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This topic is also available on the online lecture but maybe partly. So upon request,
I will cover this topic. So basically what happens during frying, deep fat frying? Because
as we know one of the big application of fats and oil is for frying. Especially for fast
food. We use deep frying. I am sure also all of you have experience yourself, when you
fry food with oil. Some have bad experience. Some have good experience. Usually what we
observe when we fry food using the oil. The oil is very hot. We have to increase the temperature
well above 100 or 2000C So it is very, very hot. Then you put in the food. Whatever you
want to fry. Can be chicken. Can be anything. But always, or almost all of the time, the
food will contain water, moisture. It can be very wet. So the water content is very
high. When the wet food containing water, come in contact with hot water, so that is
when you see that reaction. Like a boiling reaction. So basically the water containing
the food just splashed off. Because the temperature is well above 1000C. So the water in the food
will vaporize, splash off and will actually try to escape from inside the oil into the
atmosphere. So that is why you see the vigorous boiling reaction. And sometimes you get something
also like, splash off from the food. It can get to your hand and even to your face if
you are not careful. I remember when my daughter, learn how to fry food. She is not the type
who likes to go into the kitchen and cook. Some of you maybe also. So when she learns
to fry the fish. So maybe some of you have also experience that. So have you ever imagine
the kind of reaction, the physical and chemical. The physical and chemical reaction that occur
in the food. Yeah. In the food as well as in the oil during frying. Many type of reaction
here. So we can actually talk about the hydrolysis
of the fat and the triglycerides. And then talk about the oxidation of fat and other
components in the food. Oxidation of the fat in the food as well as oxidation of the fat
in the oil itself, to produce various types of oxidized products. It can be good. It can
be bad. Good because it will oxidize the oil itself. The fat. Good because some of the
oxidation product itself can actually add to the characteristic flavor of the food.
So there is a good and bad side of the oxidation. So we can get oxidation. We can get hydrolysis.
And other kind of reaction that in the end will produce a compound. Some of this will
go into the food itself and control the flavor. And some of this will go into the oil. So
imagine now, the yellow color is the oil. And above that is the atmosphere. So now we
are looking into the changes of deep fat frying. I think it is good also to cover this in the
lecture. Because this is very, very important part of the application of fat or oil in Malaysia
as well. Who knows that you might go for an interview with KFC, McDonalds or any of the
industries that involve in this kind of business, where they do a lot of deep fat frying. And
they might ask you something about like this. And at least you have an idea.
Food. So imagine the food always contain water and other things. So it will come in contact
with the hot oil. Imagine this oil is very hot. Very, very hot. Okay. So, where to start?
Let us look at what happens to the water in the food. It will just vaporize in a split
second. It is so fast. So fast. So the moment the food comes in contact with the oil, we
just see that vigorous boiling reaction. Which actually the water actually forms steam, And
where the steam goes, it has to go out somewhere. It wants to go out to the atmosphere. So the
steam will from that boiling reaction which is the bubble and it will vaporize, goes off.
So we get the steam from the water. But remember, the food also contains protein and carbohydrates
and fats. And some other volatile flavor they have. And so this are volatiles. And these
volatiles will also escape together with the steam. So we have vaporization. Then the fat
itself, when come in contact with water, under very high temperature, it will hydrolyze.
So we have the hydrolysis of triglycerides now. The oil of coz. When the fat hydrolyzes,
it will produce the FFA, free fatty acid. If the triglyceride is partially hydrolyze
it will produce and from a mixture of diglycerides. Even maybe monoglycerides. And even glycerol
itself, glycerin. So it can be a mixture of this. As a result of the hydrolysis of the
triglycerides, under the influence of water and high temperature of the cooking oil. At
the same time, the vigorous boiling reaction, during the escaping of steam to the atmosphere
will draw in or pull in air from the atmosphere. So in air, of coz it contains oxygen. And
even in the food and in the oil itself, it contains dissolved oxygen. And now it pulls
in the air, the oxygen from air into the oil. And it will come in contact with the triglycerides.
The unsaturated bond with the triglycerides. It will be oxidized. So we have oxidation
there. We have oxidation, of coz. You have learned probably what happens during oxidation.
