How does blanching stop enzymes from causing discoloration and off-flavours in vegetables?

Blanching prevents discoloration and off-flavours in vegetables by utilizing high temperatures to inactivate natural enzymes that would otherwise catalyze spoilage reactions after harvest.12

Because enzymes are protein molecules, they are highly sensitive to heat. When vegetables are exposed to temperatures between 88 °C (190 °F) and 100 °C (212 °F) for a short duration, the heat causes denaturation—a process where the enzyme's structure is destroyed, rendering it unable to function.23

By effectively neutralizing enzymes such as polyphenoloxidase, which is responsible for browning and off-flavours, or lipoxygenase, which can destroy nutrients and create undesirable aromas, blanching preserves the quality of the produce before it undergoes further food preservation methods like freezing, drying, or canning. The success of this process is often verified by measuring the residual activity of the enzyme peroxidase.124