Processing (including cooking) of food is an important aspect of food—not least because of the effect on secondary natural products. Four of the most widely used (and most significant) types of processing are heating, freezing, drying and fermentation. While a primary function of each is the preservation of food and the prevention of microbial spoilage, they each also have an effect (directly or indirectly) on the secondary natural products that are present. In addition, some compounds are formed de novo as a consequence of processing and these present a challenge. In addition to the effect of processing on secondary natural products, it can also impact upon food macro and micronutrients and change the nutritional profile of foods. Processing can remove or degrade some natural toxicants. In addition, a number of natural products are subjected to enzyme-mediated modification and processing can alter enzyme activity and specificity thereby changing the profile of compounds that are present.