Sushi is not glutinous rice, so why is it not undercooked when eaten cold?

Key points:

1. "Amylose" is easy to be stuck, while "Amylopectin" is not easy to be stuck

2 Glutinous rice is sticky but soft, non-glutinous rice is not sticky but is raw, and semi-glutinous rice is neither sticky nor raw

3 Sushi rice is a "semi-glutinous rice" that is easy to digest, but its satiety capacity is similar to that of ordinary rice.

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When rice is cooled, it tends to be hard to chew, but glutinous rice remains soft after cooling, so rice dumplings and rice cakes can be eaten even at room temperature. However, whether it is Japanese rice or sushi, they do not use sticky glutinous rice, so why is it that it does not become hard when cooled, but is elastic and smooth to the mouth?

It turns out that in addition to "glutinous" and "non-glutinous", rice also has a "semi-glutinous" type, and sushi rice belongs to this category. As for the relationship between "glutinous" and "half-cooked", we need to first understand the "classification of starch".

Rice contains more "amylopectin" and glutinous rice contains more "amylopectin". More than 70% of rice is made up of "starch", which can be divided into two categories: "amylopectin" and "amylopectin".

Ordinary rice contains more "amylopectin", while glutinous rice is mainly composed of "amylopectin". Its sticky property also comes from the high content of "amylopectin".

●The molecular structure of amylose is a straight line

● In addition to a straight main chain, amylopectin has many small branches, which are called "branched chains"

When the rice is heated, both the straight-chain and amylopectin will become loose. At this time, the rice grains will look very soft, and the digestive enzymes in the intestines can also digest the rice from the red spots.

However, when the rice is cooled, the "amylose" will be tightly arranged together and become very solid. It is difficult to chew and feels raw, and it is difficult to be digested by digestive enzymes. On the other hand, due to the obstruction of many small forks, the starch molecules of "branched starch" are difficult to be tightly arranged, and still maintain a relatively loose structure. Therefore, glutinous rice can remain soft even after it cools down.

Sushi rice is between "ordinary rice" and "glutinous rice". Now that we understand the relationship between "starch" and "undercooked", let's take a look at the characteristics of sushi rice. According to research data:

● The content of "amylose" in glutinous rice is basically below 5%

● The "amylose" content of ordinary rice is usually above 20%

● The "amylose" content of common Japanese varieties such as Koshihikari rice remains around 15%, which is between "ordinary rice" and "glutinous rice" and is called "semi-glutinous" rice.

Therefore, it can be inferred that Japanese rice used for sushi contains a high content of "branched starch". After cooling, there is still enough space between the starch molecules, so that the rice will not become "solid" and difficult to chew. However, since the content of "branched starch" does not reach the single-digit level of glutinous rice, it does not feel sticky to the touch, so from a natural sensory state, people are more inclined to think of it as the same thing as ordinary rice.

In addition, it must be mentioned that the data also shows that the "amylose" of many varieties of rice in China is also around 15%, which is very similar to sushi rice, so it should not be undercooked? Why don't I feel this way? The possible reason is that the Japanese rice varieties are very pure, but the general rice in China often mixes different types of rice, so after mixing several different varieties of rice, this characteristic will naturally not be seen!

Is sushi rice easier to digest? The answer is yes!

From the data below, we can see that "semi-glutinous" rice

● Rapidly digestible starch is between glutinous and non-glutinous rice

● Slowly digestible starch is the same as non-glutinous rice, higher than glutinous rice

● The resistant starch content is the same as glutinous rice, but lower than non-glutinous rice

In other words, "semi-glutinous" sushi rice is digested faster than ordinary rice within 20 minutes after eating, but the digestion speed is the same as that of rice between 20-120 minutes, which means that the body absorbs 10% more sugar than ordinary rice, but the feeling of fullness is similar to that of ordinary rice. Considering that it will not be undercooked, "semi-glutinous" sushi rice can completely replace ordinary rice!

References

[1] He Xiaopeng, Zhu Changlan, Liu Linglong, et al. Differences in amylopectin structure in different rice varieties and their relationship with starch physicochemical properties.