Bacterial conjugated linoleic acid bio-fortification of synbiotic yogurts using Propionibacterium freudenreichii as adjunct culture

In this study, Propionibacterium freudenreichii was used for in situ production of conjugated linoleic acid (CLA) in yogurt. Firstly, effects of process variables, including strain type, percentage of milk fat, percentage of inoculum, quantity of sunflower oil, concentration of inulin, temperature of fermentation and time of storage at 4°C, on production of CLA by Propionibacterium freudenreichii were investigated using screening method of the Plackett–Burman design. Then optimisation of CLA production process was conducted using three major factors of milk fat percentage, inulin concentration and storage time at 4°C using central composite design. Analysis of variance established that the models were highly significant (P ? 0.05). The model demonstrated that the production of CLA was affected by these three factors. Optimised CLA production by Propionibacterium freudenreichii ssp. shermanii in yogurts was achieved after 17 days of storage at 4°C in skim-milk containing 1.75% (w/w) fat and 2.25% (w/v) inulin as prebiotic. Reconfirmation test established that at the highlighted optimum conditions, the highest concentration of produced CLA was 6.4 mg g–1 lipid in yogurt, which is a 256% increase in total CLA production, compared with control samples. Results demonstrated that Propionibacterium freudenreichii ssp. shermanii not only leads to production of synbiotic yogurts containing inulin but also increases CLA production in yogurts.