Effects of cultivation conditions on biofortification of yogurt with natural folate by Propionibacterium freudenreichii

In this study, Propionibacterium (P.) freudenreichii was used for the folate production by co-culturing with traditional yogurt starter cultures in synbiotic yogurt and then it was compared to control yogurt containing only LAB starters. First, effects of process variables, including two probiotic strains, inoculum size, inulin concentration, milk fat percentage, sunflower oil content, fermentation temperature and storage time of incubation at 4 °C on folate production by P. freudenreichii were investigated using screening method of Plackett-Burman design. Then, optimization of folate production process was carried out using three main effects of inulin concentration, fermentation temperature and storage time at 4 °C using central composite design. Analysis of variance showed that the models were highly significant ( p  ≤ 0.05) and folate production affected by the three factors. Optimized folate production by P. freudenreichii ssp. shermanii in yogurts was achieved after 12 d of storage at 4 °C in 2% (w/v) skim-milk inulin as prebiotic and fermentation temperature of 38.6 °C. Reconfirmation assays showed that the highest produced folate included 39.2 ± 0.7 μg 100 mL-1 in FW yogurt containing P. freudenreichii ssp. shermanii under the highlighted optimum conditions, which increased by 49% of the total folate production, compared to control yogurt, which contained only LAB starters. Furthermore, textural properties were assessed using texture analysis. Coculture of P. freudenreichii with traditional yogurt starter culture and addition of inulin to yogurt samples increased hardness, consistency and cohesiveness values in yogurt samples. Results showed that by co-culturing of P. freudenreichii ssp. shermanii in yogurt, in addition to producing a probiotic product, also increases the amount of folate production compared to control yogurt, which contained only LAB starters.