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Good morning students. Any questions that you would like to ask from the previous lecture?
Anything that you need clarification or if there is any confusion, before I proceed with
our discussion about gelatinization We are still discussing gelatinization. And today
we will be discussing some of the factors which can affect gelatinization. Then after
that we will move on to discuss about retrogradation. In enmodule, I have shared a link to some
of the online presentation from the industry. As much as possible, please watch those industry
presentations. They are experts. So when they talked about modified starch. Recently I think
I shared about modified starch 101. Those are given by the experts from the industry.
They are the experts. I'm not the expert. Maybe a less expert. So I would encourage
you to watch those presentations. And if possible, if you can find time, please do a summary.
And if you feel like sharing, Share on enmodule. So no questions? Good. Also I take it that
you understand. Everything. As far as the gelatinization process is concern, there are
many factors which can affect the process. The properties of the starch itself, the processing
conditions that we use, and the types of ingredients we use. That we add as is part of the food
formulation to make the food product. So that is all the things that can affect the gelatinization
process. When I say affecting gelatinization, what I mean here is the extent, how fast and
how much. In some conditions, we want the starch to just cook or gelatinize sufficiently.
In some cases, we do not want the starch to overcook, because when you overcook the starch,
you might get some under effects. In some cases, you might undercook the starch. Meaning
that you do not get complete gelatinization. So if you do not get complete gelatinization,
but in the actual product you want a certain level of gelatinization. So later you might
have problems with the quality of the product. So this are the things that you need to understand.
If you look at this diagram. This is actually a schematic presentation of the microstructure
of potato starch dispersions in relation to viscosity and iodine binding capacity. Iodide
would bind to the amylose component to form the blue color. For amylopectin, the color
is not dark blue, but it is purplish-brownish color. So we can actually measure the binding
of done to starch by using titration. Or by using spectroscopy method to see the changes
in the blue color. So you can measure using visible spectrophotometer, in the visible
range. And you can measure the absorbance and so on. So by using this technique, we
can monitor the changes in the iodine binding capacity of the starch, for the whole duration
of the gelatinization process. And we can plot the graph like this. And at the same
time, we can also measure the changes of the viscosity. So in this graph we can measure
two things here, one is the iodine binding capacity. And the other one is the changes
in the viscosity as a function of the heating program. And we can measure the changes in
the viscosity. We measure it using the SI unit here. Pas rather than the RVA unit. Then
we measure the iodine binding capacity. And of coz we can also look under the microscope,
as from the previous lecture. I think we have seen this. The changes in the discrete, native
granule before cooking. And then it starts to swell, and deform then break up and get
disrupted. And finally form a homogenous colloidal solution. But in this form, we have the ghost
granule or the deformed granule. So we can see here the extent of gelatinization during
the pasting process can be very different in terms of how much shear we put in, how
long is the cooking time, how long is the holding time , the temperature. Whether we
cook under the atmospheric pressure or we cook under elevated pressure like in an autoclave
or in the retort. So this will determine whether we will get this, this, this or that. So if
we measure the iodine binding capacity, at each of this stage, you will see that it will
show a trend like that. Increase, then after that more or less plateau. At the same time,
you can see the viscosity starts to decrease. I think we can explain this quite easily.
Initially, the viscosity starts to increase because the granules swell. And the viscosity
of the continuous phase also increases, because we have the short fragments or short chain
of linear amylose to leach out. It will increase the viscosity of the continuous phase. At
the same time, the granules swell. So both effects will increase the viscosity. Up to
a certain point Until the granules start to break up and rupture. Just like a balloon.
And now, most if not all of the amylose will leech out and form as part of the continuous
phase. So the viscosity will increase up to a certain point and then will continue to
decrease. Iodide binding on the other hand will initially increase because the amylose
component, especially those which have leached out from the granule. Will bind with the iodine
and give the blue color. When more and more amylose start to leach out from the granule.
When more and more start to rupture or break, it will then increase. But most of the amylose
when it has been leached out from the granule. There will be no more amylose, or all the
amylose has formed complex with the iodide. So we do not expect a further increase in
the blue color. So the point I'm trying to say from this slide is, we can actually monitor
the changes in the viscosity and other changes in the functional parameters by using this
kind of experiment. So when we, come across a new type of starch, where we do not know
these properties very much, we can carry out this experiments to categorize the starch.
