Browning of foods Available to Purchase

With a modest selection of reagents, equipment and test foods — some of which will be normally stocked in the kitchen — students can carry out these practical tests. Most of them will be aware that certain foods develop a brown pigmentation during processing, preparation and cooking. A number of different reactions can cause this browning; reactions between amino‐acids and sugars are responsible for the surface colour of baked bread, caramelisation of sugars produces the colour of toffee and oxidation of some food components can produce discolouration in orange juice. Another familiar browning reaction is that which produces rapid discolouration in cut or bruised fruits and vegetables such as potato, mushroom and apples. These reactions — known as ‘enzymic browning’ because they are catalised by an enzyme present in the food — are the subject of this article.