Nanotechnology in food

Nanotechnology

Nanotechnology consists of a great number of different processes, materials and technological applications for which the common denominator is the very small size of the material used. Due to the very small size the characteristics of the materials change – they verge on atomic characteristics. Gold is a good example of the change of the characteristics of the material. The colour and characteristics of gold we know well – yellow, with a melting point of 1200 ºC and a chemically poorly reacting metal. When we examine gold of nanoscale we discover significant changes in its characteristics. One nanometer gold particles are bluish in colour, somewhat reactive and the melting point is only 200 ºC, whereas gold particles of about 3 nanometers are red in colour and can act as chemical catalysts in the most diverse chemical/biological reactions.

Nanoparticles are very small in size; particles below 100 nm are classified as nanoparticles, even if there is no exact limit as to size when examining the biological effects of nanoparticles.

The definition is also rendered more difficult due to the different shapes of the nanoparticles – they can be ball shaped, single-wall tubular, multi-wall tubular etc. One nanometer is one billionth of a metre, or 10-9 metres and it could be illustrated thus, that the relationship between a metre and a nanometer is about the same as that of a football to the earth.

Nanomaterials in the food sector

There have always been nanoparticles in the environment (volcanoes) and most likely also in food (crystals and micelles). Nanotechnological applications only mean nanomaterials added to for example the food chain, with the aim of improving the characteristics of the products in one way or another. The following areas of application of nanomaterials can be identified in the food sector:

1. Packaging materials
2. Bioindicators
3. Ingredients in food
4. Food additives
5. Other applications in the food sector

Even though it can be said that the food applications are still at the starting point, the reasons for the enormous development of this field are easy to find. For components of nanoscale permitted for use in packaging materials and additives, a safety assessment is always required.

Packaging materials

We can use soft drink bottles as an example of packaging materials using nanotechnology; in some cases abroad a component in clay of nanoform is mixed into the plastic in order to hinder leakage of gases, such as carbon dioxide.

Bioindicators based on a colour change to silver have been developed to be added to the packaging material in order to detect when a product has gone off.

Ingredients in food

The nano development of food ingredients happens for example in the development of new nanoemulsions, where nanoscale water droplets are used. The product can be used in for example mayonnaises, cream preparations and yoghurts to reduce the fat content of the product.

Besides packaging materials, the nano-encapsulation of food additives is possibly the fastest growing area in the food sector. Using encapsulation techniques, a better absorption of e.g. vitamins and minerals is aimed for, and even the taste properties of chocolate can be enhanced by coating nanoparticles with cocoa.

The heavily increasing numbers of applications for nanotechnology in the food sector have brought up several questions related to safety and regulations. One question that occupies the safety experts is the little knowledge currently available on the possible health effects of nanoscale materials. When it comes to food, consumers are mainly concerned with safety.

According to a consumer study carried out in Germany, the safety of products containing nanotechnology should be ensured by independent authorities before nano products are taken into use on a large scale. This is the current practice, as the EU Commission requires a separate safety assessment for substances of nanoscale.

Assessment of the health effects of nanoparticles

The quality and nature of nanoparticles in food applications is varied, and it is very important to know in detail the characteristics of the nano products to be used. Food toxicology research meets a challenge here, as the characterisation of nano products is considerably more complicated than for example that of harmful chemicals that occur in food. In order to assess the health effects of nano products, for example the particle size and distribution, the level of agglomeration and aggregation, the surface area of the particle, the nature of the surface material and the related chemistry have to be known. Part or all of these characteristics can still change in the food and/or in the digestive tract. The analysis of nanoparticles or nano products in food and feed constitutes its own challenge. Ordinary equipment used for chemical analysis is not really suited for the task, and special equipment is needed.

Food toxicology of nanoparticles

There is not yet unanimity in the scientific community as to which of the characteristics of nanoparticles are critical for the determination of the possible toxicity of a nano product. It is however considered likely that reliable assessments can not be carried out when determining the so-called dose-response relationship using only the mass of the nano product.

The World Health Organisation WHO and the Food and Agriculture Organisation, both UN organisations, determine food-borne exposure to be an event when the chemical, biological and physical exposure substances that have entered the body are assessed either qualitatively and/or quantitatively. This definition is also suited to nanoparticles, which do not differ from ordinary chemicals in this regard.

The characteristics of nanoparticles can be similar to the corresponding ones that are not nanoscale, which means that ordinary testing can be used in assessments of harmfulness. It can also be otherwise. In these cases, the toxicology differs clearly, due to the very small scale, from corresponding products that are not on nanoscale.

Movement of nanoparticles

The absorption of nanoparticles from the intestine is a complicated phenomenon, which starts from the absorption of the particles into the mucous membrane of the intestine and several different stages following that. At this point in time it seems likely that the absorption and transfer would have a connection with the size and charge of the particles – anionic particles penetrate the mucous, but the cationic particles remain in the mucous and can not make it all the way to the epithelial cells. The mucous can therefore be considered to be the body’s first protective wall, by which the nanoparticles are hindered from entering the body. The epithelial cells of the gastrointestinal tract form the next level of defence of the body. Exuding from the spaces between the cells, the particles can enter the body by way of the so-called paracellular route which is rare in a healthy intestine.

Another route by which the particles move into the body is via the normal nutritional intake of the intestine, that is to say the transcellular route. Nanoparticles have been shown to move efficiently into the body, but e.g. the size and surface structure of the nanoparticles have a great impact on their absorption.

When the particles have cleared their route through the first obstacles and have moved into the bloodstream they can react with components in the blood, such as proteins. This factor can be important for the spread of the particles, as it has been discovered in work with laboratory animals that the smallest particles spread to all parts of the body and nanoparticles have been located in all of the internal organs of exposed laboratory animals. The ability of the natural barriers of the body, such as the blood-brain barrier, placental barrier, blood-milk barrier and blood-testicle barrier, to hinder nanoparticles is unclear at this stage.

Toxicological risk assessment

Nanoparticles have new characteristics, which are related to the small size, physiochemical characteristics, chemical structure and the structural activity of the surface components. These characteristics are used in nanotechnological applications, but at the same time it is these characteristics that are important for the assessment of the health effects.

For additional information:
Professor Kimmo Peltonen, Chemistry and Toxicology Research Unit, Evira
tel. 02077 24410, kimmo.peltonen evira.fi

Evira.fi

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