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Nanotechnology in the food industry

Craig Duckham FIFST reviews the impact of nanotechnology on the food industry and identifies current and future application areas.

Introduction
The term nanotechnology generally refers to the manipulation, development and manufacture of materials in the size range 1-100 nm. At this size, particles can exhibit properties not necessarily observed in larger particles, including colour, melting point, crystal structure, reactivity, conductivity, magnetism and mechanical strength. They have large specific surface areas and may demonstrate quantum effects rendering their behaviour difficult to predict. They are extremely mobile in their free state with a low sedimentation rate. Nanomaterials(NMs) may be widely occurring, natural or specifically engineered (ENMs).

 PubMed) (2014 data extrapolatedAs a measure of the growing interest in nanotechnology, the number of publications on its use has soared in the last 10 years, with less than a hundred papersciting nanoparticles in 1994 rising to over 18,000 manuscripts by the end of 2014 (Figure 1).

There is a wide range of potential applications where nanotechnology could provide innovative solutions for the food and beverage industry [1]. The key areas are illustrated in Figure 2.

Food applications for nanoparticles and nanoemulsions
Nanoparticles were initially investigated for applications in medicine, primarily for use in enhanced drug delivery, improving bioavailability and in formulating poorly soluble or poorly absorbed active ingredients.The lessons learnt from the pharmaceutical industry will be readily translated into benefits for the food industry, where improvements in formulation and in the bioavailability of functional ingredients can be expected.

Spray drying is a common way of generating dry powders of encapsulated ingredients and theparticle sizes obtained can be as low as 2 micron at laboratory scale or around 20-50 micron at production scale. Current laboratory scale spray driers can produce powders with a particle
size ranging from around 300 nm to 5 micron. Typically nanoemulsions or dispersions of functional ingredients prepared with surfactants, lipids, gums or carbohydrates, are sprayed in air or nitrogen into a large cylindroconical vessel where the water (or other solvent) evaporates and the resulting fine powder is collected in a cyclonic chamber. The main areas where nanotechnology may have an early impact in the food and beverage or agri-food industries

Microemulsions, nanoemulsions and nanodispersions of particles of around 100 nm can remain stable for longer than conventional suspensions and can form clear pseudo-solutions. This can be of particular value if there is a requirement to reduce the amount of sugar, surfactant or ethanol in a formulation. Micelle carrier systems have been developed by a number of companies to take advantage of this property. For example, a polysorbate micelle carrier technology has been patented which solubilises a range of poorly soluble ingredients for incorporation into clear beverages [2]. It has been used to improve the stability of orange oil to enhance antioxidant activity, combining both water and fat soluble antioxidants within one matrix.

Milk comprises an emulsion of small fat droplets and a suspension of milk proteins, such as casein and whey. Casein particles (in the form of micelles) less than 100 nm in diameter are present at a higherproportion in skimmed milk than in full fat milk. The size, conformation, and shape of casein micelleshave recently been revealed using asymmetrical flow field-flow fractionation and multi-angle light scattering techniques [3]. The majority are present as spherical bodies with some forming elongated aggregates.

Nanocomposites in food packaging
The use of nanofibres, tubes or particles as fillers to reinforce biopolymer packaging materials creates nanocomposites. The small size and increased surface area of the nanoparticle fillers enhances their interaction with the packaging matrix improving its performance and extending the potential use of biopolymers, which are more readily degradablein the environment than plastics. Improved strength and flexibility can be achieved and the incorporation of antimicrobials can extend the shelf life, reduce wastage and improve food safety.

Figure 3
Figure 3: The use of intercalated clay or the inclusion of nanofibres within the walls of otherwise porous plastic bottles imparts barrier properties by forcing oxygen or other gaseous molecules along a tortuous route of diffusion.

Incorporation of inert nanomaterials, such as clay, into plastics, such as PET, can improve the barrier properties. This is achieved by presenting oxygen molecules diffusing across the walls of a plastic beverage bottle with discrete barriers to negotiate forcing them to take diversions and slowing their progress, hence reducing the rate of oxidation of the bottle contents (Figure 3). The inclusion of nanoclayparticles at levels of 5% or less can cut oxygen diffusion by 75% and block UV transmission whilst maintaining transparency and strength. SABMiller and Trinity College Dublin are incorporating nano-sheets of boron nitride into plastic bottles to reduce losses of CO2 from carbonated beverages and prevent the inward diffusion of oxygen. Their aim is to improve the shelf life of beer in plastic bottles.

