The functionality of African streptococcus thermophilus and streptococcus infantarius subsp. infantarius in milk fermentation

Abstract

Fermentation serves a key role in inhibiting spoilage microorganism through acidification and production of antimicrobial compounds. The technological information on properties of Streptococcus infantarius sub sp. infantarius which is predominant in most African fermented is very little. This study was therefore carried out to determine the functionality of selected African Streptococci strains in fermented dairy products. Pasteurized milk samples from camels and cows were inoculated with different strains and a selected combination at a rate of 3 % v/v and incubated at different temperatures of 25°C, 30°C, 37°C, and 45°C for 9 hours. Analysis was done after every 3 hours for pH and titratable acidity while viscosity was done after incubation and cooling of the product. The different fermented milk samples were subsequently evaluated for consumer acceptability. Milk inoculated with both African type Streptococcus thermophillus (146A8.2)and Streptococcus infantarius sub sp. infantarius CJ 18 (9377), and incubated for nine hours recorded the highest amount of titratable acidity of 0.97 for the camel milk and had the least pH value of 4.12 for cow milk compared to the other strains. The cow milk had the highest viscosity level of 59.64 cPs compared to camel milk which was 29.44 cPs. The levels of titratable acidity and viscosity depended on the strain and incubation temperature. The African type Streptococcus thermophillus (146A8.2) and Streptococcus infantarius sub sp. infantarius CJ 18 (9377), isolated from fermented camel milk had good technological properties that are useful as starter culture for development of fermented milk products.