Food Quality Chemistry

Beyond simply supplying nutrients, food also has a 'quality' that changes over time, and that quality is judged by several practical parameters: flavour, smell, texture, colour, and the extent of microbial spoilage. Every food contains enzymes naturally, and it is largely the action of these enzymes -- together with ordinary chemical reactions between the food and its environment (oxygen, moisture, light) and the action of microorganisms growing in or on the food -- that causes quality to change during storage. Not every such change is bad: some microbial changes are put to deliberate, beneficial use, such as milk being allowed to set into curd, or yeast/bacteria being used to raise flour dough into bread. But most of the changes that arise from microbial growth and environmental interaction during storage work against food quality rather than for it. The rest of this section works through five specific chemical mechanisms behind food-quality change and food additive chemistry in turn: the browning of cut fruit and vegetables, the rancidity of oils and fats, t …