Food processing applications
In the water treatment industry nanostructured materials offer a range of opportunities [4]. A number of proposed filtration systems rely on microporous materials including claybased ceramic plates that can be rendered antimicrobial by incorporating colloidal or nanoparticulate silver. Nanoporous filters for supply or point of use water purification have been developed for the removal of bacteria and heavy metals and offer an alternative to reverse osmosis. Nano fibre based filtration systems, mesoporous clays and ceramics coated with a monolayer of selective absorbents have all been developed to provide contaminant free drinking water.

The increased surface area of nanostructured materials enhances the surface reactivity potential of catalysts, increases the rate of chemical reactions and can improve the absorptive capacity of materials. In water treatment applications, titanium dioxide (TiO2) can function as both a photocatalytic reducing agent  and an adsorbent. Nanoscale TiO2 photocatalysts are more effective at producing free radicals in the presence of water, oxygen and UV radiation than equivalent microparticulate TiO2. The aim is for the highly reactive radicals to decompose organic contaminants into less toxic constituents. Nanoscale zero-valent iron, either in a slurry or impregnated into membranes, offers a means to agglomerate heavy metal ions and break down chlorination by-products, which is potentially useful for the decontamination of groundwater.

Surface modified materials with anti-microbial properties are also under development. One approach is to engineer surfaces with immobilised enzymes that either degrade key components of biofilms or are toxic to the fouling organisms.

Zeolites are microporous aluminosilicate solids that can act as molecular sieves creating sizeselective absorbents; they present a large surface area for chemical reactions in catalysis applications. They form from natural sources, such as volcanic ash, or, when high purity is required, they can be synthesised from silicon-aluminum solutions or from coal fly ash.

A Dutch nano-engineering company, Aquamarijn Micro Filtration, produces ceramic microsieves, with nanopores from 100 nm in diameter, which act as filters for a variety of applications. In the UK Micropore Technologies uses micro-engineered membranes to produce mono-dispersed emulsions and liposomes of a range of materials across many application areas.

Nanoencapsulation of food ingredients
 Widely available cyclodextrins represented as simplified molecular structures.Cyclodextrins have been successfully used to encapsulate a wide range of fat soluble functional ingredients by forming molecular inclusion complexes. Cyclodextrins are a form of modified starch with a ring structure made up of glucose units. The most common types in routine use comprise 6, 7 or 8 member rings and are termed alpha- beta- and gammacyclodextrins (gamma cyclodextrin is shown in Figure 4). They have a small outer diameter of less than 2 nm and a polar outer surface allowing them to dissolve in water. Their inner core forms a non-polar cavity which can contain small lipophilic molecules, such as food flavours, fat soluble vitamins and natural colours e.g. carotenoids. This structure enables cyclodextrins to be used to improve the dissolution properties of ingredients with poor water solubility.

Cyclodextrins have been used for many years to stabilise flavours, off-flavours and taints. A single shot of powder of a complexed flavour can be easily diluted in an appropriate quantity of product and used for training purposes. Sensory panels can be trained to recognise positive and negative attributes and assess flavour level. This systematic approach can lead to improved quality management and process control [5]. Principally used in the brewing industry, these products are also being adopted across the food, beverage and water industries. Cyclodextrins have also been investigated for improving the stability of bitter tasting products containing compounds, such as flavonols (e.g. quercetin and myricetin) [6]. Wacker has reported the use of cyclodextrins for taste masking of ginseng and green tea [7].

Food grade amorphous silica nanoparticles have also been used to encapsulate flavours. For example, tetraethyl orthosilicate can be hydrolysed with flavour retained on gelation [8]. Modified retention and release profiles can be achieved. Flavour retention was more efficient for relatively polar molecules, such as alcohols, compared to non-polar molecules, such as monoterpenes [9]. Nanoparticulate flavour formulations using silica with chitosan have recently been patented in China [10].

