Which of the following is an indicator of food spoilage?

A bad smell is a key indicator of food spoilage because it often results from the growth of bacteria, mold, or yeast, which produce compounds that create unpleasant odors. When food spoils, the natural processes of decay and bacterial action lead to the breakdown of food materials and the formation of off-putting substances. This unpleasant smell alerts consumers that the food may be unsafe to eat, as it can indicate foodborne pathogens that could cause illness.

In contrast, pleasant smells, good texture, and bright colors typically signal that food is fresh and safe for consumption, as these attributes indicate a high quality in food products that are still within their shelf life.