What's the difference between food contamination and food spoilage?

Substance added intentionally or unintentionally that (1) makes food unfit for human consumption, such as animal droppings,biocides, disease causing microorganisms or insects, dust, pests, and other foreign bodies or impurities, (2) is added only to increase the bulk or weight of food, such as water in milk and starch in ketchup, or (3) is food but is in wrong place, such as a bean in can of peas can be all termed as contamination.

Whereas, Food Spoilage can be defined as a disagreeable change in a food's normal state. Such changes can be detected by smell, taste, touch, or sight of the food. These changes are due to a number of reasons -- air and oxygen, excessive moisture, light, microbial growth, and temperature.