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Good morning everyone. How are you this morning? Good. Let's continue to explore and learn
more about gelatinization. For gelatinization to occur, what is the main thing that we must
have? Water. So gelatinization is also known as
water mediated process. Without water, you do not get gelatinization.
If you heat the dry starch, the dry starch contains around maybe about 10-12% of moisture.
With that amount of moisture, water content, if you heat the starch, what will happen?
Dry powder, 12% moisture. If you heat up, what would happen??Will it gelatinize? Because
the glass transition is actually above the room temperature. So if you heat up the dry
starch powder, when you increase the temperature, you don't not see a proper gelatinization.
Probably you might see the starch gets burned. It will start to decompose which is burn.
It will start to decompose. It will just burn. So we need Some amount of water. So when we
talk about gelatinization, we always look whether gelatinization occurs in the presence
of excess water or limited water. When we say excess water, it means that the water
content is above 60%. So that is roughly about the amount of water for gelatinization to
occur. So in the presence of excess water, above 60%, and we increase the temperature
above the gelatinization temperature of the starch, and we allow sufficient time, the
starch would gelatinize completely. Cook completely. How do we know? In the previous lecture, we
have said that when we look under the microscope, there is no more Maltese cross. Or when we
look under the DSC instrument, we can see the peak from the onset to the end. So we
can see the whole peak. So that is how we can determine complete gelatinization. So
in order to get complete gelatinization, we need to have above 60% of water. We heat it above the gelatinization
temperature and give it sufficient time. It is a combination of temperature, time and
water. What happens if the moisture content is less than 60%? Can we get complete gelatinization?
We have to cook at higher temperature and a longer time. But if the moisture content
is even lower. So maybe if you use a higher temperature and a long time, we might still
not get complete gelatinization. If we do not get complete gelatinization? How do we
know? Well, maybe we can take some samples and look under the microscope. If you get
complete gelatinization, all the starch granules will be disrupted, burst. Because it will
swell to the maximum and finally it will burst. So when you look under the microscope, you
would not see the granular structure anymore. So that is one indication that it has complete
gelatinization. But when you get incomplete gelatinization, when you look under the microscope,
you might see some form of granular structure. But maybe not in the proper shape. Maybe it
has already been deformed. But still you can see Some kind of granular structure. And sometimes
the term that we use in starch science, we use a term to describe the distorted granular
structure, we use the term ghost. Ghost granule. We call it ghost granule. Because it comes
in all form of scary shapes. So that is one way. We looked under the microscope, you can
see deformed granular structure or even ghost granular structure. When we carry out gelatinization
below 60%, then we can say that this type of gelatinization happens under limited amount
of water. So we would not get complete gelatinization and will give different properties to the
product. And now this slide, I'm going to talk about
the mechanism. Because now that we have excess moisture, water and limited water and moisture,
the mechanism will also be different. Remember that we start with a granule in the native
form. We now know that the starch granules are in the semi-crystalline form. It has about
30-40% crystalline phase in the granule. So now we add water and increase the temperature.
The amylopectin molecules in the granules form the crystalline phase. Where else, the
amylase in the native granule forms the amorphous phase. So there is two different domains and
phase. Crystalline which are mainly amylopectin and the amylose?
And now, we add water. The granule will absorb water. We will increase the temperature. So
let's say in the excess moisture condition where we have more than 60% water. So initially,
when the granule absorbs excess water, the amorphous region, domain or phase in the granule.
Amorphous is where the molecule is random and have a quite loose structure. Unlike crystalline.
Crystal, the molecules and the atoms are arranged very close together. Compact. So it is more
difficulty for the crystalline phase to absorb water and molecules easily. But the amorphous
is more kind of loose and less compact, So water can sort of be absorbed easier. So the
amorphous phase absorbs water and this has the effect to swell the granule. And as a
consequence of swelling in the amorphous region the granule will start to destabilize the
crystalline region. Because remerge that they are intermingle. They are alternate layers
between the coralline lamella and the amorphous lamella and the bark region. The bark region,
is now being destabilized because it absorbs water. And the granule now starts to swell.
