Acid attack

Xylitol is a low calorie, sugar free sweetener that is widely recognised as being not only non-cariogenic but also cariostatic (caries preventative). This substance has been the focus of dental health research for over 30 years, and during this period xylitol's functionality and dental benefits have been corroborated on every occasion.

It is evident that xylitol does not lower oral pH after consumption, as it is not fermented by the acidogenic (acid producing) bacteria in the oral cavity. Under normal circumstances, fermentation of dietary carbohydrates by the bacteria in the oral cavity contributes to a lowering of pH, which is strongly associated with caries (tooth decay).

Saliva is one of the body's natural defence mechanisms against tooth decay. It produces a buffering effect in the mouth which can help prevent oral and plaque pH dropping below the so called "critical pH" at which acid-mediated demineralisation of tooth enamel, and hence tooth decay, can occur. The beneficial oral environment thus created is enhanced by xylitol, which inhibits the bacteria most commonly linked with the carious process.

Key to xylitol's edge over other sugar free sweeteners is that it alone dramatically reduces the incidence of dental caries, and even reverses the disease itself by stimulating remineralisation. Recent scientific evidence suggests that it inhibits certain metabolic pathways found in Streptococcus mutans, and in particular the metabolic pathways responsible for sugar utilisation (including the transport mechanisms for various sugars implicated in the caries process). These bacteria are believed to be responsible for initiating tooth decay, so any progress towards inhibiting their actions would be very desirable.

Xylitol has also been demonstrated to prevent the expression of two of the most important enzymes that aid Mutans Streptococci in the synthesis of specific molecules called glucans and fructans. These molecules are exo-polysaccharides that have strong adhesive properties, and are associated with the initial attachment, and subsequent accumulation, of bacteria on the tooth surface. These adhesive macromolecules also play an important role in the development of the dental plaque matrix. Furthermore, regular exposure to xylitol has been shown to increase the proportion of soluble exo-polysaccharides excreted by the Mutans Streptococci, making the plaque itself more readily disrupted, and, therefore, easier to remove by brushing or through the constant washing action of saliva. As such, regular xylitol consumption is frequently associated with inhibition of the main cariogenic bacteria and dental plaque as a whole. Significant reductions in bacteria and total plaque quantities were observed after only two weeks of consumption.

New studies are being published that look at genetic variations and gene expression. Such studies may be in vitro or in vivo in design, and their main goal is to determine the way in which the cariogenic virulence factors observed in Streptococcus mutans are induced and expressed. The results of these studies are explained on the basis of gene expression in the presence or absence of various carbohydrates present in the diet.

chewing GUM

It is clear that one of the most appropriate vehicles for xylitol is chewing gum because concentrations within the oral cavity are maintained for a prolonged period.

The incorporation of xylitol into chewing gum has, therefore, become widely accepted. But it is by no means limited to this application area.

Xylitol has also been widely used in the manufacture of other food and non-food products, from confectionery, baked goods and dairy applications to toothpaste and cosmetics. Its benefits in these applications are multiple - for example, in cake recipes, xylitol in combination with other bulking agents yielded excellent results in terms of both the sensory and textural characteristics of the finished products. In particular, sponge cakes containing xylitol and polydextrose showed measurable improvements in size, structure and sensory properties. These sponges were preferred because they exhibited characteristics very similar to those containing traditional ingredients such as sucrose.

The use of all polyols, including xylitol, is regulated around the world. Although xylitol is permitted in almost all countries, its use varies significantly. In Europe, the directives regulating the use of xylitol as a sweetener and a food additive are: EC Directives 94/35/EC (concerning the use of sweeteners in food) and 95/2/EC (concerning the use of additives, other than sweeteners, in food). These directives stipulate that xylitol, together with the other polyols, may be used to replace sugar, or as a miscellaneous additive (such as a bulking agent or flavour enhancer), when it is not being used for its sweetening properties. If xylitol is used as a sweetener, the finished product must be either energy-reduced (at least 30% calorie reduction compared to a standard product) or produced with no added sugar.

On the other hand, if xylitol is used as a bulking agent, the finished product would not necessarily be limited to any specific category or claim, provided that xylitol is performing a technological function in the product.

CONTROLS

The forthcoming European Regulation on Nutrition and Health Claims will also affect the use of xylitol and other polyols. Its objective is to establish tighter controls on the use of health and nutrition claims. All nutrition and health claims will be evaluated by the European Food Safety Authority (EFSA), and any claims must be supported by adequate scientific evidence and should be understood by the average consumer.

Xylitol is expected to open up the possibility of the same nutritional claims being made for it as are made for other polyols. However, its dental health benefits will be substantiated before specific dental health claims will be permitted.

Nevertheless, the clear weight of evidence supporting the compound's anti-cariogenic action, coupled with the support of many of the world's dental associations, should mean we can make more meaningful product claims.

Christos Zacharis is xylitol and xylose scientific and technical affairs manager at Danisco Sweeteners: +44 (0)1737 773732