Pasteurization is a heat treatment process that involves heating milk to a specific temperature for a set period and then rapidly cooling it. Its role is to kill most of the 'foe' microorganisms (pathogenic bacteria like Salmonella, E. coli, Listeria) that can cause diseases, without significantly altering the milk's nutritional value or flavor. This process effectively reduces the microbial load, making the milk safe for consumption and extending its shelf life by slowing down spoilage caused by other microbes.