Formulation optimization of a potentially prebiotic low-in-oil oat-based salad dressing to improve Lactobacillus paracasei subsp. paracasei survival and physicochemical characteristics

•Development of a physically stable low-in-fat oat-based probiotic dressing.•RSM established the relationships between emulsion ingredients and characteristics.•In aged emulsions oat flour and xanthan ensured probiotic viability equal to inulin.•Oat flour and xanthan improved physicochemical characteristics of the emulsions.•Dressings can be exploited as potential fibre and probiotic carriers.

The concept of this study was to develop a low-in-oil salad dressing emulsion, based on oat flour, that combines the flour health-promoting potential of fibre and growth support of the probiotic Lactobacillus paracasei subsp. paracasei DC412 with the functional properties of oat flour e.g. emulsion stabilization and thickening ability. Probiotic viability, following emulsion storage and enzymatic treatment, was sustained in presence of oat flour at levels close to those found for inulin. The dressing emulsion was further investigated by applying response surface methodology to establish the relationships between the main factors (storage time, and oil, xanthan and oat flour content), on one hand, and the response variables (probiotic cell count before and after treatment with gastrointestinal track enzyme fluids, consistency index (K), and mean droplet diameter (d43), on the other. The optimum formulation (g/100 g) found was: oil (20), xanthan (0.475) and oat flour (3.0); viable cell counts of emulsions after 7.5 weeks of refrigerated storage and treatment with simulated gastric and intestinal juices reached levels as high as 108 cfu/g. In addition to enhancing cell viability, oat flour incorporation led to an appreciable improvement of the emulsion rheological properties and physical stability.