Enzymatic browning is a chemicalprocess occurring in fruits and vegetables that results in brownpigments. This can cause the fruits or vegetables to lose nutrients.However, this can be avoided by either addition of acids or bases orthrough application of heat.
The process can be done incontrolled environments in the laboratory. Below is an analysis ofhow carotenoids, chlorophyll, and anthocyanin react to laboratoryenzymatic browning.
Inthe first case, when carotenoids are heated in the laboratory, mixedwith alkalis or acids, they still maintain their brown color. On theother hand, broccoli when cooked in water in the laboratory turnsgreen, turns dull green when acids are added, and turns bright greenwhen an alkali is used.
Flavonoids such as red cabbage onthe other hand react differently in the lab when heat, alkali, oracids are applied. When heated in water they turn to a reddish/purplecolor. When acids (limejuice) are added, they turn bright red andwhen alkalis are used, they turn blue.
These three principles ofpreservation have little impact on nutrient levels. All three areways that people can use in order to preserve fruits and vegetables.However, blanching and refrigeration are the most common forms ofpreservation because the enzyme polyphenoloxidase enzyme responsiblefor the brown pigmentation is either inactivated by the heat orinhibited by low temperatures. When refrigeration or freezing isused, a return to normal temperatures leads causes the process toresume as the enzyme is only inhibited.