This course introduces a number of basic scientific principles underpinning the methodology of cooking, food preparation and the enjoyment of food. All topics covered have a strong basis in biology, chemistry, and physics application. Among others, they include the consumption of cooked food, the physiological and evolutionary implication of the senses, geographic and cultural influences on food, and the rationale behind food preparation. We will also discuss issues such as coupling of senses to improve sense stimulation; altering flavor by chemical means; and modification of the coloration to improve the appearance of dishes. Following the video demonstrations of the scientific principles of cooking, you will learn to recognize the key ingredients and their combinations for preparing good healthy food. At the end of this course, you will be able to: - appreciate the scientific basis of various recipes; - develop your own recipes by integrating some of the scientific principles into new dishes; - recognize the influence of the material world on human perception from the different senses; - appreciate the art of integrating science into cooking and dining. Important Note: This course is not designed for people with special dietary needs such as vegetarian, diabetic, and gluten-free diets. If you feel uncomfortable with any part of the assignments or activities of this course, you can substitute some of the ingredients or ask friends and family members to help with the tasting of your assignments. Alternatively, you may skip that specific assignment provided that you have fulfilled all other qualifying requirement to pass the course. Course Overview video: https://youtu.be/H5vlaR0_X2I
7.2: How can we manipulate the texture of plants?
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From the course by The Hong Kong University of Science and Technology
The Science of Gastronomy
263 ratings
From the lesson
Module 7 and Module 8
This week, we will look at how fruits and vegetables can enhance the quality in cooking and to learn about the properties of meat.
Meet the Instructors
King L. ChowProfessor
Division of Life Science
Lam Lung YeungAssociate Professor
Department of Chemistry
The content of a fruit in fact is going to change the texture a lot.
Let me demonstrate that to you. I have two kiwi fruit.
Okay, so it's here. one is ripe and the other one's not.
Let me try it out. This one Hmm.
Okay. I'm going to try to like, take some of it
out. It's not as easy.
How about the other one. Much softer.
I'm going to try to take something out. Easily I can put my spoon into it.
Now. So, what happened?
In fact for the right fruit, the texture of the fruit is quite different because
they have a lot of sugar, solution in it, and also the cell will actually, they are
much soften. So therefore, this sugary solution where
the succulent kind of like impression. We call that a very melty type of
appearance. Now, in fact, we always associate that
with fruits; such as, mango, kiwi and pear, right.
So, therefore, substance inside a particular vegetable or fruit, is going
to, in fact, change the texture. Now for example, potato juice/g.
Potato, in it, there are a lot of grainy substance in it.
That in fact, that is the starch. What happen is that if you have just a
potato, you purchase it from the market, actually they are pretty tough.
We have some potato here. Yep, pretty tough.
But you'll find that, after you have cooked them, in fact, some of these
starch granule, they become like a soft and they aggregate together and become a
little bit mushy. And of course, if you wanted to be very
like crispy also, you can prepare it into potato chips.
So, definitely, they can be of different kind of texture.
And that is depending on the starch granules in them.
So in raw vegetables these starch granules, usually they're very hard.
And so therefore when they're packed together they become very granular.
This chalkiness of, of texture that you, you sense in fact is the starch
granules. Now.
The interesting thing that as I pointed out, as you try to cook them a little
bit, at, 50 to 60 degree, you'll find that in fact, these kind of starch
granule, they will start to swell a little bit, soft water and what they
found is some sort of gel like structure. And they're gel like; therefore, they're
much softer. You don't sense the same kind of granule
and they form some sort of a sponge on sopping water.
And in a way, that give you the tenderness, or meshy type of like a
feeling. So, therefore, the change of temperature
can change the texture. Now, of course, you can continue to do
that with when you cook. initially at the wrong temperature, all
the plants or vegetables. They have their cell wall more or less
intact. But then when you raise the temperature
to 60 degree, what you have is that the cell membrane, they would be damaged, so
some of the material inside would be released.
And the cell start to lose water, and they start to deflate and become very
flaccid, and at the end, they are no longer as rigid as original.
They are, they become a little bit more chewy.
Why chewy? Because a lot of time they still have
fiber in them. But if you continue to, cook them, and
increase the temperature, or you boil them for a while, you find that well, all
these cell walls disintegrate. They are totally destroyed.
They become weakened so much that. Well, all this cement that links all the
cells together, they're broken down. So what happens?
This is something like that. It's like a puree, right?
So, ti's like a suspension of all this plant substance.
Together like a paste. Now, having that, so we wonder.
Well, what other factors can change the texture?
Would the pH of water affect the texture of fruit or even vegetables?
Let me show you something. Which is in fact a lot of these
fruits they are being bind together by some of the same manners that link them
together. And these are sometimes the
hemicelluloses, they are not very soluble in the acid condition, but however if you
change it to the alkaline condition They will start to melt away.
So let me show you something. So this is a, diagram of some vegetable,
this is it's choy sum. This choy sum we simply cook it in tap
water. I want you pay attention two thing.
One is this popular choy sum in fact is
and you pay attention to the color of the plan as well as the medium what is this
one,this one is we cooked in tap water for five minutes ,how about the next
one,the next one is like this,so you find that by the choice of stew rather to be
intact Pay attention at the medium. The medium is much lighter in color.
What happened to it? In fact, it is cooked in the vinegar for
five minute. But, how about the third one?
The third one, well, it's really like a soup.
