英语四级听力mp3下载：为何腰果不带壳销售

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Why Cashews Aren’t Sold In The Shell

Part of the fun of eating almonds or pecans is cracking the shell and getting the nut. But, some nuts, like cashews, are almost always sold shelled and roasted. Why aren’t cashews sold in the shell?

Cashews are in the same family as poison ivy and poison sumac. Like the others in this family, the cashew plant contains powerful chemical irritants, so handling and eating raw cashews will cause the familiar itchy skin reaction in people sensitive to the chemicals. People who are sensitive to one plant in the family, for example poison ivy, are likely to be sensitive to others.

Why don’t we get a reaction when we eat cashew nuts, then? The irritants are found in the shell oil, but not in the nuts themselves. Handling the shell or eating a nut with shell oil on it can cause the reaction.

This is why they’re sold shelled, but why are they roasted? Roasting at high temperature destroys the shell oil, so commercially sold nuts will not trigger a reaction. But, cashew nuts that are still in the shell or that are shelled and roasted at home at lower temperatures may be contaminated with the oil, so, shelling raw cashews is about as much fun as handling poison ivy.
为何腰果不带壳销售

吃杏仁和胡桃的部分乐趣来源于敲碎外壳后得到果仁。然而，有些坚果，比如腰果，通常会去壳烤熟销售。为什么腰果会不带壳销售呢？

腰果和毒葛与毒漆树同属一科。与同科其它植物相似，腰果树含有强烈刺激性化学物质，所以处理和吃掉生腰果，会使那些对化学物质敏感的人皮肤产生瘙痒反应。对某一科某种植物过敏的人，比如对毒葛过敏，很有可能会对同科的其它植物也过敏。

那当我们吃腰果时为什么没有反应呢？那是因为刺激物质存在于外壳油脂中，而果仁中却不含有。所以处理外壳或者吃带有外壳油脂的腰果时，就会引起（瘙痒）反应。

这就是为什么腰果不带壳售卖的原因，但是又为什么要烤熟呢？因为高温烘烤可以破坏果壳油脂，所以商业销售的腰果仁不会造成反应。带壳的或者在家中去壳并低温烘烤后的腰果可能仍会受到果壳油脂的污染，所以给生腰果去壳和处理毒葛一样有趣。

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