Formulation optimization of a probiotic low-calorie chocolate milk and investigating its qualitative properties during storage

Due to concern regarding the consumption of high amount of sugar in diet and role of diet in combating overweigh and related disease, the aim of present study was to optimize a reduced calorie probiotic chocolate milk formula with suitable physicochemical properties. The formula comprising inulin, stevia (<i>Stevia rebaudiana</i> Bertoni), chia (<i>Salvia hispanica</i> L.) seed gum (CSG), and whey protein concentrate (WPC) which optimized using Box-Behnken design (BBD) and then enriched with an encapsulated probiotic strain <i>Lactobacillus acidophilus</i> (DSM1643). The independent variables included inulin (2-8%), CSG (0.1-0.5 %), stevia (50-100 % replacement of sugar), and WPC (1-3%). The dependent variables were selected as viscosity, average particle size, sedimentation percentage, and general acceptance. Optimization done toward achieving the highest viscosity and general acceptance and the lowest sedimentation percentage and average particle size. The optimal conditions were found to be 7.99 % inulin, 70 % stevia, 0.34 % CSG, and 1 % WPC. Under these conditions, the viscosity, sedimentation percentage, average particle size, and general acceptance of the product were equal to 40.69 mPa s, 2.2 %, 434.221 nm, and 5.1, respectively. Next, the chocolate milk was enriched with at 10⁹ CFU/g probiotic bacteria and evaluated. The probiotic strain was resistant to simulated gastrointestinal conditions and under this condition the free bacterial cells count declined by 8 logCFU/g while the encapsulated cells decreased approximate 3 logCFU/g. The bacteria count did not undergo a significant change until the 5th day of storage. The results showed that the inulin, stevia, CSG, and WPC at optimal concentrations and encapsulated probiotic bacteria could be simultaneously applied to produce a product with good properties. This formula could be considered as a new product with health improving properties, low calorie which is suitable for people suffering from diabetes and obesity.