Source: New Scientist

 NOTHING says summer holidays quite like ice cream. On a hot afternoon by the sea, there's little to beat the simple pleasure of a cooling scoop of your favourite flavour. Can food get much more satisfying than this?

Vic Morris thinks it can, with the help of nanotechnology. He is part of a team tweaking foods to trick the body into feeling pleasantly full long after the final mouthful - and without overeating.

Ice cream that makes you feel full could be just the beginning. Nanotechnology promises even saltier-tasting salt, less fattening fat, and to boost the nutritional value of everyday products. Nanofood supplements could even tackle global malnutrition.

So what is a nanofood? It isn't just about nanoparticles. Many foods have a natural nanostructure - the proteins in milk form nanoscale clusters, for example - that can be altered on the nanoscale to enhance their properties.

In fact, researchers have been changing the nanostructure of food for years, for example by adding emulsifiers to improve the texture of ice cream. It's the emergence of technologies such as atomic force microscopy that has changed the game by finally opening a window on the nanoworld. Rather than working blind, Morris can now take a close look at the tiny structures he works on, understand their behaviour and then make changes in a more rational and deliberate way.

These imaging techniques are behind the high-satisfaction foods Morris is helping to develop at the Institute of Food Research (IFR) in Norwich, UK, which promise to help fight obesity by making people feel full before they overeat. Many foods, from ice cream to hollandaise sauce, contain emulsions, in which the fat is whipped into tiny droplets coated with a stabilising layer of proteins. Emulsions were always assumed to collapse in the stomach, but Morris has seen otherwise: some don't break down until their protein coat is disrupted by the bile salts they meet in the small intestine.

By cross-linking the proteins, the IFR team can strengthen the protein coat and delay the emulsion's breakdown until the final part of the small intestine, called the ileum. The sudden burst of fats so far down the small intestine triggers the "ileal brake" - the mechanism that makes us feel full. "The body thinks it has a high-fat diet," says Morris. The team is now looking to apply this approach to real foods.

Hitting the ileal brake isn't the only way emulsions could be co-opted into helping cut our fat intake. In "diet" versions of many emulsion-based foods, such as mayonnaise, about half of the fat content is replaced with water, making them less satisfyingly creamy. One alternative is to hide that extra water as nano-droplets within each drop of oil so that the mouth experiences less water and more creamy fat. If the idea works as well on the production line as it does in the lab, low-fat mayonnaise might taste and feel exactly like the regular version.

The encapsulation idea has caught the eye of the food industry. "It's about improving the nutritional value and shelf life of food products without affecting anything else, such as taste or texture," says Charles-François Gaudefroy, an R&D director at Unilever, which owns numerous food brands.

The food industry is notoriously tight-lipped about products in development (see "Ready for nanofoods?"), and Gaudefroy won't say what nanofoods Unilever is looking into. Two other food multinationals, Kraft and Nestlé, declined to talk about their research in the area at all. One area they are likely to be working on, however, is finding ways to add extra nutrients to their products by packaging them inside fat or polymer particles.

"We know that the food industry is looking at encapsulating certain ingredients like omega-3 fatty acids, vitamins or minerals," says Frans Kampers, who researches bionanotechnologies at Wageningen University and Research Centre in the Netherlands. The idea is an attractive one. Oil-soluble nutrients can be poorly absorbed in the watery environment of the gut, with a proportion passing right through the body. Nano-encapsulation converts them to a dispersed form that is more easily taken up (Current Opinion in Colloid & Interface Science, vol 14, p 3). Wrapping them in nano packages also extends their shelf life, masks any unpleasant tastes and, in the case of nano-emulsions, makes them invisible to the naked eye so that they don't affect a food's appearance.

The food industry is looking at encapsulating vitamins, minerals and omega-3 fatty acids
However, translating these benefits into practical products is proving difficult. Stabilising nano-emulsions is notoriously hard - as is demonstrating any health benefits. "Three or four years ago there was a lot of hype about nano," says Gaudefroy. Many projects were started on the back of that hype, but quite a few have failed because of the difficulty of delivering something with tangible advantages, he says.

While Unilever, Kraft and Nestlé say they have no nano-enhanced foods on the market, smaller companies are already selling nanofoods over the internet. In the US, RBC Life Sciences, based in Irving, Texas, markets Slim Shake, a "meal-replacement shake". The company does not reveal any technical information about the product, but Kimberly Lloyd of RBC told the BBC in October 2008 that it is taking "4 to 6-nanometre individual silica particles and... coating them with chocolate and cocoa ingredients". The idea is that the increased surface area should deliver more of a flavour hit to the taste buds. The company claims this means less fat and sugar can be used, cutting the calorie count.

It isn't the only such product available. Nanosilver, for example, is available in various health supplements and bottled waters, and its suppliers suggest it can boost the immune system. In November 2008, the European Food Safety Authority rejected a request to approve nanosilver products for sale in the European Union, because of a lack of safety data. It is "persistent" nanoparticles like silver and silica, which don't break down in the body, that are causing the greatest safety concerns among food researchers, says Morris.