So it will go thru the primary oxidation. And then the secondary oxidation. And then
it will produce a range of peroxides and hydro peroxides. This is the primary products of
the oxidation. And will produce some other products from this thru fission. To produce
aldehydes, acids and hydrocarbons. So this are the compounds that can be produce as a
result of oxidation. And the presence of this compound at high temperature can promote other
type of chemical reactions. Can start another type of chemical reaction. Which is polymerization
of this to form a bigger compound? So another reaction that can occur during frying in oil
is actually polymerization. This polymerization from the small compound that from the oxidation.
So under the influence of high temperature it can produce bigger compound. So what we
have here is actually polymerization reaction. As we continue or if the frying is prolong,
more and more oxidation. More and more of this product will be form. And more and more
of this polymerize compound will be form. Polymeric compound by nature has a high molecular
weight. And it will actually contribute to the viscosity. It will increase the viscosity
of the oil. It will increase the viscosity of the oil. So, one of the physical changes
that can occur. Oxidation is chemical changes. This is a steam, vaporize and go out into
the atmosphere. That is physical changes. Polymerization that is chemical changes. The
effect of polymerization is the increase in viscosity. That is physical changes. That
is why earlier I said, during deep fat frying we have chemical and physical changes. So
as a result of the formation of the polymeric compound it will increase the viscosity of
the oil. It will measure the viscosity. The viscosity we increase. The effect of increasing
the viscosity during frying would be also to affect how easy the steam that is formed
to escape to the atmosphere. Imagine that we have fresh oil and compared to the oil
that we have used for frying from maybe 5 times. So the viscosity of fresh oil and 5
times. Oil you have used 5 times. Let us say this is B, the viscosity so higher. So the
steam that is form here will have a more difficult time to escape to the atmosphere. Beaus the
viscosity is higher. So if you have observed how the boiling of the fresh oil compared
to the oil that has been used for a few times. You will see that the oil which has been used
for a few times will have a more violent kind of boiling. You can also hear the sound. It
is also noisier. Imitate that. But it will increase the viscosity of the oil. Another
effect of increasing the viscosity of the oil, together with the increase in free fatty
acid in the oil due to the hydrolysis, It will cause the oil to form smoke. More smoke.
So when you fry using fresh oil, you hardly can see any smoke. But if you use the oil
a few times, you can see more smoke form. So the effect of. When more fatty acid is
form. This fatty acid will actually be. Some will go out of the oil. And some will remain.
And some will form actually other compounds. And the overall effect of this is actually
this is actually to reduce the smoke point. To reduce the smoke point of the oil. Smoke
point is the temperature when the oil start to form smoke. You learn probably in IMG 203
or IMG 204. Should be in IMG 203. Or maybe in Food Chemistry. I do not know. You learn
about the properties. So in smoke point. So some of the analysis that we do on fat and
oil is the smoke point. That is to show the stability of the oil and the quality of the
oil. Poor quality. Actually if you buy those oil in the packet sold in the packet or sold
in the big can. those are probably the lower grade. The lower grade oil. And in terms of
refining, In terms of the fatty acid content, it is maybe higher. Those oil have a smoke
point compared to the premium oil we buy in the supermarket. Meaning that it can from
smoke easily. Maybe high quality oil if you use 3 or 4 times, it is still ok. You do not
see smoke form easily. But the low grade. Not to say low quality. The low grade oil,
after you use maybe twice, you can see smoke form easier and more. So that is due to the
formation of the free fatty acid and also the polymeric compound that is form in the
oil during cooking. And remember all this compounds that is form, are actually will
accumulate in the oil. Will accumulate in the oil. If you do not remove them and you
use the oil over and over again, more and more will accumulate in the oil. Let us say
you buy any fried food from the shops in the street, especially 'goreng pisang'. I was
just going to give the example on that. Some of them use the oil many, many, many times.
Maybe they just filter the crust, crumbs and residues. They just remove the solid residue
but not the soluble residue in the oil. So when you fry the banana using that oil sometimes
it does not taste good at all. Like those McDonalds, KFC and so on, they also recycle
the oil. Do you think that they use fresh oil every time? Who have gone for industrial
training in KFC or McDonald? So we ask Alifa and Shafizan. So maybe you can share your
experience. How do they recycle their oil? They mix. But they do not do any kind of treatment?
You do not see it. They do. What this treatment does is actually to remove the soluble. Those
compounds that accumulate in the oil. Those small compounds, they remove them. Not only
the insoluble residue but also the soluble compound in the oil. Actually properly done,
if the process is properly done, the oil is quite. In terms of quality, almost like, almost
like near fresh. But they mix with the fresh oil. So that is how they maximize. Because
oil is expensive. So that is how they maximize. What is one of the major concerns now days,
if you follow what is the latest in food technology? It is the issue on acrylamide. Have you heard?