An insight into the growing use of nanotechnology in everyday products can be gained from a publicly available online database of over 1,600 nanotechnologybased consumer products [11]. The database was set up by the Project on Emerging Nanotechnologies (PEN) developed by The Wilson Centre and Virginia Tech in the USA to gather data from the supply chain and is compiled through voluntary submissions from industry. Currently, 96 products on the PEN database reference the white pigment powder TiO2 (E171), widely used in confectionary products and as a free flow agent in seasonings and flavourings. CoQ-10 products, typically formulated with micellar technologies or cyclodextrins, are one of the most common nanoproducts in the supplements sector.

Cellular phospholipids form the familiar membrane bilayer sheets. In isolation they are amphiphilic and can be utilised as surfactants. For example, lecithin phosphatidylcholine from serum albumen can form bilayer based spheres termed liposomes, when subject to sonication; they are commonly used in cosmetics. The PEN database includes a liposome based vitamin C supplement.

Proteins also have amphiphilic properties and can be utilised in an analogous way to form stable micelles. Casein micelles are being investigated for their ability to carry functional ingredients for use in clear beverages and sports drinks [12]. Stable micelles with fat soluble ingredients and a particle size distribution between 50-400 nm can be formed using plant saponins from Quillaja. They have recently been developed for use in clear beverages [13].

Food Safety
Portable testing systems for the rapid detection of biological and chemical contaminants are emerging. The Dutch company, Nanosens, has developed a proprietary technology based on platinum, gold and palladium
nanowire based chips.

Semiconductor based silicon nanowires (SiNWs) doped with boron and other elements have been used for the detection of proteins and antibodies in real time. They are small and sensitive and could be used in sensors to detect a wide range of analytes including pathogens, toxins and biological agents in water, air and food. A carbon dioxide sensor based on polyaniline boronic acid conductive polymer nanoparticles has been developed for applications including monitoring grain spoilage.

Nanotechnology may also be of benefit to the food industry in anti-counterfeit technologies, for example the inclusion of covert tags on labels. Tamper evident features of packaging, colour shifting security inks and films and covert features such as miniaturised text are all strategies that could be enhanced by the adoption of nanotechnology. The use of novel thermochromic or photochromic inks could be adopted for marketing, brand protection or product safety, where they could be used to indicate exposure to extremes of heat or light.

Regulation
Although not yet adopted for the food industry, EU regulations were introduced in 2009 to cover the use of nanomaterials in cosmetics: ‘Colorants, preservatives and UV-filters, including those that are nanomaterials, must be explicitly authorised. Products containing other nanomaterials not otherwise restricted by the Cosmetics Regulation will be the object of a full safety assessment at the EU level, if the Commission has concerns. Nanomaterials must be labelled in the list of ingredients with the word ‘nano’ in brackets following the name of the substance, e.g. ‘titanium dioxide (nano)”.

The European Commission now requires notifying of any such products containing nanomaterials six months before they are placed on the market. A dedicated web portal is available to facilitate this. It is reasonable to assume that similar legislation will be rolled out for food and beverages in the near future. However, currently only the presence of ENMs appears to be under consideration for controls. An ENM, according to EU regulation No 1363/2013 published on 12 December 2013, is defined as ‘…any intentionally manufactured material, containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm to 100 nm.’

The US Food and Drug Administration (FDA) issued guidance for industry on manufacturing process changes in June 2014 [14]. This publication identified factors to be considered when a change in process may affect a food substance already on the market. This would include the development and use of nano forms of food ingredients which could encompass flavour emulsions, suspensions, powders and encapsulation coating materials or carriers. Consideration should be given to factors that:
i. Affect the identity of the food substance
ii. Affect the safety of the use of the food substance
iii. Affect the regulatory status of the use of the food substance
iv. Warrant a regulatory submission to FDA.
For materials utilising nanotechnology that are already on the market, manufacturers should consult with the FDA to obtain an opinion on their use. The FDA has published an updated fact sheet on nanotechnology to guide developers and manufacturers through its current position [15].