Especially if there is limited information regarding this? Another way to categorize
the gelatinization of starch and perhaps the more popular method which we can use and is
also very convenient and very easy to use is by using DSC. Differential scanning calorimeter.
I am sure you have heard of IMG204 about DSC. I'm not sure if you have had experience in
using it. Maybe part of your final year project, you might get to use. But DSC is actually
a very convenient way to monitor gelatinization. RVA is one. But in RVA, we monitor the changes
in viscosity. In DSC, we monitor the thermal changes associated with the endothermic change
in gelatinization. When the starch gelatinizes, it is endothermic. It will absorb heat. Because
heat is required to break up the hydrogen bonds between the amylose and amylopectin
granules. So heat is required to break up the hydrogen bond. So the process is endothermic.
And we can capture this endothermic event, by using DSC. And it will show in in a form
of peaks. This is very nice, because it is very sharp. But Usually we do not get it to
be very sharp. This to me is very sharp. I'm not sure if it is a real data or it is just
a schematic. It's quite unusual to get a sharp peak like this. If you have a pure crystal,
and you put it into the DSC. Pure crystals, means 100% crystals. And then you heat it
up above the melting point of the crystal, you will usually get a sharp peak like this.
Because pure crystal has a sharp melting point. Because pure crystal would melt more or less
at the same time. Of coz you do not hear the sound like that. But it will melt, just like
LEGO. We have a structure, and you do something to collapse it. If you have 100% crystals,
then you will get a very sharp peak. Remember starch is semi-crystalline. About 30-40% crystalline
phase. The amylopectin component in starch contributes to that. And also the crystals
in starch, the A pattern, B pattern. It is not really a perfect petrel. They have their
own instabilities. SO when they melt, they don't melt immediately. It will take some
time. So the least stable crystals will melt first, followed by the more stable crystals.
That's why in the DSC of starch. You will see something like this, more broad. In fact
when you carry out DSC for different kinds of starch, you will see the broadness or the
narrowness and the broadness of the endothermic peak is different. That will tell you something
about the nature of the crystallite of the starch. If you get a sharper peak, the starch
has a more homogenous structure. Because they melt at a narrow range. If it's broader, they
met at a broader, range. That gives us some information about the starch when we do comparison.
So what you see here, when we carry out gelatinization in excess water (more than 60%)? So in the
DSC, we have a small sample pan. Very small. Very small. You have to handle with care and
are made out of aluminum. There are two parts. The bowl and the lid. Each one, the bowl itself
the bottom part cost about RM250. and the lid costs about RM250. Sorry, it is about
RM10-15 each. So one sample pan when you run the analysis will cost about rm25-30. So it
is expensive. So when you put the sample in the sample pan, it is a really small sample.
About 5mg, then you add water. In excess water in DSC, we add one part of solid starch and
three parts of water. That is excess water. Under this condition you will get complete
gelatinization, if you heat the starch above the gelatinization temperature. And you will
get this kind of peak. A single peak. But maybe not this sharp but it is a single peak.
The scientist has given the name of these peaks as G endotherm. G endotherm. So when
you read the books, and you come across this term. and you come across the G and the M
endotherm. The G endotherm refers to a single peak. When starch is gelatinized under excess
water. So what happens now, instead Of three, to one, we reverse it one part of water and
three parts of starch. So we have a situation whereby gelatinization happens under limited
water. So in limited water, we will get this kind of peak in the DSC. There is one endotherm
here another endotherm there and is more broad. The second endotherm is called the N endotherm.
And this will occur at a higher temperature. So we call it as G+M. if we reduce the amount
of after even more, just almost like dry but not so dry to make it even more limited moisture
or water. You will get something like this. Even broader and has shifted to a higher temperature.
