Background and Objective: Prebiotics are food ingredients that induce the growth or activity of beneficial bacteria (Bifidobacteria and Lactobacilli). Galactooligosaccharide and tagatose are two main prebiotic compounds which are used in the food industry. Chocolate is widely consumed all over the world and could be used as an excellent vehicle for delivery of prebiotics. Furthermore, the incorporation of probiotics into chocolate, allows broadening the health claims of chocolate. The aim of the current study was to investigate the effect of tagatose and galactooligosaccharide on the physicochemical and sensory properties of milk chocolate and the survivability of Lactobacillus paracasei in the optimized formulation.

Material and Methods: Probiotic milk chocolate containing Lactobacillus paracasei were formulated by replacing a portion of the sucrose with the galactooligosaccharide powder and tagatose. For this purpose various concentrations of galactooligosaccharide and tagatose (2.5, 5 and 7.5% w w^-1) along with stevia were used in chocolate formulation. Nine formulations were examined to determine some physicochemical, mechanical and sensory properties in order to find the optimum concentrations of these components. The lyophilized Lactobacillus paracasei were incorporated in the optimal formulation of prebiotic milk chocolate. The viability of probiotic bacteria in milk chocolate was carried out during storage at 22°C for up to 6 months.

Results and Conclusion: In general, chocolate formulations with high levels of galactooligosaccharide, achieved the highest plastic viscosity and yield stress. The lowest viscosity and yield stress were observed for the samples containing high concentrations of tagatose and in control. In addition, galactooligosaccharide at higher ratios induced the least desirable sensorial effects, whereas tagatose improved the overall acceptability. It can be concluded that the overall acceptability of milk chocolate samples were with (7.5), tagatose: galactooligosaccharide ratios of 2.5%-2.5%, presenting the optimal applicable range as prebiotic compounds. Numbers of live Lactobacillus paracasei cells remained above 8.0 log CFU g^-1 until 6 months under ambient conditions. Milk chocolate was shown to be an excellent vehicle for the delivery of Lactobacillus paracasei, and the prebiotic ingredients galactooligosaccharide and tagatose did not interfere in its viability.

Conflict of interest: The authors declare no conflict of interest.