Why does the browning reaction occur in sponge cakes?

The browning reaction in sponge cakes occurs primarily due to the Maillard reaction and caramelization during baking. The Maillard reaction involves the interaction between sugars and amino acids, leading to the development of complex flavors and a golden-brown color. As the cake heats, sugars also caramelize, further contributing to the browning and enhancing the cake's taste and aroma. This process is essential for achieving the desired texture and visual appeal of the finished product.