The boom in functional and better-for-you soft drinks has resulted in the addition of many new active ingredients. Companies have to be sure that products retain claimed properties during their entire shelf-life. Melindee Hastie of product testing specialists RSSL looks at some of the challenges this presents.

New product development continues apace in the soft drinks sector, and it's no longer only fruit that is being added to juice products. Other natural products like green tea extracts, ginseng and omega-3 fatty acids are now being incorporated to produce fortified products.

Leaving aside the difficulties of substantiating health claims for these ingredients, there are plenty of other content claims that appear on labels, which means that nowadays a lot of hard science is needed to support the production of soft drinks.

One major problem for drink producers is that just because they can be sure of what goes into the product, they can have no guarantee of what is still there at the time of consumption. Many of the vitamins, antioxidants and other active ingredients are potentially unstable and prone to degradation both during processing and storage.

Stability testing is therefore a key element of any new product development process. Such studies involve storage of the product in appropriate conditions, with analysis at regular intervals to the end of the proposed shelf-life period.

Whilst a long history of vitamin addition means that much is already known about vitamin stability, far less is known about the stability in soft drinks of polyphenols, carotenoids, stanols, sterols and other such ingredients. So much depends on the composition of the drink, the form in which the ingredient is added, the acidity of the product, the type of packaging used, the conditions in which the product is packaged and stored and so on.

The vitamins most commonly added to soft drinks are in water soluble form. For example, Vitamin B1 (thiamine) is generally added to soft drinks as thiamine hydrochloride, which is more soluble in water than the other commercially available form, thiamine mononitrate. It is relatively stable in low pH solutions and therefore suitable for most fortified fruit drinks. Niacin (Vitamin B3) is also very stable, and research has indicated that this vitamin does not degrade in soft drinks during storage. Vitamin B12 is relatively stable to both atmospheric oxygen and heat when in acidic solution. However, the stability of Vitamin B12 is significantly influenced by the presence of other vitamins.

The greatest problems with instability arise with the other vitamins. Vitamin B2 (riboflavin) and folic acid are very sensitive to light, whereas Vitamin A (added as either retinol or as carotene) is sensitive to oxygen and acidic media. The stability of Vitamin C in fruit juices varies widely according to the composition and oxygen content of the product. Acidity and light also have an effect on ascorbic acid degradation such that the loss of Vitamin C during processing can be quite considerable.

There are of course, many other additives that have perceived health benefits and are increasingly being used as ingredients in foods, such as taurine, choline, glucosamine, carnitine, carotenoids and others. All of the general observations made about vitamins above apply to these too.

Stability is a complex issue and nothing can be taken for granted. It is possible, for instance, for an ingredient to be stable in a soft drink when packaged in a 1-litre bottle but less stable in a 500ml bottle, simply because the proportion of headspace air to liquid is greater in the smaller bottle, and therefore more able to react with the contents. It is only through testing that these factors can be revealed.

From a technical perspective, the challenge is not merely to retain the added ingredient in the product, but to do so in a way that does not compromise taste or product acceptability.

Several of the currently topical 'healthy' ingredients, such as fish oils, glucosamine, soya extracts and green tea, are hardly noted for being the best tasting. Even the most health conscious consumer is unlikely to sacrifice the immediate gratification of a pleasant taste for longer-term potential health benefits.

A number of ingenious approaches can be used to mask unpleasant flavours, and the best solution is highly dependent on the original product, both in terms of the concept and formulation. However, just because a solution may represent the best technical option, it may not be the best option from a commercial or conceptual perspective.

The issue of colours is worth considering. Screening programmes can be constructed to detect the use of natural colours, such as anthocyanins and carotenoids, synthetic colours such as Tartrazine, Ponceau 4R, and Sunset Yellow, and illegal colours such as Sudan Red, Orange G and Orange II. Given the recent discussions by bodies such as the UK's Food Standards Agency (FSA) regarding the use of certain artificial colours, it seems likely that more emphasis will be placed on colour screening in future.

Understanding the health claims that can be made, and what ingredient content statements must be made, is one of the big challenges for the soft drinks industry. Essentially, everything boils down to knowing exactly what has gone into the product, and how everything survives (or not) through its shelf life. With appropriate testing to verify that the added ingredients are as described, and neither lack what should be there or contain what should not, the manufacturer can at least substantiate the claims relating to content, even if the claims relating to benefits are harder to prove.

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