The next sequence of event is that it will now destabilize the crystalline region. The
crystalline region now will start to melt provided if we continue to supply heat for
a sufficiently long time. This is only one of the mechanisms which are proposed by the
scientist to explain the process of gelatinization in excess water. But not every scientist aggrees
with this mechanism. So therefore when you read a book or any articles about the mechanism
in starch for gelatinization, you might find some differences. But let us settle for this
mechanism for our purpose. So this is in excess water. So how the mechanism will differ in
limited moisture/water? Less than 60%. This slide actually explains the limited moisture
or water content. If you want less water or you want a very low content, maybe about20-30%.
Now days, lower amount of water would not be enough to destabilize the amorphous phase.
So what would happen? At low moisture content, we need a higher temperature and longer heating
time. So that when we supply enough energy, it will be enough. Because this crystalline
phase now will require a higher amount of energy to melt the crystals. That is why when
we have less than 60% water, we cannot use the same amount of time and same temperature.
The cooking time and temperature will have to change in order to achieve the same level
of gelatinization. But in a real food system is not that simple. In a real food system,
we have starch water and other ingredients. This other ingredients will complicate the
mechanism. When we have sugar. When we have fat. When we have salt and other components.
So, for example if we add sugar. The sugar molecules themselves are very hydrophilic.
They also will bind with water. So now the sugar will compete with the water molecules
with starch. And because sugar is a smaller molecules, they will be able to bind better
with the molecules. Because starch is initially in the granular form. So the water will probably
have to penetrate the granule before it can be absorb into the amorphous granule. The
amorphous region of the granule. But now we have sugar in the Solution. And the sugar
is more free and open in the solution. The sugar now is in the free form, and they are
free, more open to the granule structure. So they will bind water easily and faster
than the granule. So more water will be bound by the sugar. And now less water will be available
for the starch granule. So in this situation, when we add more sugar, less water will be
available for the starch. So the mechanism now would be the mechanism of low moisture
gelatinization will operate. Will dominate. It will involve some destabilization of the
amorphous even in the limited moisture. But then we would need to increase the temperature.
We need to allow a longer time. We need to allow longer time. But if the moisture content
is very low, then this process cannot be completed. So we cannot destabilize the amorphous region
completely and therefore we cannot melt the amylopectin region completely. So we do not
get complete gelatinization. We do not get full swelling of the granule. So if the granule
does not swell fully, then most likely it might also not rupture fully. We will see
some pictures to show clearly the difference in the low moisture and high moisture system
or the low and high water system. Excess water, think of a product where we have a lot of
water. Porridge, soup like Campbell Soup in a can. Those are excess moisture. Limited
moisture or limited water? Crackers, very low moisture. Yes. Bread, candy. I find in
the exams or test, students will give examples. When I look in the examples, they answer candy.
But what kind of candy. Soft candy. Yes there is starch. But sometimes they give product
like, where there is no starch inside. So when you give examples, please give appropriate
answers. Something like bread and cookies, those contain starch. But these are good example
for low moisture, limited moisture or limited water product. So in those product, like for
bread, if you take a sample and look under the microspore, surely you will definitely
see some granular structure. Because in bread the amount of water is limited. Even if you
put in the oven at 2000C, still you do not get complete gelatinization.
So the theory here is based on so called water mediated. The process here is ,the medium
here is the water. So this is real data from the experiment from
this paper. So you can download this paper from Science Direct, volume 36. This s the
page number, 1998. This very cleary demonstrates the difference between waxy maize. Waxy maize
is high in amylopectin. Potato has about 25% amylose and 75% amylopectin. Hylon VII. This
is a specific name for special hybrid of a high amylose maize starch. Hylon VII is a
special hybrid for high amylose maize starch. Corn. So high amylopectin, high amylose and
normal. The starch in the middle. A very beautiful picture to illustrate the gelatinization process
and the effect of the amylose and amylopectin ratio. This is without heating and at room
temperature. So you can see this is the original granular structure. The original before heating.
