英语时差:果胶是什么？
It's pretty easy to guess what most of your food is made of. The meat in your hamburger probably came from a cow, the bun was made from grain, the ketchup from tomatoes, and so on. There is one kind of food, however, that might have you guessing animal, vegetable or mineral for the whole meal. But no more, since we'll learn about Jello on today's Moment of Science. Jello is a trademark name for gelatin, a food that people have enjoyed for generations. To answer the question animal, vegetable, or mineral: gelatin is an animal product. It is prepared by soaking the bones, skin, or connective tissue from pigs or cows in a bath of mild hydrochloric acid solution. After this, the animal products are heated in distilled water for many hours, and finally boiled. The fluid that collects from this process is drawn off. What's left is dried, and ground into a fine, pale yellow powder. This is unflavored gelatin, the basis of all gelatin salads, desserts, and drinks. Gelatin is valuable as a food because it is pure protein and it is easy to digest. A gelatin made from vegetable protein, called agar-agar, is made for vegetarians. When powdered gelatin is stirred into hot water and then chilled, it forms the jiggly, gelled product that we are most familiar with. This gelled product is not strictly a solid or a liquid. Technically it's a colloid: a liquid suspended in a solid framework. As the hot mixture cools off, the long strands of animal protein lock together into a solid framework, trapping tiny droplets of liquid water in the process. It's these droplets of water, trapped in a mesh of animal protein, that hold all the coloring and flavoring in your favorite gelatin dessert.
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