Adding Lactobacillus bulgaricus to milk can help to ferment the milk and produce lactic acid, which can change the pH of the milk and lead to the formation of yoghurt. This bacterial strain is commonly used in the production of yoghurt and can help to promote its characteristic texture, flavor, and nutritional properties. The use of Lactobacillus bulgaricus can also help to improve the digestibility of dairy products and support gut health by increasing the amount of beneficial bacteria in the digestive tract.