starting with a larger piece of material and creates nanoparticles. For example, the antimicrobial activity of silver is improved when the size of the powder is reduced to nanometer scale (Jeong et al., 2014). On the other hand, bottom-up approach involves building of structures, atom-by-atom or molecule-bymolecule. Typically, large numbers of atoms or molecules or particles are used or created by chemical synthesis, and then arranged through naturally occurring processes into a desired structure (Ravichandran, 2010).

Many natural foods contain nanoscale components, and their properties are determined by their structure—that is, casein micelles may be useful as nano-vehicles for entrapment, protection, and delivery of sensitive hydrophobic nutraceuticals within other food products (Semo et al., 2007). Nanotechnology can be applied in all the food cycle phases and can possibly improve production processes to provide products with better characteristics and new functionalities in the food industry (Sekhon, 2010). To create new and improved food products, nanotechnology has potential applications in all aspects of food chain, including quality monitoring, food processing, and food packaging (Nethirajan and Jayas, 2011).

The development of nanosensors, able to take over microorganisms, toxins, and contaminants, allows for the monitoring the quality of food during various stages of the logistic process to guarantee product quality until the consumption. In particular,

Advances in Dairy Products, First Edition.

Edited by Francesco Conto, Matteo A. Del Nobile, Michele Faccia, Angelo V. Zambrini, and Amalia Conte. © 2018 John Wiley & Sons Ltd. Published 2018 by John Wiley & Sons Ltd.

nanosensors can provide quality assurance by tracking the food-processing chain through data capture for automatic control functions and documentation. Packaging equipped with nanosensors is also designed to track either the internal or external conditions of food products throughout the supply chain. For example, such packaging can monitor temperature or humidity over time and then provide relevant information of these conditions, such as through changing packaging color (Wesley et al., 2014). Examples of nanosensor used for quality control of milk during industrial processing are also available in the literature (Qureshi et al., 2012). In particular, nanosensors are applied to monitoring, and they control specific stages of a milk process, such as baking (Sekhon 2010). Moreover, Joung et al. (2013) developed a nano-porous membrane- based impedimetric immuno-sensor for label-free detection of bacterial pathogens, such as Escherichia coli O157:H7, in whole milk.

A major focus of current nanotechnology applications in food is the development of nanostructured food ingredients and delivery systems for nutrients and supplements. Different studies on nanotechnology are exploring the potential to nanoencapsulate and deliver nutrients directly into targeted tissues to enhance flavor, antibacterial property, and other sensory characteristics of foods (Neethirajan and Jayas, 2011). In this contest, Weir et al. (2012) suggest that adding titanium dioxide nanoparticles (TiO2) could improve texture and color of some low-fat dairy products.

The application of nanotechnology in food processing is related to different types of functional nanostructures that create novel structures and introduce new functionalities into foods (Chaudhry et al., 2011). These structures include nanoemulsions, nanoparticles, nanoencapsulation, nanoliposomes, and nanofibers. Nanostructures are used to provide antimicrobial compounds, taste masking, controlled release, and better dispersion for water-insoluble food ingredients and additives (Chaudhry et al., 2011). Nanostructures protect the bioactive compounds from interaction with food ingredients, keeping their functional properties and preventing the deterioration of the food itself (i.e., oxidation of fat), and reducing the impact on food sensorial properties. Studies have reported that the application of nanostructure improves food shelf life as nano-encapsulated antimicrobial compounds for fruit juice (Sugumar et al., 2015; Ghosh et al., 2013; Donsi et al., 2011), meat products (Ramachandraiah et al., 2015) and dairy products (Shah et al., 2013; Balcao et al., 2013) and nano-encapsulation of antioxidant for hazelnut paste (Spigno et al., 2013).

The application of nanotechnology in food packaging opens new possibilities for improving packaging materials properties by adding reinforcing compounds to polymers to enhance their thermal, mechanical, barrier, and antimicrobial properties (Sorrentino et al., 2007). Nanocomposites can improve mechanical strength; reduce weight; increase heat resistance; and improve barrier against oxygen, carbon dioxide, ultraviolet radiation, moisture, and volatiles of food package materials.

Most food packaging applications developed to date incorporate metal or oxide nanoparticles or more commonly nanoclays to improve the barrier property and the antimicrobial property of the packaging materials (Sorrentino et al., 2007). Biodegradable starch-based polymers have poor moisture barrier properties due to their hydrophilic nature and inferior mechanical properties compared to plastic films. The incorporation of nanoclay particles in starch polymers has been reported to improve moisture barrier and mechanical properties (Avella et al., 2005). Therefore, the application of nanocomposites promises to expand the use of biodegradable films.

