2 days, 10 hours ago

It's a great way to open this question! 

The words "Chemistry" and "mixture" in the title have perfectly pointed out the direction of the problem, and the rest is to fill in the hole. Let me fill in the hole. 

 mixture 

Cooking oil is a mixture. 

Soybean oil, rapeseed oil, peanut oil.... 

All oils are mixtures. 

The question is, what kind of mixture is it? 

This has to be seen from a chemical point of view. 

 chemistry

 
 
 95% of the ingredients in edible oil are chemically called esters. 

The remaining 5% are vitamins, pigments and so on. 

The amount of pigment, so that the color of oil. The presence of phospholipids will also increase a little turbidity. The type and amount of vitamins can not be seen from the appearance, which has a great impact on the nutritional value of edible oil. 

This is the first concept of mixtures, which means that edible oil is a mixture of these substances. 

At this level, we can not distinguish dozens of oils and fats. The secret lies in the next concept of the mixture: esters. 

 ester 

The main component of all edible oils is chemically called "ester.". 


 
 
 esters are composed of glycerol and fatty acids. Glycerin has three positions on the molecule, and fatty acids can sit in these three positions. 


 
 
 these three positions are numbered. If the same fatty acid sits at different positions, the properties of the ester are different, and the ester is not the original ester. 

There are more than 800 kinds of fatty acids. Fortunately, there are only 20 kinds of fatty acids in our edible oil. 

But think about it, even if it's only 20 fatty acids, sitting in three different positions. Using our high school knowledge of permutation and combination to calculate, the total number is also a large amount. 

 fatty acids 

All living things on earth are carbon based life, that is, the basic skeleton of biological molecules is connected by carbon atoms. A fatty acid is a chain of carbon chains, but its end is - COOH. 


 
 
 20 kinds of fatty acids are different in the number of carbon atoms in the carbon chain. 

Less than 6 carbon atoms are short chain fatty acids; 6 to 12 are medium chain fatty acids; more than 12 are long chain fatty acids. 

 
 short chain fatty acids are easy to volatilize, and many flavors are produced by short chain fatty acids. 

According to the research, the metabolic mode of medium chain fatty acids is different from other fatty acids, and the influence on body weight and blood lipid is also different. Some animal experiments showed that medium chain fatty acids could reduce the body fat weight of rats. A lot of weight-loss products are marketing with this point. 

Most vegetable oils contain long-chain fatty acids. 
The carbon atom in the carbon chain has four hands


 
 
 and the left and right carbon atom handles occupy two, and the remaining two hands have two cases. 

 
 connect two hydrogen atoms, fill up the four hands, and the carbon atoms in the whole carbon chain do so. So this fatty acid is called saturated fatty acid



 
 
 
 the two adjacent carbon atoms have a very good relationship. They pull each other with two hands. This fat is called "unsaturated fatty acid". There are only one pair of carbon atoms in a carbon chain that do this, called monounsaturated fatty acids. Two or more pairs do this, called polyunsaturated fatty acids. 



 
 
 in fact, the friendship between carbon atoms pulled by two hands is not as stable as that of hydrogen atoms. It is especially easy to be broken by a third party, such as oxygen atoms, which is called "oxidation". After oxidation, the two carbon atoms split and the carbon chain "breaks.". After the carbon chain of the fatty acid is broken, it becomes something else and gives off a strange smell. The edible oil will also be bad and deteriorated. 

The advantage is that these unsaturated fatty acids are easy to digest and absorb due to the instability of the carbon atom relationship. 

From the point of view of nutrition, this kind of unsaturated fatty acids will not be created by the human body itself. They are also necessary for human health, so people must take these unsaturated fatty acids from the outside food. 

 
 vegetable oils and fatty acids
Different vegetable oils are esters that combine different fatty acids. In other words, esters with different fatty acid structures produce different kinds of oils. 


 edible oil is an ester composed of different types of fatty acids, mixed with pigments, phospholipids, vitamins and other substances. 


Make a picture of the fatty acid composition of various oils. 


 
 
 lauric acid, myristic acid in the first column on the left... These are the common names given to these different fatty acids by pioneers in edible oil research. 

"C18:1 oleic acid" in the penultimate line means that the fatty acid has 18 carbon atoms and 1 unsaturated position. In soybean oil, oleic acid content is about 24%, and peanut oil is about 43%. 

The linoleic acid in the next row has two unsaturated sites. And then the linolenic acid, there are three unsaturated sites. 

It can be seen from the table that the fatty acid types of several common vegetable oils are similar, 
 the difference is that the proportion of fatty acids contained in them is different 
. 

In this way, because the price is ordinary and many people look down on soybean oil, in fact, it is not weak at all in nutrition. 

Understand the truth behind it, do you know how to choose oil? 

Yes, in exchange. 

The most nutritious unsaturated fatty acids, easy to oxidize and afraid of heat. Therefore, do not cook too hot, time not too long, or the nutrition will run away. 

 referencesOil chemistry, edited by Wang Xingguo and Jin qingzhe, China Light Industry Press

Bailey oil chemistry and Technology (6th Edition), translated by Wang Xingguo and Jin qingzhe, China Light Industry Press

Zhang Yuehong, et al. Effects of medium and long chain fatty acid edible oil on blood lipid and low density lipoprotein cholesterol in overweight and Hypertriglyceride patients, Chinese Journal of food, 2010, issue 2, 8, 20-27

Jing Hongjiang, et al. Effects of medium and long chain fatty acid edible oil on body fat in patients with different degrees of hypertriglyceridemia, prevention and control of chronic diseases in China, 2009, issue 2, 3, 130-132

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