Now we heat it to 400C. 400C is usually still slightly below the onset of gelatinization
for most types of starch. Usually most starch will start to swell and gelatinize. And the
onset is probably about 600C and above. So 400C is approaching, approaching. bBt not
yet. But we can see for waxy maize, which contains high amylopectin, it has already
started to swell a bit. But normal strarch, potato, compare. Maybe a little bit. Hylon,
you do not see much difference. Meaning that is still is like the initial size. So this
is high amylose. We now heat to 700C. S700C is probably above or already above past the
onset of gelatinization. So we can see the waxy maize granule, has already burst. We
do not see a proper granular form. Potato, at this temperature, has probably reached
the maximum swelling just like a balloon. If you blow a little bit more, it will burst.
How about hylon? Probably a little, little bit, maybe about 10% swelling. Or you cannot
tell from the picture. But if its swell, at most it will be about 10-20%. At 1000C, it
is well above the gelatinization temperature for most starches. As you can see waxy maize,
this even at a higher magnification actually. You can see it has fully burst. Potato has
already burst. But hylon, you can see some swelling, but it still has a long way to go.
So, picture tells a thousand stories. So can you tell a thousand stories? Well maybe a
few. What can we say now? What can we conclude form this picture? Anyone? Anyone? Volunteer?
Volunteer? Shikin? Louder Shikin? Need higher temperature. Higher temperature. Okay. Or
if we put it the other way round. If we expose the starch samples to the same temperature,
then we can say that the waxy maize will swell the fastest compared to the normal potato
and hylon VII. So that is probably only point we can make. We can also see that hylon VII
appears to be the least. Swelled the least. In terms of swelling capacity and the extent
of swelling of the granule, Hylon VII actually swelled the least or showed the least swelling.
The lowest. So how do we relate now, to the ratio or to the amount of amylose and amylopectin
here? So we can say that hylon VII contains the highest amount of amylose would show the
lowest tendency to swell compared to waxy maize which contains a high amount of amylopectin.
So we can say that if we have high amount of amylose in the granule, the reason why
it cannot swell faster compared to potato and waxy maize. Because the amylose actually
gives strength to the granule. It holds the structure of the granules and it will provide
and reinforce the granule. So it will become more difficult for the granule to swell. So
if you want high amylose to swell, you would need to supply enough heat. You would need
to increase the temperature, Sometimes above 1000C. So you have to heat it up under pressure.
Maybe under an autoclave. So you have to use an autoclave or a high pressure cooker So
that you can fully gelatinize the amylose starch. If you use a normal atmospheric cooking,
1000C maximum, then maybe you would want to extend the cooking time much longer. In order
to reach a full gelatinization and you must have enough water, more than 60%. But for
waxy maize, it is very easy to cook. So any starch which contains a high a high amylopectin,
it is easier to cook, because it can swell faster. But then, when the granule reaches
the maximum swelling, it will reach the maximum swelling faster compared to normal and amylose
starch, But the granule is still also very fragile. So it can swell very fast and the
viscosity will increase very fast. But then, the granule will break up and will lose its
viscosity very fast. So the curve will be something like very steep. Where else, potato,
a normal starch will increase the viscosity rather slowly, gradually. Then it reach the
maximum. And the granule will start to break, disintegrate and would lose the viscosity
but rather slowly and more gradually compared to waxy Maize. And maybe for this one, you
would not see an increase in viscosity. When the granules swell, there are few thinng actually
happens. When we add iodine, only the amylose component will bind the iodine and will give
a dark blue color. Where else amylopectin will show a more purplish-brownish color. So we can
differentiate where is amylose and amylopectin in the granule during gelatinization. So initially,
you can see like this, really dark. But, when the starch granules start to rupture,
you can see the continuous phase here, is blue in color. Which means that we have amylose
has leached out from the granule into the surrounding continuous phase? Where else,
amylopectin, the purplish in color, that is the amylopectin component which apparently
still remains in the granule because they are big molecules. And they cannot easily,
leach out from the granule. But amylose being a linear molecule, especially the short chain
amylose can leach out into the surrounding. So what we have now is a starch paste containing
the amylose and amylopectin. And maybe some granular structure. This is what we refer
to as starch ghost. The ghost granule. Now we can follow the changes during gelatinization
by looking under the microscope, or by looking at the Maltese cross. But we can also see
the manifestation of gelatinization. How it manifest physically. So one of the physical
changes during gelatinization is the increase in viscosity. So we can measure the increase
in viscosity by using an instrument like RVA. So we can measure the viscosity increase during
the process and is quite easy to do. Farahana has experience using visco amylograph or RVA.