The improvement of packaging materials quality can subsequently increase food shelf life. In particular, success of packaging materials for fresh products greatly depends on the control of internal gas composition and water loss in the packaging (Sorrentino et al., 2007). In this context, the addition of silver and titanium dioxide nanoparticles in polyethylene film significantly decreased the oxygen and water vapor permeability of film and reduced kiwifruit decay and maintained their quality during postharvest storage (Hu et al., 2011). Moreover, the use of metal nanoparticles in polymeric matrices developed materials with new properties, such as active packaging for ethylene oxidation or oxygen scavenging. For example, photoactive titanium dioxide can oxidize ethylene to water and carbon dioxide, thus controlling microbial development and oxygen in the headspace (Chawengkijwanich and Hayata, 2008; Bodaghi et al., 2013; Luo et al., 2013). In addition, nano-packaging is also designed to release antimicrobials, antioxidants, enzymes, flavors and nutraceuticals compounds (Cha and Chinnan, 2004).

Nanocomposite films with antimicrobial activity could help to control growth and development of spoilage microorganisms in food. Antimicrobial packaging systems include the addition of an antimicrobial nanoparticle into the polymeric matrix, the dispersion of bioactive agents on the packaging or the deposition of an active coating on the material surface (Neethirajan and Jayas, 2011). Antimicrobial nanoparticle coatings on the polymeric matrix can reduce bacteria development on the food product put in contact with the film and can prevent any post-contamination. Metal oxide nanoparticles are the main nanoparticles used for active food packaging. Their activity can be ascribed to several mechanisms, including induction of oxidative stress, due to generation of reactive oxygen species, which may cause the degradation of the membrane structure of the cell and release of ions from the surface of nanoparticles that cause bacterial death (Emamifar et al., 2010). In particular, nanosilver (Costa et al., 2012; Mahadi et al., 2012), nanomagnesium oxide (Huang et al., 2005), nanocopper oxide (Llorens et al., 2012), nanotitanium dioxide (Bodaghi et al., 2013; Luo et al., 2013) and nanozinc oxide (Li et al., 2009; Akbar and Kumar Anal, 2014) are proposed as antimicrobial packaging. The most common nanocomposite is the silver-based system, well- known for its high stability and its strong toxicity to a wide range of microorganisms (Echegoyen and Nerin 2013).

Nanoparticles have been embedded or coated on film packaging to improve the shelf life of different food products as fruit and vegetables (Rhim, et al., 2013; Sekhon 2010) meat (Fernandez et al., 2010) and dairy products (Gammariello et al., 2011). In particular, different polymer and biopolymer films as starch, chitosan, and agar were tested to incorporated silver nanoparticles (Bi et al., 2011; Tripathi et al., 2011; Yoksan and Chirachanchai, 2010). Dairy products shelf life is influenced by both microbial and sensorial change due to the development of undesirable microorganisms. Some of them are spoilage microorganisms that may produce change in visual appearance of cheese; other ones are pathogens that affect product safety.

Pseudomonas spp. is considered a very common spoilage microbial group able to proliferate in dairy products. The most common spore-forming bacteria found in dairy products are Bacillus spp. responsible of cheese alterations and defects. E. coli O157:H7 and Listeria monocytogenes are two of the major pathogens present in unpasteurized milk and soft cheese. Moreover, yeast and mold development can also occur (Ledenbach and Marshall, 2009). To preserve the characteristics of fresh cheese during storage, techniques such as packaging under modified atmosphere, use of antimicrobial compounds and coating treatments, alone or in combination, have been suggested (Gammariello et al., 2009; Selim 2011; Di Pierro et al., 2011; Lucera et al., 2012). The application of antimicrobial compounds, such essential oil, organic acid, bacteriocins and nanoparticles, were tested to improve the shelf life of different fresh cheese (Belewu et al., 2012; Martins et al., 2010; Incoronato et al., 2011; Lucera et al., 2012).

A brief overview of some recent study on nanocomposite systems to enhance the antioxidant and antimicrobial activity of packaging to improve shelf life of dairy products is reported. Table summarizes the in vitro test of nanocomposites against the main spoilage and pathogenic microorganisms of dairy products.

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