So, you look at that. Well, the can you still
recognize what the is like? It's somewhere here and the medium is
very dark green. So what happened to it, in fact, we cook
it in baking soda for 5 minutes, so what's the difference?
Tap water, we all know that from most of the city, tap water is usually a little
bit alkaline, alright, a little bit. But if you put it in vinegar, it is a
relative acidic. That means it, as we call it, pH is much
lower. But when you put in baking soda that gets
rid of the alkaline. So I want to show all this plants to you
again and see actually how they look like.
So this one we cook it in tap water. Look at what happened.
So basically the plant is still relative intact, relatively green.
Okay. How about the next one?
This one. So this is the one that we cook it in
vinegar. You notice that it's still relatively
intact. Okay, but pay attention to the color.
The color seems to change a little bit. We're going to cover that a little bit
later. How about the third one?
This is the one that we cooked in the baking soda.
I hope that you can still recognize it. Well, this is the one which we cook in
baking soda for five minute. So basically they're so mushy that I
can't even tell that is a vegetable. And the solution the, the medium that we
use to cook it is relatively green. But even for the vegetable, it's still
green. Okay.
Now, having that in mind, we say that in fact we can use this particular property.
We can play around with it and say determine how we want to cook vegetables.
Sometimes we say, whoa, whoa, if I don't want to put it in the water or medium to
cook it, can we cook it some other way? Yes.
we can steam it, we can fry it or we can bake it, but in all these cases, what
happened? We don't have a medium surrounding this
particular vegetable. So, but remember when we cook them, this
plant is start to disintegrate. So the membrane will be broken.
And so therefore whatever inside will be released.
Remember what I said? Inside, that's the vacuole.
The vacuole usually is slightly acidic. So therefore, this acidic would come out.
So therefore, what happen is that. The acid when it comes out, it doesn't
really change anything about the or the cements that have to
glue all this together. So therefore the plant would still be
pretty good looking.Okay. Except the color.
I'm going to talk about that later. Now.
What happens, in fact we notice that the presence of some of the ions, they are
also playing a very important role in changing the texture of these plants.
For example we say that the calcium, well having the calcium there would slow the
softening of all these plants. Why is it Remember that I said that these
plants out they need to use the glue them together and what
happen is that calcium is a very essential ion to help to make this semen
work very well. So therefore it will put a lot of the
calcium there, they are going to stick together much better so that means it
stick together much better. They are not going to dissolve away.
Or to be separated or disintegrated. So what happens that when you have
calcium, they usually, they would be tougher, little bit stiffer.
On the other hand, if you add a little bit of salt, sodium chloride, table salt,
what happen is that table salt is going to compete with the calcium for the same
binding of all the cement. So, it kicks out all the calcium, so that
the association between the plant and cell become less tight and as a result
this sodium displacing the calcium ion would make the cell wall and the cement
weaker. So, therefore, what happen?
They would dissolve away much more easily.
Okay. So, adding different kind of ion makes a
difference. Now, so therefore, when we are cooking
there are things we need to pay attention to Do you want to cook it, where hard
water those you collect it from wells. Also, these would rich in calcium.
When they're rich in calcium usually when you cook the plants would stuck together,
you know, more firm appearance. or you could shorten the softening time
by adding a little bit of sodium salt. Then they would be softer much faster.
Now, so with that we also say that sometime for some of the vegetables, in
fact we would like to use approach which is called precooking.
This precooking refers to we take some of these fruits or vegetables.
We raise the temperature to 55 to 60 degree.
For a while, why do we want o do that? And we find that once you do that in
fact, those vegetables, they can stay firm for a longer time.
What happened to that? Is that in fact we notice that in the
virtue of mode they do have some enzymes. These enzymes is going to be acting to
help to glue the cells together and they would be activated only at this
temperature about like at 50 degrees. And at that temperature if these enzymes
are activated; so that means they help to glue the cells together to make them
firmer. And after they have done it, even though
you continue to cook them to a higher temperature they will be stuck togther
permanently. So therefore the firmness can be
maintained. And at the same time remember if you cook
them to 50 degrees some of these cells they would be Killed and when they're
killed, the vacuole sometimes they will release calcium and the endoplasmic
reticulum, they also release calcium. This calcium further strengthens a
sensation of all this cement. And as a result by this pre-cooking you
basically preserve the firmness of the vegetables.
Now don't forget that in fact we commonly we have also another type of plant that
when we eat them, you notice that no matter how long you cook them, they are
still very crunchy. What kind of plants are they?
These are such as the, the water chestnuts, the lotus roots, the bamboo
shoot, or so. These kind of fruits, you can cook them
for hours. They still, they are very crunchy.
So what happened to them? So they look very different, they belong
to different classes of plants. But it turns out that, again, enzymatic
reactions play a very important role. Because all these vegetables or, or, or
fruits what they have is they have something which is called phenolic
compound. Phenolic compound they are present in the
cell wall so what happen is that when these in the cell wall this phenolic
compound such as a ferulic acid they will form bonds were off the cell wall
carbohydrates, so what happen is that help to stick them together very well and
prevent them from being dissolve away So as a result when you cook them, these
kind of fruit, even though you cook them for a long time, they stay stuck together
to maintain the original texture. Now with that, essentially I tell you
about how the texture can be changed because of the pH.
Because of the various enzymatic reaction in, in them.
And also of course very importantly, it depends on what kind of vegetable you're
talking about. And you need to understand the basic
features of these fruits or vegetables.
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