Final answer:
The exact number of Lactobacillus bacteria in 1 litre of curd cannot be determined without microbial analysis. The presence of live, active cultures of Lactobacillus and Bifidobacterium is mentioned on commercial yogurt products, which aid in fermentation and have health benefits.
Step-by-step explanation:
The number of Lactobacillus bacteria present in 1 litre of curd can significantly vary depending on the production processes, the initial amount of bacteria added, and the conditions under which the curd was fermented, such as the specific temperature of incubation. It is challenging to provide an exact count without conducting a microbial analysis. However, it is known that commercially prepared yogurt often states the presence of "live, active cultures" including Lactobacillus and Bifidobacterium, which are both bacilli. These bacteria are central to the fermentation process, converting lactose into lactic acid and contributing to the health benefits of yogurt by promoting good digestive health and a well-balanced immune response. During the fermentation process, the Lactobacillus bacteria utilize lactose to produce lactic acid, lowering the pH and resulting in the curdling of milk into curd.
The approximation of bacterial content in commercial or homemade yogurt products would require a count of bacteria under a microscope in a controlled environment. As for health and safety standards, coliforms' presence would indicate contamination, and they are tested differently, e.g., using the most probable number method as shown in figure 9.14 in scientific studies, which is not directly applicable to dairy fermentation processes.