So what this means is that if the amount of water is less, the less amount of water, the
higher the temperature is needed to achieve complete gelatinization. The range for gelatinization
temperatures would be shifted to a higher temperature, when gelatinization is done under
limited amount of water. This is an important fact. Less amount of water, a higher temperature
is needed to cook the starch completely. And thereof knowing this, maybe you would want
to prolong the cooking time if you want to achieve complete gelatinization. Or we can,
either than prolong the time, we can increase the temperature or cook the starch under elevated
pressure. Rather than atmospheric pressure. So we can cook under the autoclave, or we
can put it in the retort. Or. How many or? We can use the starch which can start to gelatinize at a lower temperature.
Meaning we can use a starch with a lower onset of gelatinization. So this are the different
ways. We will come to that. So the conclusion from the experiment, the onset of gelatinization
shifted to a higher temperature when the water content is limited. So, we can see the effect
of this. I asked this question a few times in this
exam already. Because it is very important. You can see here, this is an example in excess
water, we can see that complete gelatinization is achieved. This picture below is a real
picture form a real experiment. This picture below shows that when we put dye, the green
color is actually protein. Because this is wheat flour. The green colour there is actually
protein. The blue color there is the amylose-iodine complex. So this is a system under limited
moisture and limited water. So some gelatinization still occurs, but it is still limited. You
can see some granule structure is still visible although they are deformed they are still
there. So this excess water system is an example of products like soup. This one is products
like cookies where we have very low amount of water. And in cookies also, we have sugar.
So when we add a lot of sugar, sugar itself is a very hydrophilic molecule and they are
small molecules. So it can compete with water more efficiently than the starch. So when
we add more sugar, it will bind to more water molecule. And there will be less water molecule
for starch to gelatinize. And that also gives the effect to a similar low moisture system.
When you add sugar or anything that can bind water more efficiently than starch. That will
also give the same effect like a low moisture system. So when we have more sugar, the effect
will increase the gelatinization temperature of the starch. So when we add more sugar and
we want to achieve complete gelatinization, we have to take a few steps to overcome that
problem. So that is the effect of ratio of water to starch on gelatinization. So let's
look at another effect which is the processing condition. We have to take a few steps to
overcome that problem. That is the effect of ratio to water to starch
on gelatinization. So in this case it is a processing condition. Shear. So why do we
have shear. Because we mix. We homogenize. There is always some form of shear during
processing. In this case we have normal and waxy maize. Remember the difference between
normal and waxy maize terms of amylose content Normal maize contains about 25% or less. Waxy
maize contains less than 1% amylose. When the maize starch gelatinizes, waxy maize granules
will swell much more faster than normal waste so the viscosity will increase very fast.
But then, it will reach the maximum swelling and become very fragile and it will also now
start to break and rapture and the viscosity will also drop very fast. So that is the characteristic
of waxy maize. Normal maize will lose its viscosity rather slowly. The same also her.
Waxy maize granules are more fragile compared to normal maize. Because normal maize has
25% amylose and that provides the strength to the granules. Compared to way maize which
contains only 1%. So we can see the effect here. So in normal maize, after shear and
waxy maize after shear. I think the picture tells again ten stories. A thousand stories.
I do not need to convince you. But the picture will convince you. The conclusion here is
why we see such significant difference here, because waxy maize granules are more fragile
and they are more prone to disruption, disintegration by shear. So now if you measure the viscosity
when they have reached the same gelatinization temperature. So we measure which in has a
higher viscosity. Assuming that we start at the same concentration. We will imagine that
this one has a higher viscosity. But mind you, later on when we talk about the application
and selection of starch, viscosity is not everything. So, actually in terms of mouth
feel, in terms of the rheological properties, in terms of the overall perception, in terms
of the stickiness and stringiness. They are all different. So viscosity is not the only
criteria for selection of starch. Later we will come to that . So that is the effect
of shear. Next is the presence and effects of other
ingredients. And in this case fat, lipid. In most food we always have fat. So when we
have fat, the fat for now will modify the gelatinization properties of starch. In what
way? How? The fat will form complex with the amylose and we know that amylose is a component which is responsible in the retorgradation
process. So when the fat forms complexes with the amylose, it will reduce the tendency of
the starch to retrograde, because now amylose is not available for crystallization. Because
it has formed complexes with fat. It has been sort of rendered inactive in a way. Because
it has form complex. Not available to crystallize. So what happens when we add fat? Again I would
like to illustrate the point with pictures. You case see here A, B, C, and D. we use SEM.
