Nanostructures for Dairy Applications

To enhance solubility and dispersion in aqueous media, reduce loss due to binding with food constituents, and increase antimicrobial efficacy by promoting contact with bacterial cell components, the antimicrobial compounds (essential oil, metal oxide, and bac- teriocin) may be structured as nanoemulsion, nanoparticles, nanoencapsulation, or nanodispersion (Sao Pedro et al., 2013; Donsi et al., 2011; Shah et al., 2013). For example, Bhawana et al. (2011) proposed a nanostructure to enhance the low aqueous solubility of curcumin, a highly potent, nontoxic, bioactive agent found in turmeric to potential application in water-based food. In particular, it was found that the aqueous dispersion of nanocurcumin was much more effective than curcumin against spoilage and pato- genic microorganisms tested (Staphylococcus aureus, B. subtilis, E. coli, P. aeruginosa, Penicillium notatum, and Aspergillus niger).

Nanoemulsions are formed when high-pressure valve homogenizers create emulsions with droplet diameters of less than 100 to 500 nm and in the droplets are incorporated antimicrobial or functional food components (McClements, 2004). A study done by Relkin et al. (2008) showed that the immobilization of a-tocopherol in oil nanoemulsion provides protection against degradation of milk fat triglycerides under high melting temperature and helps to maintain its longer shelf life. Joe et al. (2012) selected cooking oils such as sunflower, castor, coconut, groundnut, and sesame oils for development of nanoemulsion formulation. In particular, sunflower nanoemulsion showed highest activity against Salmonella typhi, followed by L. monocytogenes, and St. aureus. The selected nanoemulsion tested in vivo on different food products such as raw chicken, apple juice, milk, and mixed vegetables showed a significant reduction of bacterial and fungal populations.

Nanoencapsulation is the incorporation of vitamins, antioxidants, proteins, essential oil, and antimicrobial compounds in small vesicles or walled material with nano sizes. The nanoencapsulation offers several advantages, such as delivery vehicle for lipid soluble ingredients, protection from degradation during processing or in gastrointestinal tract, controlled site-specific release, compatibility with other food constituents, greater residence time and greater absorption (Chen et al., 2006). The nanoencapsulation of bioactive compounds, such as vitamins, antioxidants, proteins, and antimicrobial compounds may be used for the production of functional foods with enhanced functionality and microbial stability (Huang et al., 2011). For example, Makwana et al. (2014) designed an antimicrobial glass surface coated with nanoencapsulated cinnamaldehyde for active packaging of liquid foods. In particular, glass surfaces immobilized with

Table Nanocomposite Systems Tested Against Main Spoilage and Pathogenic Microorganisms of Dairy Products.




Main Results




L. monocitogenes

Lysozyme nanoparticles were tested to improving the stability and activity of antimicrobials in foods. The study revealed that the use of lysozyme-carrying immunonanoparticles is more effective than direct addition of lysozyme for inactivating L. monocytogenes in nutrient broth.

Yang et al., 2007

Loaded carbohydrate nanoparticles with nisin

L. monocitogenes

Authors showed that nanoparticles exhibit sustained antimicrobial activity against plated L. monocytogenes with efficacy that lasts several times longer than free

Bi et al., 2011


Zinc oxide and titanium dioxide nanoparticles

P aeruginosa

The efficacy of zinc oxide and titanium dioxide nanoparticles against biofilm producing P. aeruginosa was confirmed.

Vincent et al., 2014

Zinc oxide nanoparticles

P. aeruginosa

The work highlights that ZnO nanoparticles are able to inhibit P. aeruginosa biofilm formation.

Lee et al., 2014

Silver nanoparticles

E. coli and B. subtilis

Silver nanoparticles were synthesized by Salmonella typhirium. The antimicrobial assay by disc diffusion method showed that silver nanoparticles presented good antibacterial performance against tested microorganisms.

Ghorbani and Soltani 2015

Silver nanoparticles

P. aeruginosa

The antibacterial activity against Pseudomonas aeruginosa of silver nanoparticles was evaluated both in liquid and solid growth media.

It was observed that the bactericidal effect depends both on nanoparticle concentration and number of bacteria present.

Kora and Arunachalam 2011

Nanoencapsulation and nanoemulsion of Thymol, Carvacrol, Linalool and Eugenol

Molds, yeasts, coliforms, and Salmonella

Among the tested nanostructure of different essential oils, the height antimicrobial and antioxidant activity was observed for eugenol. Moreover, nanoencapsulation of eugenol can enhance the aqueous solubility and thermal stability of eugenol.

Khaled et al., 2014

Table (Continued)




Main Results


Silver nanoparticles

L. monocitogenes, E. coli O157H7, Salmonella typhimurium, Vibrio parahaemolyticus

Silver nanoparticles showed great antibacterial effects on tested foodborne pathogens. In particular, an efficient bactericidal activity was observed against E. coli O157:H7 and S. typhimurium after 6 hours of exposure time, while this time was 5 hours for V. parahaemolyticus and 7 hours for L. monocytogenes.

Zarei et al., 2014

Zinc oxide nanoparticles

L. monocitogenes

Results suggest that zinc oxide nanoparticles can be used as effective growth inhibitors against Listeria monocytogenes.

Arabi et al., 2012

Chitosan-silver nanocomposite film

E. coli, St. aureus, B. subtilis and P. aeruginosa

The authors show that chitosan as biomaterial-based nanocomposite film containing silver oxide has an excellent antibacterial ability for food-packaging applications.

Tripathi et al., 2011

Films based on chitosan and silver nanoparticles

Staphylococcus aureus, Klebsiella pneumoniae and Escherichia coli

The authors carried out a flexible film with tuned optical properties and antimicrobial activity.

