Yuan Wuxin
1 Pear, apple, banana, potato and other fruit and vegetable juices are easy to change color. Not only is it ugly after discoloration, but the taste is also affected. What shall we do? Add some lemon juice.
② How many polyphenols are contained in fruits and vegetables? After peeling, these compounds are exposed to air and oxidized to form quinone (kūn) compounds. This quinone compound can easily connect with each other and become a "brown pigment", thus discoloring these foods. Lemon juice contains a lot of "ascorbic acid", which can reduce quinone to its original polyphenol state; It can also be oxidized directly, thus consuming oxygen around polyphenols, thus protecting polyphenols from oxygen attacks. In this way, ascorbic acid sacrifices itself, protects fragile polyphenols and keeps the "fresh" colors of fruits and vegetables.
③ In the food industry, people can directly add ascorbic acid according to the mechanism of lemon juice. In fruit juice and vegetable juice sold in supermarkets, ascorbic acid is added to many wines to maintain their appearance and flavor.
④ The function of ascorbic acid is not limited to this. People often add nitrite to cooked meat products. Nitrite has two functions: first, it reacts with myoglobin to make it appear attractive red; The second is to inhibit the growth of bacteria and realize the anti-corrosion function. Adding ascorbic acid can promote the previous reaction, thus accelerating the process of "color development". Many people think that nitrite is a "carcinogen". In fact, it is not carcinogenic in itself. Nitrosamines are carcinogens only when they react with amino acids in meat. If ascorbic acid is added to meat, this transformation process will be inhibited, thus reducing the "possible" cancer risk of nitrite. Ascorbic acid is sometimes added to meat products that do not need nitrite. Because the oxidation of oil in meat will release a bad taste, which is commonly known as "spicy taste". If ascorbic acid is added, it will consume the surrounding oxygen first, thus protecting the oil from oxidation and helping to keep the meat fresh.
⑤ Ascorbic acid itself is easily oxidized to produce deoxyascorbic acid. These deoxyascorbic acids do not want to "lose their homes", but will take other people's hydrogen atoms to rebuild their homes. Taking advantage of this characteristic, people often add ascorbic acid in pasta processing to improve dough properties and increase dough gluten. Flour contains gluten, which contains a lot of sulfhydryl groups-the sulfur atom has a hydrogen atom, and deoxyascorbic acid will plunder its hydrogen atom. When we knead dough, the hydrogen atoms in sulfhydryl groups will be taken away by deoxyascorbic acid, and the remaining sulfur atoms will be connected in pairs to form so-called disulfide bonds. When a large number of disulfide bonds are formed, the gluten in the dough forms a huge network, thus strengthening its tendons.
⑥ In most cases, food additives are used to improve flavor and taste, and increase food stability. , itself has no nutritional significance. But ascorbic acid does not belong to this "majority". When used as a food additive, it is usually called "ascorbic acid". Moreover, it is also a nutrient that the human body needs-vitamin C, which is unstable. Air, light, heating and contact with metal containers will make them inactive or decompose. However, it is this instability that makes it have good "oxidation resistance". In vivo, it protects cells from oxidative damage. When it is added to food, it is oxidized at the expense of other ingredients, thus protecting other ingredients in food.
-Selected from Food and Life (with deletion)
1. What does the topic of "nutritional food additives" in this article mean? Why is there nutrition? Please specify. (4 points)
Please read paragraphs ②-④ carefully and fill in the appropriate contents on the horizontal lines below. (4 points)
The mechanism of adding (1) ascorbic acid to fruit and vegetable juice is that quinone can be reduced to its original polyphenol state; It's fine too
(2) The mechanism of adding ascorbic acid to cooked meat products containing nitrite is that it can inhibit the transformation of amino acids in nitrite-meat to nitrosamines.
3. Please talk about the meaning and function of adding words in the following sentences in the context. (4 points)
(1) If ascorbic acid is added to meat, this transformation process will be inhibited, thus reducing the "possible" cancer risk of nitrite.
(2) These deoxyascorbic acids do not want to "lose their homes", but will use other people's hydrogen atoms to rebuild their homes.
4. What is the interpretation method used in the third paragraph of this article? What's the role? (3 points)
It is generally believed that food additives are harmful to human body, and talking about "agents" will change color. After reading this article, what do you know about food additives and their use? Please talk about the content of the article. (4 points)
Answer:
1.(4 points) refers to ascorbic acid. (2 points) Ascorbic acid, that is, vitamin C, is a nutrient required by the human body. (1 min) has good antioxidant capacity and protects cells in vivo from oxidative damage. ( 1)
2.(4 points) (1) Direct oxidation consumes oxygen around polyphenols to protect polyphenols from oxygen attack; (2 points) (2) Promote the reaction between nitrite and myoglobin, and accelerate the process of "hair color". (2 points)
3.(4 points) (1) The uncertainty of "possibility" shows that nitrite itself is not carcinogenic, and only when it reacts with amino acids in meat to produce nitrosamines can it cause cancer risk. (1) reflects the accuracy of the interpretation language. ( 1)
(2) The metaphor of "failure" (1) vividly shows that ascorbic acid is easily oxidized, thus generating a substance-dehydroascorbic acid. ( 1)
4.(3 points) For example, (1 minute) specifically shows that ascorbic acid is widely used and plays a great role as a food additive. (2 points)
5.(4 points) Not all food additives are harmful, some food additives have nutritional value, and some food additives can improve flavor and taste, and increase video stability, without talking about "agent" color change. (2 points) As long as food additives are used reasonably, they are harmless to human body. (2 points) (If all food additives are harmful, no points will be deducted)