A, is the micrographs of a potato starch granule headed at 800C for 10mins. The interlaced
network is leached out of the amylose. The interlaced refers to the *** web structure
here. It is really a beautiful picture. Beautiful in a sense that they can capture this effect.
So you can see that the amylose leach out of the granules. All this while, we have been
imaging it. So actually when we capture it, It looks like that. How do we describe it?
It looks like a interlace network, a *** web structure. Or something likes a thread
or whatever. This granule swells, because it has been heated to 800C. For 800C for potato,
it might be slightly over or on the peak. Maximum swelling. Not yet ruptured. There
is a special technique, to freeze the process in time and to capture it. It is the more
advanced version. But thank God we have this. So we can show you. Now B, here, is potato
starch granules heated at 800C but now instead of 10 minutes we prolong it to 30 minutes.
Three times longer. So here more and more amylose leach out form and sorts of wrapped
up the granule. So we have more and more of an interlaced network which forms around the
granules. So this structure reminds me of an alien. Where it wraps around something
like this also. It also looks s like a *** web. So we have more and more amylose which
forms a network around the granule. C is potato granules, heated at 30 minutes but in the
presence of .25% C16. 1-monoglceride. It is a very efficient emulsifier. 1-monoglyceride.
So what happens here? This 1-monoglceride, There is an absence of leached amylose. It
is smooth. There is no interlaced or ***-web structure. So where has the amylose gone?
Where has the amylose gone? Inside or has it disappeared, dissolved? It has formed a
complex with the monoglyceride and it prevents it from leaching out to outside the granule.
And here, D. Potato starch granules heated at 800C for 30 minutes but in the presence
of 1% C18 type monoglyceride. Instead of 0.25%. So it is 1%. C18 type monoglyceride. The leached
amylose is higher than c. so form this experiment, this type of emulsifier compared to this kind
of emulsifier is less effective than this one. When we look at the amount of amylose
being leached out. To apply this knowledge, where we apply emulsifier to products like
noodles. It is done to reduce the stickiness of the noodles surface. So products like instant
noodles, we can use these emulsifiers. So when we add the hot water to these instant
noodles, you don't get a very stick structure. It looks very smooth and so on. So that is
the effect of lipid on the structure. But how does the formation of amylose-lipid complex
affect gelatinization? It does not say here. It just shows you. But how does it affect
the gelatinization? Would it increase or shift the gelatinization temperature to a higher
or lower temperature? Higher? Why? You
can see it is more difficult for amylose to leach out. But how does this affect the gelatinization?
You have to relate it with the capacity of the granule to swell. When the amylose forms
a complex with lipid, the indirect or direct effect of that, is to reduce the tendency
of the granules to swell. It slows it down. So, slow down swelling means, it will shift
the onset of gelatinization to a higher temperature. So that is the affect the fat emulsifier to
the gelatinization of starch. Yes. Phaik Hoon. You are not happy. If the amylose is present
in the surface, it will also form complex. And yes maybe, because during gelatinization,
we do not expect the emulsifier molecule. That is why you can see the difference between
this emulsifier C16 and C18.it depends on the efficiency of the emulsifier to form complexes
with the amylose. And, you can find it in the book. The ability of the emulsifier molecule
to form complexes with the amylose can be ranked. And we have the so call, amylose lipid
complexes index. So the more efficient it forms complexes, the less tendency for the
granules to swell. But, if it is not very efficient. Meaning that during gelatinization,
we would allow the granules to swell a little bit. That means there is a little bit of amylose
that has already been leached out on the surface. But later this amylose can also form complex
with the lipid. But in this case, the change of onset of gelatinization would not be shifted
very significantly. So the conclusion here. Let's say we carry out this experiment with
4 or 5 types of emulsifier. The higher the onset of gelatinization is shifted to higher
temperature, and the more efficient is the emulsifier in forming complex with the amylose.
