英语听力文摘 English Digest 558、为怎样防止面包变质？

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　　Generally speaking, refrigeration helps to keep food fresh. Fruits, vegetables, and dairy products all last longer if kept cool.

 

　　But don’t try to store a loaf of bread in the refrigerator if you want it to stay fresh–refrigeration is the quickest way to make bread go stale.

 

　　Stale bread，on this moment of science.

 

　　As bread ages, it develops the dry, crumbly texture¹ and leathery crust that define staleness. But staling isn’t simply a matter of the bread drying out. Bread can grow stale even if it’s sealed tightly enough that no water can escape from the loaf.

 

　　Bread stales when the starch² inside the loaf loses its ability to hold water. Chemical changes in the starch inside the loaf cause it to lose water. The water moves to the starch in the crust, which begins much drier than the rest of the loaf.

 

　　Of course, if the bread is left uncovered, the water escapes to the air.

 

　　Staling depends largely on the temperature the bread is stored at, since temperature affects the ability of the starch in the bread to hold water. The drop in water-holding capacity is slowest at temperatures below freezing, so frozen bread stales very slowly.

 

　　The starch’s water-holding capacity decreases more quickly at room temperatures, and most quickly at refrigerator temperatures, which are just above freezing. In one experiment, refrigerated bread staled as much in one day as bread stored at room temperature staled in six.

 

 

　　怎样防止面包变质？

 

　　一般说来，冷藏有助于保持食品新鲜。如果冷藏，水果、蔬菜和乳制品均可以保鲜更久一点。

 

　　但是如果你想让面包保持新鲜，千万不要把它放进冰箱——冷藏是让面包变质最快的方法。

 

　　今天科学一刻主题：变质的面包。

 

　　面包放的久了，会变干变脆，表皮变韧，这说明面包变质了。但是变质不仅仅是面包变干那么简单。即使面包密封，没有水分流失，也会变质。

 

　　面包内部的淀粉失去锁水功能，面包就会变质。淀粉内部的化学变化导致面包水分流失。水分向面包皮上的淀粉转移，面包皮开始变得比别的地方更加干燥。

 

　　当然，如果面包没有包装，那么水分就散失到空气中去了。

 

　　变质速度很大程度上取决于面包贮存的温度，因为温度影响面包淀粉的锁水能力。冰点以下时，锁水能力下降速度最慢，所以冷冻面包变质速度非常慢。

 

　　室温下，淀粉的锁水能力下降得快一些，而在冷藏温度下，即略高于冰点温度，下降得最快。一项实验表明，面包冷藏1天就会变质，室温下6天才会变质。

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