Everyone has seen a piece of fruit turn brown after being cut. Have you ever wondered why that happens? It is a common phenomenon that occurs due to a chemical reaction called enzymatic browning. The appearance, flavor and nutritional value of the fruit are all affected by this reaction.
Some fruits, such as apples, pears, bananas, avocados and peaches, are more prone to enzymatic browning than others. These fruits contain high levels of an enzyme called polyphenol oxidase, or PPO for short. __1__
This causes a chain of chemical reactions that ultimately transforms the phenolic compounds into melanin, turning the fruit brown. Moreover, when fruit is bruised due to temperature changes or other external factors, the damaged cells break open and come into contact with air. __2__
Photo: Adobestock 照片：Adobestock
大家都曾看過水果切片後變成褐色。你有沒有好奇過那為什麼會發生呢？這是個因為酶促褐變這種化學反應而發生的常見現象。水果的外表、味道以及營養價值都會受到這種反應的影響。
有些水果—像是蘋果、梨子、香蕉、酪梨和桃子—比其他水果更容易發生酶促褐變。這些水果有高含量的多酚氧化酶（簡稱PPO）這種酶類。當這些水果被切開，內含的PPO會與空氣中的氧氣相互作用。
這導致一連串的化學反應，最終將酚化物轉變為黑色素，而黑色素將水果變成了褐色。此外，當水果因為溫度變化或其他外部因素而碰傷時，受損的細胞會碎開並接觸到空氣。因此，碰傷的部分轉變成褐色，因而影響到整個水果。
Photo: Adobestock 照片：Adobestock
Practical Phrases
1. be prone to + N/V 易於……
prone a. 易於……的，有……傾向的
People are prone to eat junk food when they are in a bad mood.
人們心情不好時，往往會吃垃圾食物。
2. break open 碎裂，破裂
The coconuts fell from the tree and broke open.
那些椰子從樹上掉下來，裂開了。
Words in Use
1. phenomenon n. 現象（單數形）
phenomena n. 現象（複數形）
A rainbow is an optical phenomenon.
彩虹是一種光學現象。
2. reaction n. 反應
a chemical reaction 化學反應
Burning wood into ash is a kind of chemical reaction.
將木頭燒成灰是一種化學反應。
3. flavor n. 味道，風味
I like to add pepper to enhance the flavor of my soup.
我喜歡加胡椒來提升湯品的風味。
To be continued tomorrow（明日待續）
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本文出自常春藤解析英語雜誌: www.ivy.com.tw
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