It depends on the size of the molecules. Because the fat during cooking can also breakdown
to fatty acid, especially if the pH is quite low. So it is depending on the length of the
fatty acid chain. If we use emulsifier, remember that emulsifier can also have C8, C18, C16,
palmitic. It Also depends on the structure of the polar group. If you can still remember
the subject on emulsifiers. The polar group can be very small. The polar group can be
a big chain. The polar group can also have a branch. And the emulsifier chain can be
a C18 tail. It can have a branch, a double bond and etc. So it depends on the structure.
So different emulsifiers can have different efficient as we have seen in this picture.
Because we do not look at the concentration alone. This is C16 1-monoglyceride. But 0.25%.
This is 1% C18 type 1-monoglyceride.Again, this is how efficient in the emulsifying forming
complex with the amylose. The concentration is not necessarily perfect. Well we now have
to go back to IMK 209. When we learn about how emulsifiers can affect the emulsion stability.
In this case, the role of the emulsifier is the surface active property. To form a good
emulsion, the emulsifier must form a complete layer around each droplet of the oil. So it
is complete coverage. So in that case, the concentration will play a role. 0.25% and
1% will give a defense. In this case, it has nothing to do with the source active property
of the emulsifier. But is on the ability of the emulsifier to form complex with the amylose
component, And to form complex, remember if you can imagine now. The amylose will form
a helix structure and the lipid or the emulsifier molecule will go inside that coil. Do you
think it's easy to go inside the coil? So now the structure of the emulsifier will play
a role. How big is the polar group, how long is the tail. Whether it has branch or not.
So we can't really tell from the structure alone. So this is where we need to dome experiment
to see the efficiency of each type of emulsifiers. But of coz we do not need to do that, as there
is a lot of information available regarding this. The guideline we can use if we want
to choose the emulsifier in terms of bakery application for bread, cookies, cakes and
so on is by looking at the complexing index. And this information is available.
This picture tells us a thousand stories again. We have the control. In this case, it is high
amylose potato starch it is a hybrid type of potato. In nature, there is no high amylose
potato starch. But in genetic engineering, maybe this entire starch can be made into
high amylose. In Europe, they eat a lot of potato. That is why they do a lot of research
abutting potato. In Germany, there is a potato research institute, where they do a lot of
research on potato. In Thailand, we have a cassava research institute. In Malaysia, we
have the sago research institute, in Sarawak. So anyways this experiment compares the time
for high amylose starch. All of this are high amylose starch. But the variables here are
heating time. We have 600C. Control means without heating. There is an increase from
60 to 1000C, here. So we add iodine. I read the text down here. The effect of high amylose
starch on the texture of cooked potato. This is potato tuber, is cooked, and then we take
a slice it then add iodine and look it under the microscope. It is not powder. We cook
the powder. We cook the potato tuber. Then we take a slice, add iodine and look under
the microscope. And the effect of this on the texture of cooked potato. Section of tubers
from a control line and a high amylose starch line. The control line means o tony has 25%
amylose. Stained with iodine after boiling at 600C or 1000C. The starch of the control
line, gelatinizes and swells at temperature above 680C. So the starch in the cook samples
swell, to fill the cells completely. In contrast, the high amylose starch has a much higher
gelatinization temperature. And cooking does not swell the granules of the starch depreciably.
Giving the potatoes a succulent structure, with more free water. So the purpose of this
study is to compare the texture when you bite the tuber between normal potato starch and
high amylose starch. So when we heat to 600C, we can see the normal starch already has some
blue, iodine stain. And this one not so. And this one has swelled depreciably compared
to this one. It may be not that obvious. But when we increase it to 1000C, the normal starch,
the granules swell depreciably but this one still not so. So when we have this kind of
cell structure in the potato. So when we eat high amylose potato starch compare to normal
starch, the high amylose starch will give a more succulent structure. How do I describe
that? More succulent structure with more free water. How do I describe the succulent? Can
you imagine a succulent structure? I can. When you eat normal starch, when you cook
the potato. But this one, you can feel the structure more. There is more bite. It is
supposed to retain more free water. So when you eat the high amylose potato starch, there
will be more water released when you bite the starch. It is so difficult to explain
this. But only if can imagine that. If you cannot, you go back and sleep and try to imagine.
So we stop her. So I will see you all next week.
