WOW! factor

Replacing fats in processed foods isn't easy. The presence of some fat appears to be essential for taste and texture. But fat-based fat replacements, such as Olestra, are not seen as the answer because of their laxative effect and Europe's ingredient suppliers have been left to rely on fat-mimicking carbohydrate- or protein-based replacements. But these don't always deliver either the taste or the texture that consumers want.

However, another product may soon be available to them - at least for emulsion-type products, such as mayonnaises, sauces and soups. It is known as a water-in-oil-in-water, or WOW, emulsion.

The UK's Institute of Food Research and Leatherhead International have been given £326,000 by the UK government to conduct a three-year project on the use of ceramic membranes to produce emulsions containing oil droplets in water in which part of the oil in the droplet is replaced by water.

It is a two-stage process, in which a water-in-oil emulsion is made in the conventional way using blenders or homogenisers. The resulting mixture is then gently pumped through tiny holes in a ceramic tube into a flowing stream of water to create a multiple emulsion of water-in-oil droplets suspended in water, a 'WOW'. The process is known as cross-flow emulsification, or XME. The idea is that the oil droplets will fool the mouth into believing that the mayonnaise or sauce is a regular, full fat product ? except that each oil droplet contains more water than oil.

WOW EMULSIONS TASTE AND FEEL OK

So far, WOW emulsions have been made that taste and feel OK. The aim now is to characterise these emulsions, make sure they remain stable, and then develop design rules to make WOW products.

But until WOW works, ingredients firms remain reliant on traditional fat replacement methods to satisfy demand for low fat/reduced fat products.

The number of calories that come from fat in our diet has decreased over the last two decades. Current advice is that we should be deriving 30-35% of our calories from fat. At the moment, in the UK, the figure is 38%, down from 42% in mid 1980s. But fat replacement is still a valid objective for companies formulating foods, suggests Dr Julian Stowell, science director for Danisco Sweeteners group in Redhill, UK. "Low fat foods have become very well established in a number of areas. You can hardly buy a full fat yoghurt today. But the challenge is to replace fat with something that gives the same mouthfeel and texture ? and that isn't easy."

The challenge is to design a fat blend or an oil blend which meets nutritional requirements but at the same time makes no sacrifice in performance, says Stowell. Fats have creaming characteristics ? remember your mother making a cake by creaming up the margarine with the sugar?

The fat has certain physical characteristics because of the presence of trans fats (partially hydrogenated, or partially saturated, fats). But the issue of trans and saturated fats has exploded, says Paul Wassell, senior application specialist in Danisco's UK oils and fats group in Wellingborough.

"The increasing pressure to remove trans fatty acids from food products and to remove the word 'hydrogenated' from food labels has become a global high-profile topic," he says.

In January, for example, UK retailers Asda, Boots, Co-op, Iceland, Marks & Spencer, Sainsbury, Tesco and Waitrose, announced they would ban trans fats from own-label products by end of the year.

Although trace amounts of trans fat are found naturally in dairy and meats, the vast majority are formed during the partial hydrogenation of liquid vegetable oils, such as soya, to harden them for use as shortenings and in margarines and spreads, says Wassell.

Trans fats are attractive, he says, because they can extend shelf-life and give flavour and stability. But they can also raise cholesterol and contribute to cardiovascular disease. And they are now seen as more unhealthy than the saturated animal fats they were designed to replace, Wassell adds.

However, replacing trans fats is not easy. They affect melting behaviour, oxidative stability and textural properties. Many flavours bind with fat, rather than with water. And fat can mask certain flavours that appear when the fat content is reduced. By reducing fat content, water is often added, thus affecting shelf life.

Fats in products can also help production processes run smoothly ? remove fat and you may have to adapt the production process.

Fat also affects colour as it makes food more opaque. Replace fat with water and food becomes more transparent or grey.

FOUR WAYS TO REPLACE FAT

Four methods can be used to replace fat in food, says Stowell. It can simply be removed, or either a fat-based, carbohydrate-based, or protein-based fat replacer can be used.

In the US, Danisco developed a family of fat-based fat replacers (structured triglycerides) called salatrims, based mainly on soya oil, which behaved well in foods such as confectionery and baked goods. The Danisco brand name was Benefat.

"The performance of the product is excellent. The mouthfeel and texture and behaviour in the food matrix is the same as regular fat," says Stowell. "A fat typically contributes 9 calories per gram. But these fat-based fat replacers contribute only 5 calories per gram because some of the molecule is not absorbed by the body.

"We did get novel food approval for these products in Europe but it came with so many caveats that no one has used it commercially in Europe. It would have to have a label saying it's not suitable for children, that excessive use may result in a laxative effect; and it was considered to contribute six calories per gram not five. So there has been little incentive to use it in Europe."

In the US, Proctor & Gamble also pioneered fat-based fat replacer Olestra. It came in for a lot of criticism because of its deleterious effect on the stomach and intestines: it was said to cause anal leakage. And although it is still used in the US in products such as savoury snacks and popcorn, it has not been approved for use in Europe.

So Europe is left with carbohydrate-based and protein-based fat replacers, says Stowell. Litesse is Danisco's brand name for polydextrose, a carbohydrate-based fat replacer. It is a glucose polymer structured in such a way that the body does not have the enzymes to metabolise it. It contributes a mere one calorie per gram and is fat mimetic, mimicking the properties of fat.

Protein-based fat mimetics, such as Simplesse, originally developed by Nutrasweet, are also available. Danisco has its own version, Dairy-Lo, based on whey protein from cheese. Protein-based fat replacers are slightly more difficult to use as they may degrade at high temperatures.

But WOW looks set to offer ingredients suppliers an important third way since emulsified fats and oils are present in approximately 50% of processed foods consumed in UK and account for approximately 40% of the UK's intake of dietary fat. The project partners include Arla Foods, Borregaard UK, Danisco, Degussa Texturant Systems UK, First Ten Angstroms Europe, McCormick and Puratos.

Peter Wilde, senior research scientist at the Institute of Food Research in Norwich, says WOW offers the same number of droplets, and the same size of droplets in the emulsion, but less fat. So the composition, the texture and the taste should be the same as a conventional emulsion. "The limitation with current low fat products is that you're trying to mimic the consistency by using gelling agents, thickeners, polymers. But we sense fat in a different way. People talk about fat receptors, about whether there are actual receptors in the mouth for fat molecules. It has not been proved, but the presence of fat in food gives it some sort of flavour, above and beyond the texture and physical properties of the product. With WOW, the idea is you are still sensing the oil or fat droplet, but that some of the fat in each droplet has been replaced by water.

"We are using a system where you extrude the droplets through a membrane. It is more gentle and we can keep more water droplets intact and stable. The next stage is for Leatherhead to produce these emulsions on a larger scale, ready for sensory trials to determine how much of the fat we can replace by water without having too much impact on the product."

SENSORY ANALYSIS

For the project, WOW emulsions formed by XME will be characterised and compared by sensory analysis with their conventional high fat counterparts.

Emulsions are conventionally made by whizzing up water and oil in a big blender. But the process is not particularly energy efficient - and can damage the food. It also produces emulsions containing droplets of between 0.5 microns and 5 microns in size.

The aim of XME is to produce droplets of consistent size by using a low-shear method reliant on the surface energy of the ingredients. So it is more energy efficient than conventional homogenisation methods ? a conservative estimate would be around 50% of conventional energy usage, suggests Wilde.