The future is bright

In broad terms, a useful rule of thumb is 'like dissolves like'. In other words, materials are most likely to be soluble in other materials that are similar, particularly in terms of a property called polarity.

Oils and fats tend to be non-polar whereas water and alcohols are described as polar.

The 'like dissolves like' rule means that polar materials dissolve in other polar materials, but not in non-polar materials. For example, oils tend not to dissolve in water.

Unfortunately, the choice of materials available to the formulator, and the requirements of the product, mean that the 'like dissolves like' rule cannot always be conveniently applied, and lack of solubility can cause problems such as grittiness, cloudiness and instability.

There are several ways to get around this. One is to improve solubility by heating or using an alternative solvent. Another is to use surfactants, emulsifiers and encapsulation to create nano-sized dispersions that aren't real solutions but resemble them.

Soap opera

The earliest attempts to overcome solubility problems could be said to have started with the development of soap, which helps to wash oils or grease from clothes or the skin. The poor solubility of oil and grease in water meant that water alone was not very effective for washing.

Early civilisations such as the Babylonians, Egyptians and Romans developed soap to circumvent this problem, although strictly speaking soaps do not work by improving solubility. Instead, soaps suspend or emulsify the dirt and, as soapy water will testify, the end result is not a clear solution.

Another early foray into manipulating solubility was the use of hot water to brew tea by improving the solubility of tea compounds in water. And the use of alcohol to improve solubility can be traced back as far as the Greeks, who mixed wine with herbs.

This was developed further in the 16th century by the Swiss physician Paracelsus who used distilled alcohol to prepare tinctures, or solutions of herbal extracts. Alcohol was also used to solubilise essential oils for use as fragrances.

Emulsions, the dispersions of oil droplets in water, have continued to be a mainstay of using materials with poor solubility. For example, sunscreens are generally only soluble in oils and early sunscreen products were often oil-based and were greasy and unpleasant to use. More recently, sunscreens have been dissolved in special, solubilising oils which can then be emulsified in water forming a cream or lotion that is much more pleasant to use. However, true solutions that are clear are generally not possible.

While both these approaches to improved solvency and emulsions can be used in foods and beverages, they are not always ideal. For example, it is not always desirable to include alcohol in a beverage and emulsions are no use where a product needs to be clear.

Beverages already successfully utilise a variety of soluble materials - from solids such as citric acid, to gases such as carbon dioxide in a carbonated beverage. However, if insoluble solids or liquids are to be added, then problems with clarity or stability can ensue. Examples include essential oils (a common component of flavours), oil-soluble vitamins such as vitamin A or vitamin E, or largely insoluble materials such as co-enzyme Q10.

However, recent advances mean that solubility problems can now be overcome without compromising product appearance or stability.

Modern approaches to tackling solubility problems include the synthesis of variants with different solubility properties: encapsulation, either on a molecular basis, or in micelles, microemulsions or other nano-structures; and the use of very finely dispersed, nano-sized solids.

Watson Foods, based in West Haven, Connecticut, has recently developed a form of vitamin E called Clear-E that forms a micellar dispersion in water. It uses a very finely dispersed form of vitamin E supported on a matrix and although the vitamin E is not truly solubilised, it gives every impression of being so. Clear, stable beverages can be produced using Clear-E that do not give problems with stability or ring formation.

Adumim Food Ingredients of Tel Aviv, Israel, has developed a flexible approach to solubilising oils, and oil-soluble materials, in water. Its Nutralease technology allows many materials that are currently difficult to use in clear beverages to be used in beverages without causing stability problems or affecting clarity. These include betacarotene, essential oils, vitamin A, vitamin D, vitamin E, lycopene, and phytosterols.

Liquid encapsulation

Nutralease uses a patent-pending nano-sized liquid encapsulation system that is also finding application in the pharmaceutical world to improve bioavailability. The improvements that can be attained in solubility also mean that the technology is very easy to use in a manufacturing environment, and does not require specialised mixers or other equipment.

Nutralease betacarotene is easily stirred in without the need for high shear mixing, and a perfectly clear solution of betacarotene results. The orange colour comes from the betacarotene itself and is not influenced by the use of Nutralease technology. By comparison, a conventional cold water soluble betacarotene leads to the formation of a very cloudy liquid.

A recent innovation using Nutralease was the launch of Canola Active, a canola cooking oil that contains phytosterols, solubilised using Nutralease. Phytosterols, known for their ability to help maintain healthy cholesterol levels, are virtually insoluble in oil and this product, which is completely transparent, would not be possible without the use of advanced solubilising technology.

Another approach to altering a material's solubility is molecular encapsulation. Valens, based in Ljubljana, Slovenia, has developed and patented Q10 Vital, which uses cyclodextrin as a molecular carrier for co-enzyme Q10, a material that is insoluble in water.

Cyclodextrin, however, is soluble in water and encapsulates the molecules of co-enzyme Q10 allowing a solution in water to be formed. This means that it can be used in beverages and other foods simply by stirring into the formulation.

The future of solubilisation has only just begun. With the appearance of the new technologies described here we can expect the arrival of numerous new products, especially in the beverage and dairy areas.

The recent surge in interest in healthy, functional foods and beverages means initial interest might focus on new product formats using nutriceuticals, but future trends are likely to include the launch of products with improved bioavailability, due to improved absorption of more soluble forms of nutrients.

We can also expect to see cross-over to and from developments in the pharmaceutical world, where bioavailability is a key concern.

''For further information, please contact

Neil Forbes, technical sales representative at Cornelius Health & Nutrition.

Tel: +44 7803 798150

Email: neil.forbes@cornelius.co.uk''

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