Why are psychrotrophs relevant to pasteurized milk?

• A. They can grow at room temperature, causing rapid spoilage
• B. They can grow at refrigeration temperatures, causing spoilage and potentially producing enzymes that degrade milk quality
• C. They are killed by pasteurization
• D. They do not affect milk quality

Answer: (B)

Psychrotrophs are bacteria that can multiply at refrigeration temperatures, which is the storage condition for pasteurized milk. This makes them especially relevant because, after pasteurization, milk sits in cold environments where these organisms can grow and cause spoilage before the product is used or sold. In addition to growth, many psychrotrophs produce enzymes such as lipases and proteases that are heat-stable. Even though pasteurization may kill the cells, these enzymes can survive heat treatment and continue to degrade fats and proteins in the milk during storage, leading to rancid flavors, off odors, and texture changes. This combination of cold-tolerance and enzyme production is why psychrotrophs are a key concern for pasteurized milk quality.