Plant pigments as pH indicators in cooking

Abstract

Controlling acidity comes up often during cooking. Food’s acidity can be discussed in connection to using vinegar, marinade or baking soda in cooking. One seldom considers that acidity affects the food’s colour and thus its appeal. Colour is especially significant for ready-made foods. Berry jam or juice that is too pale or too dark does not look fresh or appealing. Many of the foods that lose their colour easily contain nature’s own pH indicators, anthocyanins. The workshop detailed in this article explores discolouration of anthocyanins with the help of different methods. Anthocyanins offer many points of discussion for chemistry classes, because in addition to their indicator properties, anthocyanins are also flavonoids and food additives. The work instructions are mainly aimed at grades 7 to 9. The chemistry part involving anthocyanins is suitable for upper secondary school as well, since it is challenging. The article details a demonstration that motivates towards inquiry-based work and two alternative work instructions.