Propionic Acid Bio-Fortification of Yogurts by Adjunct Culture of Propionibacterium freudenreichii

Background and Objective: Propionic acid bacteria are useful microorganisms that can produce beneficial food compounds. These bacteria mainly produce propionic acid that decrease the microbial population and growth along with increasing the shelf life. Propionibacterium freudenreichii was applied to produce propionic acid in yogurt in this study. Material and Methods: First, the process variables like inoculum percentage, strain type, milk fat and inulin amount, fermentation temperature, sunflower oil quantity, and refrigerated duration on propionic acid production by Propionibacterium freudenreichii was evaluated using Plackett-Burman design as a screening method. Next the acid production was optimized by a central composite design with 3 major factors of seed size, concentration of inulin, and refrigerated storage. Results and Conclusion: Analysis of variance showed that the models have been significant (p≤0.05). They represented that propionic acid production was influenced by three main factors. Optimized propionic acid production in yogurts by Propionibacterium freudenreichii ssp. shermanii (108 CFU. ml-1) was observed in 21 days after of refrigeration of skim-milk 2% (w v -1), inulin (3% w v-1) and incubation temperature of 43 °C. Reconfirmation test showed that the highest produced propionic acid was 12.53 ± 0.24 mg l-1in yogurt, which increased production up to 6.2 time. Results showed that Propionibacterium freudenreichii ssp. shermanii increases propionic acid contents in synbiotic yogurts containing inulin.