Biochemical Characterization of Microbial Isolates and Effect of Concentration and Incubation Time of Plant and Cow Milk Yoghurt using Response Surface Methodology

The objective of the research was to evaluate the biochemical characteristics of the various microbial isolates used in the production of plant based yoghurt, the optimal growth temperatures and the effect of incubation time and inoculum concentration on the taste and desirability of the yoghurt. Pure cultures of five (5) microbial strains (Lactobacillus acidophilus; Lactobacillus bulgaricus; Lactobacillus casei; Lactobacillus lactis; Streptococcus thermophilus) were obtained from commercial yoghurt and evaluated for their biochemical characteristics, bacterial growth temperatures and synersis. The isolated organisms were used to ferment plant-based milk product produced from blends of tigernut, Dates and Coconut. Response Surface Methodology (Face centered composite design) was used to obtain an optimized ratio formulation of 0.167 for coconut, 0.667 fortigernut and 0.167 for dates. Bacterial growth temperatures were evaluated at 4°C, 27°C, 37°C,40°C, 45°C and 60°C respectively. Results showed that full bacterial growth was noticed at temperatures of 40-45°C. The taste of the yoghurt improved from 6.58 to 6.71 when the incubation temperature changed from about 45°C to 44°C and the duration of incubation changed from 15.4 hrs to 14.7 hrs.