Worth its salt?

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Related tags: Salt, Taste, Sodium, Flavor

Is the holy grail of salt replacement now finally within reach? Michelle Knott talks to the companies at the cutting edge of research to find out

Salt reduction is big business and it is only going to get bigger as the health and wellness juggernaut continues to pull legislators, consumers and the food industry along in its wake. Companies are already marketing extremely promising flavour enhancers designed to reduce sodium levels without impacting on taste and other functional properties. But there is also more basic research going on into our perception of saltiness, and that research is starting to yield exciting results.

In February, US company Senomyx announced that it has identified the individual protein responsible for salt perception in the taste buds. This should enable it to develop screening assays that can track down potential salt substitutes and saltiness enhancers from its library of over 1.5M compounds.

San Diego-based Senomyx already has a strong track record in this area and counts some of the world's biggest food companies among its partners. For example, its unique approach has tracked down the savoury receptor and Nestlé is already marketing food products using compounds identified using Senomyx's assay-based technique.

After identifying the sweet receptor, the company has also uncovered a sucralose enhancer that should enable manufacturers to reduce the level of sweetener by 75%, and a sucrose enhancer that promises a 40% reduction in sugar. Senomyx has also developed a bitter blocker and has recently started work on cool taste enhancers.

But the salt receptor proved elusive until this year, when the firm's systematic search finally tracked it down. "We started from scratch," says chief scientific officer Mark Zoller. "We went through all the proteins in a taste bud and we know there are about 15,000 of them. We then developed a set of criteria that a protein would have to meet to be a salt taste receptor."

First, the protein should be present in taste buds and not elsewhere on the tongue. Second, it should be on a unique type of cell, not on the sweet, savoury, bitter or sour sensing cells in the taste bud. Third, it should react with sodium in some way. This might be by binding it to one or more sites on the protein, as the sweet, savoury and bitter receptors do.

Alternatively, it might be an ion channel that enables sodium ions to pass through the cell wall, like the sour receptor. "We have now identified one protein that meets all the criteria and we've called it SNMX-29," says Zoller. "However, we're not going to give away details of what kind of protein it is yet."

The next step is to develop a screening assay using the protein. It's like building an array of taste buds that can only taste saltiness. These assays can screen many samples at a time, enabling Senomyx to hone in rapidly on any compounds that affect SNMX-29. Zoller is reluctant to put a timescale on the project, but he is confident that this systematic approach will yield results. "Each project is different but for each of the receptors we're working with we've been successful at finding compounds with a taste effect. There's nothing hit and miss about our approach."

Of course, Senomyx is not the only game in town and there is other research that looks likely to yield results within a shorter timeframe. A number of projects have achieved promising results by manipulating the structure of salt itself, rather than looking for alternative compounds.

Eminate is an industry-facing partner of Nottingham University and a centre of excellence in nanotechnology, specialising in food. The company's research into nanosalt could yield commercial food products within the year, according to technical director Dr Stephen Minter.

The idea of using nano-sized salt crystals is to increase the surface area and get a faster blast of saltiness. But there's a problem. "Nanosalt is fine in theory but when you make it it's far more hygroscopic than normal salt, so it becomes a cake within a few minutes and is completely impractical for use in the food industry," says Minter. "We've developed a free-flowing microsalt." The production process is proprietary, but Eminate can reveal that it involves spray drying. "We end up with salt that looks like a football made up of microcrystals. It's the production of this ball that makes it free-flowing," he says.

The hollow balls are between five and 50 microns in diameter and are made up of sub-micron crystals. In contrast, normal salt has a crystal size of between 150 and 200 microns. "The balls work anywhere where people apply salt to surfaces, as well as in baking. The hope is to get it into crisps and snacks and a 50% reduction is what we're working towards," says Minter.

The indications are that Eminate's microsalt preserves the other functional properties of salt, and samples are now available for companies to test. "We're hoping to have products in the shops this year," adds Minter.

Amorphous mass

Leatherhead Food International (LFI) has also been looking at novel structures that could boost saltiness. Its work on non-crystalline, amorphous salt attracted industry support from around 30 companies, including ingredients suppliers, manufacturers and retailers.

"Amorphous salt is like a sugar glass structure," says Stuart Clegg, principle scientist in the ingredients and food innovation section at LFI. "You could think of it as a solution with the water removed. The idea is that if you don't have to break up the crystalline structure it dissolves more easily for a more intense initial hit."

One drawback of the research is that LFI's instrumentation is not powerful enough to see for sure whether the researchers have produced amorphous salt, as opposed to very small crystals. Nevertheless, the initial results are encouraging.

"When we assess the sensory impact we find a sharper initial intensity - a very sharp initial saltiness," says Clegg. "But we've been looking at time-dependency too. The time-intensity curve for the amorphous salt has a sharper peak that disappears faster, but now the question is: how does that relate to the overall sensory experience?"

If the length of the saltiness hit proves to be an issue, one solution would be to mix the amorphous salt with larger crystals to prolong the salty effect. "We looked at removing 10, 20 and 30% to see how far we could go, but I think a 20% reduction in salt is a sensible goal." Clegg also points out an important limitation of this work. "This technology is only applicable where salt is used as a solid. For example, in bread it would be present in solution so it wouldn't help, but it might be present as a solid in some baked products."

Blue sky research holds promise for the future, but consumers want reduced salt products today and companies are already producing workable salt-reducing products. For example, Armor Proteines has attracted a great deal of attention for Lactosalt Optitaste. This milk-based mineral blend replaces between 25 and 40% of salt in products like bread, meat and cheese.

"Most salt replacers are flavour-based so they're great for taste but useless for technological benefits," says marketing manager Beno&icirct Laplaize. "Others are 'chemical salt-based' so they're great for technological benefits but in general not good for taste and not good for labelling. Lactosalt brings both benefits, plus a friendly label." According to Laplaize, a variety of food companies are currently developing products using the new substitute.

Another recent arrival was the Maxarite range from DSM. This yeast-based flavour enhancer system aims particularly at dairy and baked products and targets a 30 to 50% reduction in salt. "When certain substances are in food, Maxarite can increase their effectiveness, so if there is some salt present it boosts the perception in the mouth. It's a unique mechanism," says business manager Hanneke Vedhuis.

The range includes Maxarite Delite and two salt blends - BSalt and DSalt - which are aimed at bakery and dairy, respectively. The salt blends include potassium chloride, which normally tastes bitter, but DSM claims that the other ingredients in Maxarite effectively mask any bitterness.

There are already bakery products on the market that are using Maxarite, and advanced trials are underway in the dairy sector. "You can't develop a new cheese in six months," says Veldhuis.

So there's lots going on, but the pressure to drive down salt consumption is growing. While it presents technical challenges, it also presents a huge marketing opportunity for ingredient suppliers and manufacturers. With so much at stake, it seems certain that the number of innovations can only increase in future, so watch this space!

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