Pinto et al., 2012

Nanoemulsion of orange oil

Food spoilage yeasts

The kinetics of killing curve, shown that the nanoemulsion- treated cells had lost its viability within 30 minutes of interaction.

Sugumar et al., 2015

nanoencapsulated cinnamaldehyde showed significant antibacterial activity against E. coli and B. cereus, with reductions of 2.56 log10 CFU/mL and 1.59 log10 CFU/mL, respectively, in 48 hours. Nanoencapsulation is a valuable support to enhance the antimicrobial properties of essential oils (Sao Pedro et al., 2013). In literature, in vitro and in vivo studies reported the remarkable performance of essential oils as antimicrobials against bacteria, yeasts, and filamentous fungi (Reichling et al., 2009). Gaysinsky et al. (2005) show that the nanoencapsulation of eugenol and carvacrol into nanometric surfactant micelles resulted in enhanced antimicrobial activity against E. coli O157:H7 and L. monocytogenes, as major pathogens of dairy products. However, the addition of micelle-encapsulated eugenol to milk resulted to be less or as inhibitory as un-encapsulated eugenol (Gaysinsky et al., 2007).

The antimicrobial efficacy of eugenol dispersed in nanocapsules system against model microorganisms (E. coli O157: H7 and L. monocitogenes) was also tested in vitro and in various types of milk (Shah et al., 2013). Obtained results showed that nanodispersion did not change the antimicrobial characteristics of eugenol; however, it was more effective against Gram-negative than Gram-positive bacteria. Moreover, nanodispersed eugenol did not influence the sensorial properties of milk (Shah et al., 2013). Balcao et al. (2013) tested the antimicrobial characteristics of nanoencapsulation of bovine lactoferrin for food applications. The antimicrobial activity of the nanoparticles was assessed in vitro, upon several spoilage microbial strains and pathogenic bacteria as St. aureus, Salmonella sp., E. coli, P. aeruginosa L. innocua, B. cereus and Candida albicans. Results show that lactoferrin did not exhibit any antimicrobial activity upon Gram-negative bacteria and the more sensitive microorganisms to the treatment was C. albicans.

Nanoliposomes, nanometric versions of liposomes, are vesicles consisting of one or several bilayer membranes (Mozafari et al., 2008). Liposomes are able to deliver both polar and nonpolar compounds (Dogra, et al., 2012; Mozafari et al., 2008). Nanoliposomes and liposomes have recently gained importance in the food industry for encapsulation of antimicrobials, flavor components, and enzymes (Gortzi et al., 2008). Gortzi et al. (2008) reported a 25% increase of antimicrobial and antioxidant activity of Myrtus communis extracts after encapsulation into nanoliposomes than the same extract in pure form.

da Silva-Malheiros et al. (2010) show that the utilization of nisin nanovesicle-encapsulated in combination with low temperatures appeared to be effective to control L. monocytogenes in milk. Moreover, liposomes and nanoliposomes are suggested to significantly accelerate the production of some foodstuffs, such as cheese (Mozafari et al., 2008). In particular, the addition of liposomes with enzyme are able to accelerate and improve the efficiency of cheese-ripening process and are able to prevent the development of off-flavors and to ensure the release of contents in a predictable manner (Mozafari et al., 2008).

Metallic nanoparticles with antimicrobial function are particularly effective because of the high surface-to-volume ratio and enhanced surface reactivity of the nano-sized antimicrobial agents, making them able to inactivate more microorganisms when compared to higher scale counterparts (Llorens et al., 2012). Mirhosseini and Firouzabadi (2013) highlight the ability of ZnO nanoparticles to growth suppression of E. coli and S. aureus in milk. In particular, for higher ZnO concentration (10 mM), the treatments initially reduce the total microbial population and then retard the growth. At lower ZnO concentration (5 mM), the treatment increases the lag time.

Nanofibers with diameters from 10 to 1000 nm are a platform for bacterial cultures (Qureshi et al., 2012). Nanofibers are usually not composed of food-grade substances; however, progress in the production of nanofibers from food biopolymers increases the potential application to food and dairy products (Ravichandran, 2010; Sukla 2012).

Different studies have reported the immobilization in nanostructure of biopreservatives as nisin. Nisin has numerous applications as a natural food preservative, including dairy products, canned foods, and processed cheese and is an effective antimicrobial agent against a wide range of Gram-positive and some Gram-negative bacterial strains (de Arauz et al., 2009). Nevertheless, nisin, like other antimicrobial proteins/peptides, is readily denatured by the protease enzymes, commonly acting in the acidic-rich environment of food materials. In order to overcome these problems, the loading of nisin into micro/ nanoparticles has been investigated (Colas et al., 2007; Laridi et al., 2003; Salmaso et al., 2004). To improve the physicochemical instability of nisin, Zohori et al. (2010; 2013) proposed a hybrid solution characterized by chitosan/alginate nanoparticles and nisin for biopreservation of dairy products. In particular, the antibacterial activity of nisin-loaded nanoparticles added to pasteurized and raw milks inoculated with St. aureus was tested.

Evaluation of the growth kinetic of St. aureus in the raw and pasteurized milks revealed that the nisin-loaded nanoparticles were able to inhibit more effectively microbial growth than free nisin (Zohori et al., 2010). In a consequent study, the antibacterial activity of the complex with nisin and chitosan/alginate nanoparticles against L. monocytogenes and St. aureus was tested in feta cheese. Results indicated that the nisin-loaded nanoparticles were able to control the spoilage populations, the sensory acceptance, and the physicochemical features of feta cheese (Zohori et al., 2013). Prombutara et al. (2010) proposed long-lasting antibacterial nisin-loaded in solid lipid nanoparticles as food preservatives for a diverse array of foods with different physical consistencies.

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