Study of the microbiological characteristics of fermented dairy probiotic beverage containing propionic acid after fermentation and during cold storage

The objective of this research was to produce fermented dairy beverage with Propionibacterium freudenreichii ssp. shermanii and study the microbiological characteristics immediately after fermentation and during cold storage. In this study، impact of two process variables of incubation temperature and inoculation ratio on microbiological characteristics was studied by full factorial design. For the preparation of the fermented dairy beverage، a mixed culture of Lactobacillus acidophilus and Propionibacterium freudenreichii ssp. shermanii was grown at the ratio of 1:2، 1:4 and 1:8 and incubation was performed at 30، 35 and 40°C until the pH reached 4 ± 0. 1. Cell count of L. acidophilus was conducted on MRS Agar and incubation at 37 °C. Enumeration of P. freudenreichii ssp. shermanii was done on sodium lactate agar (NaLa agar) medium and incubation at 30 °C. In the most suitable condition for propionic acid production، profile of viability of microorganisms was determined in intervals of 0، 7، 14، 21 and 28 days. Also، phase separation of produced beverage was studied during the first week of storage at 4°C. The maximum viable cell count of P. freudenreichii ssp. shermanii was occurred by inoculation ratio of 1 to 4 and incubation temperature of 30 °C. There was an adverse and significant (P < 0. 05) relationship between viability of P. freudenreichii ssp. shermanii and incubation temperature. The maximum cell count of L. acidophilus was observed in a mixed culture of L. acidophilus and P. freudenreichii ssp. shermanii at ratio of 1 to 8 and incubation temperature of 35°C. Considerable decreased cell counts of P. freudenreichii ssp. shermanii and L. acidophilus were obtained during the first and the last weeks of cold storage، respectively.