RVA, rapid visco analyzer. So we can measure the viscosity increase during this process.
It is quite easy to do. So this graph start forms 550C, if we plot
it to start from room temperature, it will be a flat line. So when we start with 550C,
the granule starts to swell a little bit. And this is the temperature. Usually the instrument
can be programmed to heat at a constant heating rate. Maybe a few degrees per minute. Then,
usually we heat up to 950C. Ooops. Lee hoon. You are sleepy? So, the
temperature program usually will start from room temperature, or maybe around 400C. If
you know the onset of gelatinization is around 500C. We can start maybe around 400C. We do
not have to start from room temperature. Otherwise we would have to wait quite long. And then
this is the onset. Onset means the curve has an inflection where it starts to regress.
That is the inflection point. We can draw a tangent. And the intersect. The tangent
will give you the onset of gelatinization. So at this point, the granules will start
to swell a bit. And maybe we don't get the amylose to leach out yet. When we increase
a little bit more, we can see shorter amylose chains been diffusing out. And more and more.
And until, the granules reach the maximum swelling capacity. And now, this is at the
weakest or the most fragile moment of the life of the granule. Just like human beings,
our weakest moments are when you are emotionally fragile. That is the time, if the person is
not strong, they can jump off the Penang Bridge. Be careful. And here, you can see most of
the amylose has already leached/ diffuse out of the granule. In the previous slide you
can see the separation of the amylose and amylopectin, when iodine is placed. Then it
will burst and form fragments. How fast they would reach this point, would depend on the
amount of heat. The rate of heating, the sheer and also the types of ingredients we have
in the system. If we have a lot of fat, it will give Some kind of protective effect one
the granule. Kind of like a lubrication effect also. So it won't get fragmented easily. So
all of this will delay the changes in the viscosity. We can do actually an experiment
to see. So it can decrease in viscosity and form more and more fragments. So now at this
point, we have a starch paste. And the starch paste always contains a mixture of amylose
and amylopectin in the Sol plus the granule fragments. Plus the granule fragments. That
is a starch paste. That is why, the whole process is called pasting. Pasting. Or in
Bahasa'pempesan'. So if you feel it is a bit funny to say 'pempesan', than you can say
pasting. So until 950C. And the programme will start at 950C. And usually we will hold.
There is a holding period at 95 for about 5 minutes or Sometimes 15 minutes. And we
continue to monitor the viscosity changes. 95 C is fixed, but we continue to heat for
another 5 minutes, 10 or 15 minutes. And we can see now if the viscosity will continue
to decrease or it just sort of maintain. So this is one way, we can see the stability
of the starch in terms of the ability of the starch to maintain the viscosity. So this
is called the shear stability, because we continue to shear the sample. So we can compare
one starch to another in term of, what will be the final viscosity at high temperature?
So from there, you can see what is the suitable starch you would want to use, If you want
to get this kind of viscosity in the product. When you continue to heat, more and more of
the starch fragments will become smaller and smaller. And this actually will change the
rheological properties and the viscosity of the starch paste. If you heat for a longer
time and at a higher temperature. For example in the retort, you can even get some of the
amylose and amylopectin to start to degrade, break down. The long chain of the amylose
and amylopectin can start to break down or depolymerize to be a short chain. So from
a big polymer, it becomes a smaller chain. High molecular weight becomes a lower molecular
weight. And if this happens, you will get the viscosity to be reduced even more. So
this is all about the stability of starch during cooking, And will define the final
viscosity that you will get in the product. So this is a type of instruments in the old
days. This is very famous. This can be found in old flour mills or old bakery. You can
find this instrument and is called Brabender amylograph. And it is usually made in Germany.