Analysis
Characterising and monitoring nanoparticles, nanotubes and fibres in powders or dispersions in liquids, presents a number of technical challenges. There are now tools available for routinely measuring particle numbers, diameter, size distribution, shape and charge characteristics (zeta potential) using a variety of technologies including particle tracking systems to improve the quality of particle characterisation. Currently the characterisation of the very smallest particles or droplets in the 1-10 nm range and nanostructured materials within a matrix requires advanced microscopy techniques, such as atomic force microscopy (AFM), field emission-scanning electron microscopy (FE-SEM) and cryogenictransmission electron microscopy (cryo-TEM) [16]. New research is opening fresh horizons for particle characterisation. Hong-Gang Liao and co-workers at the Lawrence Berkeley National Laboratory in the USA are using an advanced direct detection camera and TEM to study the growth of platinum nanocrystals and are challenging the established theories of crystal growth [17]. The team is extending its work into other materials; this appears to be a ground breaking innovation relevant to the fields where crystal shape and crystal development have an impact on product properties.

The Future
The use of nanotechnology in the food, beverage and allied sectors is in its infancy but there are clearly many opportunities to innovate and investigate new ways of working with these materials. The tools are becoming available to enable us to learn from the nano-scale processes that are operating in our everyday environment. The next ten years will bring further understanding of the surface chemistry of very small particles, foam and emulsion stability, the migration of particulates into food and water, the barrier properties of packaging, the development of thermochromic and photochromic materials as indicators of product shelf life and storage conditions and many more new applications for nanotechnology in the food sector.

Craig Duckham, PhD MSB FIFST, runs CD R&D Consultancy Services
Tel: +44 (0)1372 377352
Email: Craig.Duckham@CDRnD.co.uk
Website: http://www.CDRnD.co.uk
LinkedIn: http://uk.linkedin.com/in/scduckham
Twitter: @CDRnD

References

1. Simpson, W.J. and Hughes, P.S. (1995). Applications of cyclodextrins in brewing technology (1995). In: Proceedings of 25th International Congress of  the European Brewery Convention, 1995. 25, pp. 523-532.

2. Lucas-Abellán, C., Fortea, I., Gabaldón, J.A., and Núñez-Delicado, E. (2008). Encapsulation of quercetin and myricetin in cyclodextrins at acidic pH. J. Agric. Food. Chem. , 56, (1) pp. 255-9.

3. http://bit.ly/1acC16q

4. Ciriminna, R. and Pagliaro, M. (2013). Sol–gel microencapsulation of odorants and flavors: opening the route to sustainable fragrances and aromas. Chem. Soc. Rev., 42, pp. 9243-9250.

5. Vieth, S.R. (2004). Retention, diffusion and release of flavor molecules from porous silica sol-gel-made particles. Doctoral thesis. Swiss Federal Institute of Technology Zurich, Switzerland. 188 p.

6. International patent WO2013004003

7. http://www.nanotechproject.org/cpi/

8. International patent WO2007122613

9. Yang, Y., Leser, M.E., Sher, A.A., McClements, D.J. (2013) Formation and stability of emulsion using a natural small molecule surfactant Quillajasaponin. Food Hydrocolloids 30, 589-596.

10. http://www.regulations.gov/contentStreamer?objectId=09000064817725ec&dis...

11. http://www.fda.gov/scienceresearch/specialtopics/nanotechnology/ucm40223...

12. Domingos, R.F., Baalousha, M.A., Ju-Nam, Y.M., Reid, M., Tufenkji N., Lead, J.R., Leppard, G.G. and Wilkinson, K.J. (2009). Characterizing manufactured nanoparticles in the environment: multimethod determination of particle sizes. Environmental Science and Technology,43, pp. 7277-7284.

13. Liao H-G, Zherebetskyy, D., Xin, H., Czarnik, C., Ercius, P., Elmlund, H., Pan, M., Wang, L-W. and Zheng, H. (2014). Facet development during platinum nanocube growth. Science, 345, (6199) pp.916-919.

Further Reading

IFST Information Statement on Nanotechnology published by the Institute of Science and Technology (December 2013).

Meridian Institute’s Global Dialogue on Nanotechnology and the Poor: Opportunities and Risks(GDNP) 2006. Thembela Hillie, Mohan Munasinghe, Mbhuti Hlope, Yvani Deraniyagala (Eds).

Nanotechnology in the Food, Beverage and Nutraceutical Industries (2012). Q. Huang (Ed) Woodhead Publishing, Ltd. 474 p.

The Royal Society and Royal Academy of Engineering Report on Nanoscience and Nanotechnologies: Opportunities and Uncertainties (July 2004).

 



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