1. Lowering pH:

* Direct effect on bacteria: Most bacteria thrive in a neutral pH range (around 7). Lowering the pH to a more acidic environment (like what citric acid does) creates an unfavorable condition for many bacteria.

* Disrupting cell function: The acidic environment can disrupt the delicate balance of pH inside bacterial cells, affecting their ability to function properly. This includes interfering with enzyme activity and essential metabolic processes.

2. Inhibiting growth:

* Decreasing nutrient availability: Some preservatives, including citric acid, can bind to essential nutrients needed for bacterial growth, making them less available for bacterial use.

* Interfering with metabolism: The acidic environment can directly interfere with bacterial metabolism, making it difficult for them to produce energy and grow.

3. Destroying bacteria:

* In some cases, the acidic environment can directly damage bacterial cells, leading to cell death. This is particularly true for certain types of bacteria that are more sensitive to pH changes.

In short, citric acid and other preservatives lower the pH of food, creating an environment that is hostile to many bacteria, inhibiting their growth and sometimes even destroying them.

Note: Different bacteria have different tolerances to acidity. Some bacteria can survive and even thrive in acidic conditions, making the choice of preservatives and their concentrations important for effectively inhibiting spoilage.