水果香甜味美,每个人都喜爱吃。水果在食用前,常常要先削皮,这样做既卫生又安全。可是水果削皮后,如不及时食用,则会产生果肉变色的现象。例如,在食用苹果、梨时常常会看到鲜嫩的果肉很快就变成棕褐色,极像铁生锈的样子,这是为什么呢?水果削皮后果肉与空气接触就会变成褐色,并且时间越长颜色越深,这一部分是由于水果中含有一种叫“鞣酸”(亦称单宁酸或单宁)的多酚类物质而导致的。这种物质一旦遇着铁制物品(如水果 Sweet and delicious fruit, everyone likes to eat. Before eating fruit, it is often necessary to peel it first, which is both hygienic and safe. However, peeling fruit, if not consumed in time, it will produce the phenomenon of discoloration of the flesh. For example, when eating apples and pears, you can often see that the tender flesh soon turns brown, much like the rusty iron. Why? When the fruit is peeled, the flesh turns brown with the air, And the longer the color, the darker the color, in part because the fruit contains a polyphenolic called “tannic acid” (also known as tannin or tannin). Once encountered in this material iron items (such as fruits