Which of the following is a common indicator of food spoilage?

A color change in food is a common indicator of spoilage because it often suggests that chemical changes are occurring, which can result from microbial growth or enzymatic activity. Different types of spoilage microorganisms can lead to discoloration, which signals that the food may no longer be safe to consume. For example, fruits may turn brown due to enzymatic browning or oxidation, while meats can develop a dull, grayish hue as bacteria grow and produce pigments.

In contrast, a fresh smell typically indicates that food is still good to eat. A firm texture is generally associated with freshness in products like fruits and vegetables, where softness can point to spoilage. Low pH can signify fermentation or spoilage, but it is not a universal indicator across all food types and can also be present in safely processed foods such as pickles. Therefore, a color change serves as a more general and widely recognized sign that food has deteriorated.