Acrylamide. Have you heard it on the newspaper? If you follow what is happening in the world
of food technology, if you are a good food technologist. If not then, you are still good.
So you should know that this is the latest issue on food safety. There is a group scientist,
if I am not mistaken from Sweden, they discovered not so recently, maybe a few years ago. Ok
still recent. A few years ago. They discovered that food containing carbohydrates and also
fat when heated at high temperature, they can produce this so called acrylamide. And
do you know what acrylamide? Acrylamide is a monomer that can form a bigger polymer called
polyacrylamide. Polyacrylamide is synthetic gel. We use in electrophoresis. We use in
many nonfood application. It forms gel. Very nice clear gel. I remember in my final year
research, I used polyacrylamide to prepare the electrophoresis gel. Polyacrylamide is
not dangerous at all. But of coz you do not eat. But basically it is safe to hold and
to touch. But before it forms gel, in the monomer form, acrylamide it is carcinogenic.
I remember when I read in the label, don't inhale. Make sure you do not get. The acrylamide
does not get into contact with the skin because it is carcinogen. Carcinogenic. So the scientist
discovered that during frying and even during baking, toasting, roasting, acrylamide can
form. So it actually caused an alarm. A big issue around the world. FDA, Food Drug and
Administration USA investigated this. So luckily they found. Actually they confirm that acrylamide
actually formed from various reactions. Somehow it is a complex reaction and it is not really
understood yet how the acrylamide formed during frying, high temperature baking, roasting.
They believe the Mallard reaction is also responsible. From the Mallard reaction thru
some other complex pathway and mechanism can form acrylamide. It has been confirmed that
acrylamide can be formed. But the good news is the normal level acrylamide formed during
frying and other high temperature process is not dangerous for the body. For our body
system. And it can be probably removed from the various ways. But there is a very small
amount. I think there is still research now around the world. And at what level the acrylamide.
And how much food you eat. The fried food until you reach that level where the acrylamide
accumulate above a certain level in your body and it can cause harm. It can cause cancer
and so on. So the lesson from this. So the message from this, maybe if you want to eat
fried food, or anything roasted toasted, baked, we eat in moderation. Like Shen she just eats
veggie. You do not fry. You fry also. Yeah. Occasionally. Otherwise you boil. But you
can still eat fried food, but eat in moderation. Moderate. That is the rule of thumb. Eat in
moderation. Everything is in moderation. So that what happens during frying?
If we follow the chemical reaction. As you can see here. This dash line shows the peroxides
and the amount of oxygen in the oil. And the oxygen absorb. You can see the oxygen absorb
is increase. Always increase. And you can see this is the various type of chemical reaction
which happens during deep fat frying. At the same time the viscosity as a function of frying
increase quiet dramatically. So the combination of the physical as well as the physical changes
bring about some desirable and undesirable effect on the food that has been fried. This
is what Shen asked me to explain. I do not know if I can explain. So you have this slide
right? The changes happen during frying. So wejust review that. Rate of oxidation increase
with temperature and oxygen. And presence of light and contact with pro oxidants. Especially
if we have copper. So if you fry in stainless steel fryer or container, then you do not
get this metal as a pro-oxidant. But imagine if you fry in the copper pot ,you get to leach
out into the oil and increase the oxidation. Polymerization forms a larger molecule and
viscosity increase. This is what I have explained. To decompose to form the volatile. Nonvolatile
decomposition products. So meaning during the frying just now will form a range of compounds,
some are volatile. So this will escape from the oil. Some are nonvolatile and this will
remain in the oil. So this can be removed by filtration maybe. And by using other ways.
The VDP are constantly being removed by the evolving steam. And the NVDP removed from
the frying oil via absorption by the food being fried/ by deposition on frying kettle
part/filtration. So as we use the oil more and more, the oil get darken because the protein
from the food and what not that we use, so we get the browning reaction. So it causes
an increase in darkening. So to reduce oxidation, most oil in the market
now, they add antioxidant. Synthetic antioxidant. BHA and BHT. It is very, very strong, powerful,
effective antioxidant. Okay. The more you use the oil. The easier the oil to smoke and
also to form foam, whey. So again in the industry, they add anti foaming to reduce the foaming.
So, replacement with fresh oil or mix with fresh oil if you want to recycle the oil.
