"Our results can guide industry in selecting sucrose substitutes for chocolate, in developing alternative formulations, and optimisation of their processing methods," lead researcher Professor Gurbuz Gunes told FoodNavigator.com.
Sales of so-called "diet candy" reached $495m in 2004. And while that dwarfs in comparison to sales of regular chocolate and non-chocolate candies, the diet candy market's growth has far outpaced that of its full-calorie counterparts.
According to a recent report from market research firm Packaged Facts, between 2000 and 2004, diet candy had a 34 per cent compound annual growth rate (CAGR). By comparison, chocolate had a CAGR of 3.9 per cent, while non-chocolate candy actually suffered from a negative 2.5 per cent CAGR.
The new research, published in the journal LWT - Food Science and Technology (Vol. 39, pp. 1053-1058), investigated the effects of substituting the polyols, maltitol, isomalt, and xylitol, for sucrose in molten chocolate.
Polyols provide the same bulk as sugar but are sugar free, do not promote tooth decay, and are used in a wide range of foods including chewing gum, candies, ice cream, baked goods, and fruit spreads.
This is not the first time that people have looked at replacing sugar with polyols in chocolate. Indeed, chocolate bars for diabetics are already available sweetened with sorbitol, while others have released products sweetened with erythritol.
But this is the first time, said Gunes, that the focus has been on the rheological properties of chocolate with these specific sweeteners and compared them to each other.
Rheology refers to the deformation and flow characteristics of the molten chocolate in terms of viscosity and friction.
"Molten chocolate is a dense suspension consisting of non-fat particles (sucrose, cocoa, milk) dispersed in cocoa butter as a continuous phase," explained lead author Ahmet Sokmen from the Istanbul Technical University. "Determination of rheological properties of chocolate is important in manufacturing process for obtaining high-quality products with well-defined texture."
The researchers prepared molten chocolate samples by melting cocoa butter and then adding cocoa powder and the respective sweetener. Finally, lecithin and more cocoa butter were added. The following companies provided the ingredients: Pelit Chocolate & Pie GmbH (cocoa powder, cocoa butter, and lecithin); Elit Chocolate and Confectionary GmbH (sucrose); Dora Foreign Trade GmbH (maltitol and isomalt); and Perfetti Van Melle Food Industry GmbH (xylitol).
Samples of chocolate were prepared using a range of particle sizes, and the resulting chocolate evaluated by measuring particle size distribution, viscosity, yield stress and flow behaviour.
Sokmen and Gunes report that the viscosity was dependent on both the type of polyol used and the initial particle size.
"Maltitol resulted in similar rheological properties of chocolate to sucrose, and thus it may be recommended as a good alternative to sucrose in chocolate formulations," they report.
"Chocolate with isomalt resulted in higher plastic viscosity while xylitol resulted in higher flow behaviour index."
Generally, larger particles were found to produce better rheological results from a manufacturing point of view, but these could possibly have adverse effects on the sensory properties of the chocolate, said the researchers.
Chocolates made using xylitol and may be rejected by consumers, they said, because of xylitol's intense cooling effect in mouth.
Indeed, rheological and sensory properties represent the two major challenges for such sugar-free chocolates, said Gunes, which are ultimately related to manufacturing cost and consumer acceptance.
"Considering our results and information in literature the most promising sweetener seems to be maltitol," he told FoodNavigator.com.
French-based company, Roquette, producers of the Maltisorb crystalline maltitol, obtained by hydrogenation of maltose, is said to be the leading polyol in many countries for this specific market. Maltisorb is reported to be already used in some chocolate products.