When an apple is cut (or bruised), oxygen is introduced into the injured plant tissue. When oxygen is present in cells, polyphenol oxidase (PPO) enzymes in the chloroplasts rapidly oxidize phenolic compounds naturally present in the apple tissues to o-quinones, colorless precursors to brown-colored secondary products. O-quinones then produce the well documented brown color by reacting to form compounds with amino acids or proteins, or they self-assemble to make polymers. 

    yigepingguobeiqiekaihuobeipengshangshi

，jinrupingguoshoushangzuzhideyangjiuhuiyuqizhongdeyixiehuahewufashengfanying
，shizhibianchenghese。dangyangcunzaiyupingguozuzhidexibaozhongshi，yelvti（含有葉綠素和進行光合作用的地方）中(zhong)的(de)多(duo)酚(fen)氧(yang)化(hua)酶(mei)

，會(hui)迅(xun)速(su)地(di)將(jiang)天(tian)然(ran)存(cun)在(zai)於(yu)蘋(ping)果(guo)組(zu)織(zhi)中(zhong)的(de)酚(fen)類(lei)化(hua)合(he)物(wu)氧(yang)化(hua)為(wei)鄰(lin)醌(kun)。然(ran)後(hou)，這(zhe)些(xie)無(wu)色(se)化(hua)合(he)物(wu)就(jiu)會(hui)自(zi)我(wo)組(zu)合(he)為(wei)聚(ju)合(he)物(wu)
，或(huo)與(yu)氨(an)基(ji)酸(suan)或(huo)蛋(dan)白(bai)質(zhi)發(fa)生(sheng)反(fan)應(ying)，在(zai)蘋(ping)果(guo)組(zu)織(zhi)內(nei)生(sheng)成(cheng)一(yi)些(xie)深(shen)色(se)的(de)次(ci)級(ji)產(chan)物(wu)。

    In the home kitchen enzymatic browning can be prevented by either reducing PPO oxidation activity or lowering the amount of substrate to which the enzyme can bind. Coating freshly cut apples in sugar or syrup can reduce oxygen diffusion and thus slow the browning reaction. Lemon or pineapple juices, both of which naturally contain antioxidants, can be used to coat apple slices and slow enzymatic browning. In addition, both fruit juices are acidic and the lower pH that they bring about causes PPO to become less active. Heating can also be used to inactivate PPO enzymes; apples can be blanched in boiling water for four to five minutes to nearly eliminate PPO activity. (Be warned that cooking will affect the texture of the product.) 

    我wo們men可ke通tong過guo減jian輕qing多duo酚fen氧yang化hua酶mei的de氧yang化hua作zuo用yong或huo減jian少shao能neng夠gou附fu著zhe這zhe種zhong酶mei的de基ji質zhi數shu量liang
，來lai抑yi製zhi這zhe種zhong酶mei的de褐he色se化hua反fan應ying。給gei新xin鮮xian蘋ping果guo切qie片pian塗tu上shang糖tang或huo糖tang漿jiang，可ke減jian緩huan氧yang擴kuo散san，並bing借jie此ci放fang慢man褐he色se化hua反fan應ying速su度du。檸ning檬meng汁zhi或huo菠bo蘿luo汁zhi都dou含han有you抗kang氧yang化hua劑ji，也ye能neng抑yi製zhi變bian色se反fan應ying。此ci外wai
，這zhe兩liang種zhong水shui果guo汁zhi都dou屬shu酸suan性xing，它ta們men所suo產chan生sheng的de低dipH值也能降低多酚氧化酶的活性。雖然加熱會改變蘋果的組織結構，但是它能減除多酚氧化酶的活性--如果將蘋果放在沸水中煮上四、五分鍾，差不多就能消除多酚氧化酶的活性。

    Enzymatic browning is not unique to apples. PPO—a mixture of monophenol oxidase and catechol oxidase enzymes—is present in nearly all plant tissues and can also be found in bacteria, animals and fungi. In fact, browning by PPO is not always an undesirable reaction; the familiar brown color of tea, coffee and cocoa is developed by PPO enzymatic browning during product processing. 

    酶的褐色化反應並非單單出現在蘋果身上。幾乎所有的植物組織都含有多酚氧化酶
，多酚氧化酶還存在於細菌
、動物和真菌類植物身上。事實上，多酚氧化酶的褐色化反應並非總是多餘的：茶、咖啡和可可常見的暗色調，就是在產品加工處理期間，通過多酚氧化酶的褐色化反應添加上去的。