Okay now. This is an interesting graph to show the FFA development during deep frying.
Remember free fatty acid form due to the hydrolysis of the triglycerides in contact with water
and high temperature. So we can plot free fatty acid on the x axis here. And say during
the prolong time is a function of frying time. And we are frying potato. Fresh potato. To
produce maybe potato chips, potato fingers, potato wedges. So we have three situations
here. High potato rate, low potato rate and zero rates. So what it means here is actually
refers to the amount of loading. The amount of potato that is being fried here.
So, we can say at high potato rate, we can get more free fatty acid to form as a function
of time. But low potato rate we have less. And at zero rates means just the oil without
the potato. But still, we still get the free fatty acid to form and increase as a function
of time. Only that is lower than the low potato rate and much lower than the high potato rate.
So here in the presence of potato, of coz we can understand that the potato contains
water. More potato contain more water will be release and come into contact with the
oil and form free fatty acid. Less potato, less water, less free fatty acid. Zero rate,
no potato. Why? We still have free fatty acid? Why we still have free fatty acid formed?
Oxidation. We are measuring fatty acid here. We are plotting fatty acid here. Well, we
cannot avoid the oil still get hydrolyzed because of one high temperature. Any oil,
at high temperature it will get hydrolyzes. In the oil, in the cooking oil, do you think
that there is no water? There is still some water. During frying, the oil is exposed to
the atmospheric. In Malaysia especially the RH is high and you still get some moisture
in the atmosphere that can come in contact with the oil and also cause some hydrolysis.
Especially at high temperature. So you still get some FFA, but the production
of FFA will be accelerated in the presence of food especially food containing high amount
of water. So. What we measure here, is free fatty acid.
Now, the same thing but we measure the formation of foam. This is what Shen is puzzled because
she could not explain. In this case, foam height compared to this one. High potato rate,
low potato rate, zero rate, it is to be expected. That is to be expected. But when we measure
the foam height, it is the other way around. Low potato is zero rates here. And high potato
is like this. Who can explain this? Those who have get the notes from their senior.
Maybe the senior has written down something. But it is okay. But if you can explain in
your own words based on your own understanding. Who want to try? Potato absorb the polymer.
So therefore what happens to the foam height? Absorb the polymer and therefore reduce the
viscosity and absorb some of the free fatty acid. Possible. Possible. We do not know what
really happen inside the oil right? So anything is possible. So Shen said that because the
potato absorbed some of the polymeric compounds that has been form and maybe some of the free
fatty acids, therefore reduce the formation of foam. It could be partly true maybe. I
am waiting for someone to try to explain. Phaik Hoon. This time I want an answer not
a question. I have explained. I have explained in the video. But Shen said no. So how did
I explain? I think that is correct but can you say again louder so that everyone can
hear. So that it can be captured by the camera. This one will go onto the internet one day.
So all of you are actually, it will happen sometime next year, once we have edited the
video. Because we are not going to put the 50 minute lecture on the internet. Probably
we want to make it into half an hour or less. So Phaik Hoon, your chance now? Ah Yin. Yin.
Exactly. Here. During the hydrolysis of fat in the oil, FFA can form and they can also
form digylecerides and monoglycerides. Depending on the extent of hydrolysis of the triglycerides.
And we know very well the triglycerides and the monoglycerides. At a certain amount, concentration,
we learn this in IMKL 209; can serve as an antifoaming agent. So the foam that is formed
can be sort of broken down by the diglycerides and the monoglycerides that is formed in the
system. It is a dynamic process, during frying. So it can actually reduce the foam at a certain
concentration. If you do
not do the job, the foam will increase again. So in general, that is what we will get especially
if the amount of water in the food is high. Because we will get more hydrolysis of the
triglycerides to form some diglycerides, monoglycerides and some free fatty acids. So, this is what
we will get. So this is how we explain this trend. At a low potato rate and a zero rate,
less hydrolysis of the fat. Less monoglyceride. Less foam in the first place. Less foam will
be formed. But if the foam formed, less mono and diglycerides is formed and therefore it
will not reduce the foam that much. So we get a higher foam height and a low potato
rate and zero rate. So if you say it is available and I have explained this in the video and if
you want to revise what we have covered here, please go back and listen to the video. I think that is about all. I am
glad that I managed to explain this. Actually I did not plan to explain about this part.
But I think it
is important. And please
also read more on
this topic. What else? So we stop here. The test will be
on Monday. Monday.