英语听力文摘 English Digest 316、罐装食品膨胀的原因

　　What Causes A Can Of Food To Swell¹?
罐装食品膨胀的原因
Most of us are cautious eaters.
If you’re munching² grapes, you’ll probably skip one that’s all shriveled and discolored in favor of the round, healthy ones. Likewise, when you choose a can of food at the supermarket, you’ll likely choose one that’s exactly can-shaped, not one that’s misshapen and swollen³.
There's a good reason for this.
A can of food can swell for two separate reasons. The first is what food scientists call “hydrogen swelling,” and it only happens to cans of acidic food such as tomatoes or citrus fruit.
The acids in the food begin to attack and dissolve the metal lining⁴ of the can, and one of the by-products of this chemical reaction is hydrogen gas. Because the can is sealed, the gas builds up, causing the can to swell.
The second reason a can swells⁵ is the result of poorly processed food. Before it’s canned, food needs to be sterilized⁶ to remove all the potentially dangerous microorganisms– especially those that can live inside a can without oxygen.
If some of these organisms are left behind, they can thrive in the can, spoiling the food and giving off carbon dioxide gas. In this case, carbon dioxide causes the can to swell.
Standing⁷ in the supermarket aisle⁸, there’s no way you can tell whether a can is swollen because of hydrogen or carbon dioxide gas, but that really shouldn’t matter.
Assume that the food has spoiled, inform the store manager, and choose a healthy, can-shaped can instead.

　　大多数人对吃的东西都很谨慎。
比如在吃葡萄时，你会选择圆圆的，健康的葡萄而不是那些枯萎变色的。同样地，当你在超市挑选罐装食品时，会选择包装完好的罐头，而不是那些畸形或膨胀的。
这样做是有原因的。
罐装食品膨胀有两种不同的原因。第一种就是食品科学家所说的“氢膨胀”，只有装有酸性食品的罐头才会发生这种现象，比如西红柿或柑橘类的水果。
食品中的酸性物质开始溶解罐的金属内层，这种化学反应会产生氢气。由于罐是密封的，气体逐渐积聚起来，使罐头膨胀。
第二种原因是糟糕加工的结果。在装罐之前，食品需要消毒，消除所有潜在的不安全微生物，特别是那些能够在无氧条件下生存的微生物。
如果这些生物留在罐头内，它们会大量繁殖，使食物变质产生二氧化碳气体。在这种情况下，就会是罐头膨胀。
站在超市的走道上，我们没有办法辨别罐头膨胀是由于氢气还是二氧化碳，但也没关系。假如食品已经变质，告诉商店的经理，然后选择一罐好的就可以了。

1 swell   

vi.膨胀，肿胀；增长，增强

参考例句：

• The waves had taken on a deep swell.海浪汹涌。
• His injured wrist began to swell.他那受伤的手腕开始肿了。

2 munching   

v.用力咀嚼（某物），大嚼( munch的现在分词 )

参考例句：

• He was munching an apple. 他在津津有味地嚼着苹果。 来自《简明英汉词典》
• Munching the apple as he was, he had an eye for all her movements. 他虽然啃着苹果，但却很留神地监视着她的每一个动作。 来自辞典例句

3 swollen   

adj.肿大的，水涨的；v.使变大，肿胀

参考例句：

• Her legs had got swollen from standing up all day.因为整天站着，她的双腿已经肿了。
• A mosquito had bitten her and her arm had swollen up.蚊子叮了她，她的手臂肿起来了。

4 lining   

n.衬里，衬料

参考例句：

• The lining of my coat is torn.我的外套衬里破了。
• Moss makes an attractive lining to wire baskets.用苔藓垫在铁丝篮里很漂亮。

5 swells   

增强( swell的第三人称单数 )； 肿胀； （使）凸出； 充满（激情）

参考例句：

• The waters were heaving up in great swells. 河水正在急剧上升。
• A barrel swells in the middle. 水桶中部隆起。

6 sterilized   

v.消毒( sterilize的过去式和过去分词 )；使无菌；使失去生育能力；使绝育

参考例句：

• My wife was sterilized after the birth of her fourth child. 我妻子生完第4个孩子后做了绝育手术。 来自辞典例句
• All surgical instruments must be sterilized before use. 所有的外科手术器械在使用之前，必须消毒。 来自辞典例句

7 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

8 aisle   

n.（教堂、教室、戏院等里的）过道，通道

参考例句：

• The aisle was crammed with people.过道上挤满了人。
• The girl ushered me along the aisle to my seat.引座小姐带领我沿着通道到我的座位上去。