Effect of incubation temperature and inoculation ratio of starter culture on propionic acid production in dairy beverage fermented with propionibacterium

Increasing trends of overweight and obesity prevalence have prompted food producers to develop products that can enhance satiety signals. The role of short-chain fatty acids as satiety-inducing triggers seems to be of interest in this regard. The objective of this research was to investigate the impact of two process variables, namely, incubation temperature and inoculation ratio of starter bacteria, on propionic acid production in the fermented dairy beverages containing Propionibacterium immediately after fermentation and during cold storage. Fermented dairy beverage (FDB) samples were prepared using mixed cultures of Lactobacillus acidophilus and Propionibacterium freudenreichii ssp. shermanii at a ratio of 1:2, 1:4 and 1:8, repectively, at incubation temperatures of 30, 35 and 40°C, until the pH reached 4.0 ± 0.1. Propionic, lactic and acetic acid contents of the samples were measured immediately after fermentation using HPLC. The FBD samples were refrigerated for 28 days and the concentrations of the acids in the samples with the highest propionic acid content were measured. Sensory evaluation of the samples produced was made by 11 trained panelists using the hedonic scale. The maximum propionic acid content (w/w%) was observed in a mixed culture of L. acidophilus and P. freudenreichii ssp. shermanii at a ratio of 1:4 and an incubation temperature of 30 °C. It increased from 0.75 at day 0 to 1.2 at day 28 during storage at 4 °C. The incubation temperature had a statistically significant inverse effect (P<0.05) on the propionic acid production in the fermented dairy beverages.