Question

Given below is the step-by-step process in the formation of yoghurt (curd) in a bioreactor.

(a) Why does the pH start decreasing a while after the mixture is incubated at 37-44°C?

(b) From the flowchart, identify two systems that the bioreactor would have. Give a reason .

Answer 1

(a) As the bacteria starts to grow, it uses up the oxygen in the system. 

After a while, the oxygen gets used up and anaerobic respiration begins which leads to the formation of lactic acid, causing a decrease in the pH.

(b) Oxygen delivery system: After the starter culture is added, oxygen is also added which will need a delivery system. 

Stirrer: Once oxygen is added, the system would need to be mixed thoroughly so that oxygen is available throughout the bioreactor. 

Sterilization unit: Milk needs to be sterilised before addition of the starter culture to remove any other microorganisms already present in it.