Micrometre-sized persistent particles of silica and titanium dioxide have been used as food additives for decades, for example as whiteners in products like chewing gum, with no apparent ill effects. Make the particles smaller, and things are different: some nanoparticles seem able to penetrate the cells lining the gut, and so have the potential to travel around the body. Last December, a team led by Roel Schins at the Environmental Health Research Institute (IUF) in Düsseldorf, Germany, published research suggesting that some nanoparticles, including silica and titanium dioxide, can induce DNA damage in human intestinal cells (Nanotoxicology, vol 3, p 355).

However, other work hints that the body might not be entirely defenceless. In the 1980s, Jonathan Powell, now at the MRC Collaborative Centre for Human Nutrition Research in Cambridge, UK, was part of a team which showed how the gut uses lymphoid structures called Peyer's patches to mop up persistent titanium dioxide and silicate microparticles. They also estimated that everyone in the UK ingests about 40 milligrams of dietary inorganic particles per day. "As far as we can tell, these food additives aren't doing much," he says.

Powell suspects that nanoparticles have always formed naturally in the gut and been scavenged by the Peyer's patches, which are part of the immune system (Journal of Autoimmunity, vol 34, p 226). "I think that food additives are riding this route, hijacking the mechanism," says Powell.

While questions over the safety of persistent nanoparticles still linger, other food nanoparticles are essential for our health. Much of the iron in both meat and plant-based foods is in the form of ferritin, a storage protein which forms particles with a diameter of 12 nanometres and an iron oxide core. The human gut has been exposed to these dietary nanoparticles for millennia.

Bottom up

Dora Pereira, one of Powell's colleagues in Cambridge, is working on a project that aims to boost our iron intake by mimicking ferritin. Over 30 per cent of the world's population suffers from anaemia, mostly due to iron deficiency, and today's iron supplements aren't particularly effective. "Current supplements are so different to what we are normally exposed to in our diet that they result in side effects, or are poorly absorbed," says Pereira.

To tackle the problem, the team has made nanoparticulate mimics of ferritin by wrapping iron oxide in a coat made from compounds found naturally in food, such as tartaric acid. Tests on iron-deficient volunteers look promising, says Pereira: the nano-iron was absorbed well and caused fewer side effects than standard supplements.

The benefits of the nanofoods glimpsed so far could be just the beginning. Rather than processing ingredients to create beneficial nanoscale components, a far more flexible approach would be to build foods almost from scratch. A team at the Wageningen University and Research Centre has already created a meat-like structure built up from milk protein to demonstrate how this could one day be done (Biomacromolecules, vol 8, p 1271).

While the researchers used a food extract as their starting point, in principle it might one day be possible to synthesise the building blocks of food at the nanoscale and assemble them to make artificial foods. Kampers thinks such an approach could ultimately provide a way to help feed the world's rapidly expanding population. "It is impossible to produce the amount of meat needed and we need to find an alternative high-protein route."In the shorter term, the benefits of new iron supplements are clear to see, and many will be lured by the promise of a truly satisfying low-fat meal. Feel-full ice cream could soon be on sale at a beach near you.

Editorial: How to persuade us to swallow nanofood

Ready for nanofoods?
What might be the first nano-enhanced food to hit supermarket shelves? The food industry remains tight-lipped, and inquisitive consumers might not discover which products are in development until they are actually launched.

In the UK, the food industry recently came under fire from the House of Lords Science and Technology Committee for its lack of transparency. "The food industry did not wish to publicise their work on developing nanotechnology-based products, either here or in the US," says Lord Krebs, chairman of the inquiry into nanotechnologies and food. The committee suggested that food companies are fearful of a consumer rejection of nanotechnology on the same scale as that which affected genetically modified (GM) crops.

Charles-François Gaudefroy of Unilever says they recognise the issues surrounding nanotechnology must be debated in public. "We don't want to be in the position of the GM industry, especially because our products are put on the market for consumers. We are interested in nano but we must make sure that our products are seen with trust and confidence by consumers."

Trust and confidence depend on whether new products can be shown to be safe. "Of course foods have to be safe. For the food industry, safety is a given," says Ian Norton, formerly at Unilever Research, and now at the University of Birmingham, UK. Lord Krebs, a former head of the UK government's Food Standards Agency, is more cautious: "When I was head of the FSA, there were plenty of cases where the food industry's claims about safety were not borne out."

The taste of tiny
Nanoparticles are usually defined as having one or more dimensions of the order of 100 nanometres. But nano isn't always best: in many cases, particles don't have to be that small.

A few years ago, a group of researchers set out to make nano-salt. The smaller the particles, the higher the ratio of the salt's surface area to its mass, and the team reasoned that this would allow them to use less salt to achieve the same taste. The team tested a variety of nano-sized salt particles, but the product that eventually emerged - called Soda-Lo, and sold by Eminate, a spin-out company of the University of Nottingham, UK - has micrometre-sized grains, 50 to 100 times larger than the largest nanoparticles. Particles this size turned out to give the best taste hit, says Kathy Groves of Leatherhead Foods International, who worked on the project. "The saltier salt is the micro salt."

Nanoparticles can have some advantages over their larger cousins, but they also have drawbacks, Groves adds. "A lot of nanoparticles are very sticky and tend to clump together."