So, if you want to talk about vegetable, we need to understand actually how
vegetable are contributing to food. Now, today in this lecture we're going to
cover a bit about vegetables, plants, what their structures are.
And how they are related to textures, how they're related to taste, and how they
are affecting the appearance of the food. And we are going to talk about some of
the taste that we encounter in vegetables, such as mostly sweet, also
the bitterness. And don't forget savory, umami, the very
tasteful experience and also we are going to talk about astringency, about
attendant, that we encounter a lot of times when we are eating plants.
Now, having fruit, or vegetables in our dishes, in fact they are contributing a
very important components for our dishes. Why is that?
Think about that, when we put vegetables or fruits in a particular dish, these
vegetable usually they enrich the kind of variety of different kind of textures,
such as having mashed potatoes. They are relatively mashy and then we
have crunchy celery, we have some crispy beans so therefore there's all kind of
texture that we'll be able to generate and of course having fruits and
vegetables there are a lot of colors we can add.
Like for example where we can use the tomato a lot of time, strawberry, these
are rare, and what happen, orange, carrot, lemon, yellow.
also brocolli and all colli flour, they are given different kind of colors.
And infact, the variety of colors also is very stimulating, is very pleasing.
And of course, plant by them self, or the vegetable by them self, in fact they
offer different kind of flavor, and this flavor sometimes it would be something
that we particular want to experience. Now, let's look at how plant cells are
really like, and I want you to focus on two particular structures.
Now this is the plant cell. We talk about it probably briefly a bit
ago. that, these plant cell, in fact, they are
organized in such a way that they have a membranous body.
It's a volume with all the small particles and components in it.
But that important part of it is being surrounded by a cell wall.
The cell wall is relatively rigid to provide the kind of shape And texture
that maintain their shape. Now, going into the cell, in fact there
are two very major component. One is this big green circle.
That represents structure in the plant cell, we call them vacuole.
And basically, it's like a very watery compartment.
That it has a lot of minerals in them, a lot of pigments in them.
And also there is another part which is called endoplasmic reticulum, another
organelle inside these plant cells. In fact, both of the vacuole as well as
the endoplasmic reticulum, they are the places that they store a lot of calcium.
And later on I'll tell you how the calcium is going to make a difference in
terms of changing the texture of this particular plant cell.
Now when I talk about cell walls I said that they it's rigid.
What exactly it is. Cell wall in fact is made of some very
common component called cellulose. Or sometimes there's another one which is
called hemicellulose. Cellulose usually they are very
crystalline they are very rigid they are giving a lot of toughness to all these
cells. But when hemicelluloses is being talk
about, usually, they are much softer. They are not as organized, so therefore,
they provide relatively little strength in terms of the shape of this plant cell,
but they help to maintain some integrity of the cell.
And also, that would be pectins. These are the fibers of not much
nutritional value but we have them in the plant cells too.
Now, when we have all this structures as the outside, as like a scaffold.
Make sure that the cell is maintaining a certain shape.
That gives you that texture, strong and rigid.
But how about one plant cell and another plant cell?
They need to be coupled together. So we do have glues, and these glues, we
call them like a cement, that they are glued together.
This particular cement, in fact is very sensitive to the level of calcium that
they encounter. And finally these vacuoles, as I pointed
out, is always filled with a lot of substance, including enzymes, sugar,
acids, proteins, and you may that actually they are also very nutritional
to you. And a lot of time, this vacuole, in fact,
they make a lot of contribution to the way that the plant is going to look,
because when they break open, some of these constituents would be released, and
that would change the way the plant look or how they the texture is like.
Now, combine all together. I would say well therefore, the texture
bot is basically based on the cell wall, and we understand a little bit about
osmosis. So that is the water, and the water and
the cell wall and the membranous, compartment.
How they get to organize together. It gives you the fullness of how this
cell was like. And of course, the the presence of all
this from kind of granule, including such as the starch, they also give you a
different kind of texture. And of course, we have organelles such as
chloroplasts, green in color, chromoplast, those are colorful particles
inside these plant cells. And also pigments in the vacuole.
They contribute to the color of a, a vegetable.
And finally, within this vacuole there is a lot of compounds, that they give you a
specific flavor of this particular vegetable.
Now having that, that be, with this cell again, I say that water and cell wall,
they're very important. Why is that?
Because when the water is abundant, based on osmosis the water would always go into
the plant cell, and so basically they will fill the cell to the maximum
capacity they can hold on to. Until they reached a level the cell wall
sets the boundary that I cannot expand further, very rigid, and therefore it
creates the pressure and act on the cell wall.
And so therefore the plant is going to stand firm, so you think about that why a
plant is going to be like this. They can't stand firm like this because
the water in them that maintain that integrity and make sure that the pressure
act on all the cells that make them stand up like this.
Now, but when water is running out, and some of the water is hydrated or so.
What happens is that then the plant is going to be a little bit wilting.
Now therefore, water as well as the cell wall plays important role.
So essentially it's illustrated in such a condition, that we say this is the cell
wall. Normally, when in a condition that
water's not going in or going out, we say that is an isotonic condition.
This cell, they basically look the same normal appearance, but when you put it at
a place where there's high salt, I call it hypertonic.
Then all this waster will be drawn out because of osmosis.
Therefore, they would have a lot of the water gone, and these particular cell
wall would not be supported by all the water pressure to extend them.
So therefore they will. And how about on the other side?
If I put it in a high hypotonic solution, that means that the solute is lower than
the concentration of solute inside the cell.
Then the water would go in and the water would constantly expanding to make it
very turgid, so that they are much firm. in such a way, then we can now look at
how we can play around with this kind of like, a water content.
We can make a plant, become very, turgid by putting it in a hypotonic solution.
So therefore they will stand up. They are much harder.
But then, if you want them to be softer, what do you do?
You put some hypertonic solution outside or you put salt outside, so that it would
draw all the water out. They would be limp and wilting.
Now in that case, you can change the texture of the, the plant or the
vegetable and also sometimes, we say that for some of the plant if they have a very
large refuge, they have a, a lot of watery content of it.
and when the cell wall is not very tough what you'll have is that you simply apply
a little bit of pressure on them. Well, basically they would collapse very
easily. And that kind of feature, we call that
very melty. in a way, it's that you can imagine that
when you're eating a mango or you're eating a peach which is really ripe.
Then you'll find that you bite onto it, it's like you are biting on something
which is very soft. Now, all these are related with texture
and together, in fact, it gives you the background about what kind of
contribution prawn can give.
King L. ChowProfessor
Lam Lung YeungAssociate Professor