German manufacture. So you have the bowl here, where you prepare the starch slurry and put
in the bowl. Then you have a heating mechanism. Then you have the paddle or the mixer. This
is to rotate the paddle, So that we can measure the top. So from the top, we translate that
into the shear stress. Then you can calculate the viscosity. When we use this instrument,
the viscosity is expressed as Brabender unit or RVA unit or we can also change to the proper
SI unit, centipoise. So the curve that you saw just now, the plot of the viscosity against
temperature and time, is known as pasting curve. Pasting curve.
So what can we get from the pasting curve? This is how it looks like. Viscosity against
time and temperature. The red line represents the heating program. The temperature program.
So we start by increasing the temperature linearly. Linearly. So we fix the heating
rate, then we reach the temperature to about 950C. Then we hold. This holding time can
be in minutes, a few minutes. As long as 15 minutes to see the stability of the starch.
Whether the viscosity will increase further or decrease. Then we cool down. So we always
have heating up, holding, cooling down. During the heating up, we want to see the gelatinization
characteristics of the starch. During the holding, we want to see the stability characteristics
of the starch. Stability here means, can it hold the viscosity. Hold the viscosity means,
that whatever viscosity it has reached whether it can maintain the viscosity or drop. It
will never increase. It will drop. And the cooling period now, is to look at retrogradation.
So in one pasting study, we can look at gelatinization, retrogradation and the viscosity stability
of the starch. It usually involves shearing. Phaik Hoon? Anything not clear? Pasting involves
the whole event from here up to here. During the holding period. And during the process,
the process forms the onset of swelling, till the starch loses it viscosity when the granules
start to burst. The viscosity will start to drop. So the whole event is called pasting.
Usually when we say pasting, it will also involve some form of shear that would assist
the gelatinization process. When we say gelatinization, it will involve the sequence of events starting
from absorption of water, the granules start to swell, and the amylose starts to diffuse
out from the granule. It will reach the maximum viscosity. Then the granule will start to
burst. So the whole event is called gelatinization. Pasting is the whole event which includes
the temperature, the sheer we pour into the system. In order to form a starch paste, the
starch has to undergo the process of gelatinization. I know some books, differentiate between pasting
and gelatinization. But it actually involves both. Gelatinization must take place in order
to achieve the pasting, to paste the starch. The starch paste consists of the amylose and
amylopectin plus the fragmented granule. So in order to get all this, the starch has to
undergo complete gelatinization. And the temperature of gelatinization is not a single value, or
a single temperature. But a range of temperature. It starts from here, to the maximum, till
it reaches the maximum swelling, So it will reach the maximum viscosity her. So the range
will be from this temperature to that temperature. All this are range. If we give a single value,
we refer to the onset. If we say that the gelatinization temperature of potato starch
is about 600C. This means that the onset is 600C. But it is usually better to give the
whole range from 60-650C or from 60-70 0C. So we can say at 700C, the potato starch has
reached its maximum swelling capacity. Beyond that temperature, we know that the granule
will start to disintegrate or to rupture or to burst. And it will start to lose the viscosity.
So the whole event of pasting, starting from the onset here. Here is the hot paste viscosity,
Hot paste because we are holding at 950C. So this is also known as hot paste viscosity.
So the whole thing here, we have the starch paste. So when we cool down, the viscosity
will start to increase aging. From this point onwards, that is the process of retrogradation.
Or in this case, we call it setback. So the next graphs will show you the various
parameters that categorize the gelatinization. That categorizes the pasting as well as the
retrogradation part. S during the holding period, we can measure the peak viscosity
at this point. This is called through viscosity. And the breakdown will give you a measure
of the stability of the starch. I will say more about this graph in the next lecture.
So we will stop here. The viscosity of the starch is contributed both by amylose. Both.
The swelling of other granule, the amylose which leach out to the surrounding and the
granule itself. Whether the swollen granule or the fragmented granule also. Everything
will contribute to the viscosity of the paste.