问题 问答题 简答题

茶多酚各组分及与其他抗氧化剂之间存在协同作用,请说明协同作用的机理。并举例说明。

答案

参考答案:

茶多酚各组分及与其他抗氧化剂之间存在协同作用,增强了茶多酚的抗氧化效果。这一作用基于氧化还原电位的偶联氧化机理。一方面偶联作用降低了直接反应的两种物质之间的电位差,使反应易于进行;另一方面,偶联的抗氧化剂油水分配系数互为补充,在体系中合理分布,充分发挥了每一种抗氧化剂的功能。

(1)茶多酚各组分之间的协同作用

茶多酚对自由基的清除效率随儿茶素单体种类的增多而增加。组合儿茶素的增效效果,既不是单组分儿茶素的简单相加,也不是相乘作用,而是与儿茶素摩尔浓度比例呈高度正相关。

(2)茶多酚与维生素E的协同作用

当两种物质同时加入时,氢过氧化物的生成受到抑制,诱导期显著延长。

(3)茶多酚与维生素C的协同作用

当茶多酚与维生素C组合时,维生素C可以通过捕获过氧自由基,阻断链反应而抑制氧化;另外维生素C具有极强的还原性,可使油脂中的氧浓度降低。

(4)茶多酚与ß-胡萝卜素的协同作用

茶多酚能防止亚油酸体系中的ß-胡萝卜素的氧化,原因是茶多酚抑制了ß-胡萝卜素的氧化分解,提高了体系中ß-胡萝卜素的保存率。

(5)茶多酚与脂溶性茶多酚的协同作用

茶多酚与脂溶性茶多酚能显著降低脂质的过氧化值。在乳化体系中茶多酚与脂溶性茶多酚联合使用的抗氧化作用明显高于单独使用。原因是抗氧化剂可以更加均匀地分布于乳化体系中,提高抗氧化作用。

阅读理解

Have you ever done something foolish and it made you feel so embarrassed(尴尬的)?

Well, that’s exactly how I felt. On a Saturday morning last autumn.I went to town to do some shopping and as I was on my way home from the shop,it suddenly began to rain. I at once ran into a nearby phone box because I didn’t have an umbrella.It was raining so heavily that I had to stay in the phone box until it stopped.

A few moments later,I saw a young man walk up to the phone box,wearing a yellow raincoat and holding a box. I didn’t want to go out into the rain,so I picked up the phone and pretended(假装) I was talking to someone. I thought the man would go away,but he didn’t. He just waited in the pouring rain,and I acted as if I was deep in conversation.

Luckily,the rain stopped after about ten minutes.“Okay,Mum,” I said loudly into the phone,“I’ll see you later. Bye!” I put the phone down, picked up my shopping bag and walked out of the phone box. “I’m sorry I took so long.” I said to the man.

“Oh, I don’t want to use the phone,” he answered, smiling.“I’ve just come to repair it. There is something wrong with it, you see .” I felt myself go red in the face and I hurried away with my head down,feeling a complete fool. That was certainly one of the most embarrassing moments of my life! 

小题1:Why did the writer go to the phone box and stay there?

A.Because she wanted to keep warm.

B.Because she wanted to wait for her friend there.

C.Because she wanted to phone her mother.

D.Because it rained heavily and she had no umbrella with her.小题2:The writer thought that the young man wanted          .

A.to repair the phone.

B.to use the phone.

C.to stay in the phone box.

D.to clean the phone box.小题3:How long did the man wait for?

A.About five minutes.

B.About fifteen minutes.

C.About ten minutes.

D.About thirty minutes.小题4:Which of the following is TRUE?

A.The story happened on a cold Saturday morning last summer.

B.The writer telephoned her mother.

C.The writer was on her way home after doing some shopping,suddenly it began to rain.

D.The writer knew why the man came here.小题5:Why was the writer embarrassed?

A. Because she did something foolish.

B. Because she got all wet.

C. Because she made the young man wait so long. 

D Because she couldn't get out of the phone box.

单项选择题