Which of the following is a sign of food spoilage?

A sign of food spoilage is an off odor. This occurs when food begins to decompose due to microbial growth, enzymatic activity, or chemical reactions. Spoiled food often develops unpleasant smells as harmful bacteria or molds break down the organic matter, producing gases and compounds that create these odors. Recognizing off odors is crucial because it is a key indicator that food is no longer safe to eat.

In contrast, bright colors can sometimes indicate freshness, especially in fruits and vegetables. Firm texture is often associated with quality and freshness, as spoiled food typically becomes soft or mushy. A cool temperature is essential for preserving food, as inappropriate temperatures can either promote spoilage (if too warm) or help maintain the quality (if adequately cooled). Thus, while the other options can relate to the quality or preservation of food, an off odor is a definitive sign of spoilage.