Why do peeled apples change color

The discoloration of peeled apples is caused by the oxidation reaction between polyphenols in the flesh and oxygen. The discoloration of apples is mainly related to factors such as polyphenol oxidase activity, oxygen concentration, temperature, pH, and cutting method. Apples contain abundant polyphenols and polyphenol oxidase. When apples are peeled or cut open, their cellular structure is disrupted, and polyphenol oxidase and polyphenolic substances undergo enzymatic browning reactions under the action of oxygen, producing brown pigments. This reaction occurs rapidly at room temperature, especially when the cutting surface is large. Polyphenol oxidase has the highest activity in a neutral environment, which is why soaking in acidic solution can delay discoloration. Low temperature environment can reduce enzyme activity, so refrigerated apples change color slower. There are differences in polyphenol content among different varieties of apples, and varieties such as Red Fuji are relatively more prone to discoloration. Metal cutting tools accelerate the oxidation process, while using ceramic cutting tools can reduce the degree of discoloration. Although discoloration does not affect food safety, it can lead to the loss of some nutrients. It is recommended to consume as soon as possible after peeling or take antioxidant measures. To delay the discoloration of apples, cut apples can be soaked in light salt water or lemon water, and enzyme activity can be inhibited by salt or acidic environment. You can also tightly wrap the cutting surface with cling film to isolate the air. It is recommended to refrigerate uncut apples for daily storage, and try to consume them within two hours after cutting. Apple discoloration is a normal phenomenon that does not affect its nutritional value, but may reduce appetite. Mastering the correct processing methods can better preserve the fresh taste and nutrition of apples.