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段落1

NARRATOR

Listen to part of a talk in a food science class.

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段落2

FEMALE PROFESSOR

Everyone knows food can become spoiled—go bad and become inedible.

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Usually, the cause is harmful bacteria that grow naturally in food.

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段落3

So, one of the best ways to prevent food from spoiling is to slow down bacterial growth.

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But how do you do that?

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Well, what influences how fast bacteria grow?

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Mainly, it’s temperature and moisture.

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段落4

So if you want to prevent food spoilage, you need to slow bacterial growth by controlling these factors.

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Why’s controlling temperature so important?

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Because the bacteria that cause food spoilage grow fast at warm temperatures and more slowly at cooler temperatures.

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段落5

When your food is kept cool, it lasts longer, right?

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For example, fresh fish left out in the sun on a warm day will spoil in a few hours.

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段落6

But if you freeze the fish, it will keep for months and months, right?

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That’s because low temperatures drastically slow down bacterial growth.

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段落7

Now, I said that moisture’s another factor you need to control.

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And every living thing needs moisture, and bacteria are no exception.

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Food that’s high in water content provides the moisture that bacteria need to grow.

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段落8

Let’s, uh, let’s compare two different kinds of milk, okay?

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Let’s compare regular liquid milk with dried, powdered milk.

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Regular milk spoils quickly, right?

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But milk in powder form can be stored quite a long time…in fact, for years.

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Of course, bacteria are present in powdered milk too.

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段落9

But what’s different between powdered and regular milk is the water content.

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Powdered milk has had the water, the moisture removed, and without moisture bacteria can’t grow.

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And this isn’t true just for milk; just about any fresh food will spoil more quickly than a dried food.

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