Download CSIRO_The Hungry Microbiome Project_Starch-SD

CSIRO_The Hungry Microbiome Project_Starch-SD
[Image shows a person’s hand writing on a whiteboard and text appears: The Hungry Microbiome. A diagram is drawn
beneath the title]
Narrator: This is Ormando(?). This video was created as part of the Hungry Microbiome Project, which I made at
CSIRO.
[Image changes to show a person’s hand writing on a whiteboard and text appears: Starch – major source of
carbohydrate in the human diet. A diagram is drawn beneath the text]
In this video we’ll explore the carbohydrate, starch. Starch is the major source of carbohydrate in the human diet.
We have it every day. Examples of starchy food include potatoes, bread, pasta and beans.
[Image changes to show a person’s hand drawing on the diagram and text appears: Potato, bread, pasta, beans]
Starch is stored in plants and seeds, and is used as an energy source. In this video we will look at where and how
starch is stored. Then we will learn about the structure of starch and how it is digested in the human body. Finally
we’ll focus on resistant starch. So let’s begin this journey by looking at a regular plant. Here we have a regular plant
with roots, and it’s receiving some sunlight so that the plant can participate in what’s called photosynthesis.
[Image changes to show a person’s hand drawing a diagram of a plant]
If we zoom into the leaf of this plant we can find plant cells.
[Image changes to show a person’s hand drawing on the diagram and text appears: Plant cell]
So here is a cell, with a cell wall.
[Image changes to show a person’s hand drawing on the diagram and text appears: Cell wall (contains cellulose)]
The cell wall of the plant cell is made up of the carbohydrate known as cellulose. Within the plant cell we can also find
the nucleus, the rough endoplasmic reticulum, the smooth endoplasmic reticulum, golgi apparatus, ribosomes,
vacuole.
[Image changes to show a person’s hand drawing on the diagram and text appears: Nucleus, rough endoplasmic
reticulum, smooth endoplasmic reticulum, golgi apparatus, ribosomes, vacuole]
And here is what’s known as a chloroplast, the organelle that carries out photosynthesis.
[Image changes to show a person’s hand drawing on the diagram and text appears: Chloroplast]
And actually within the chloroplast we can find starch granules, where starch is stored.
[Image changes to show a person’s hand drawing on the diagram and text appears: Starch granule (contains starch)]
So let’s have a closer look at the chloroplast. So here we are looking at one chloroplast.
[Image changes to show a person’s hand drawing on the diagram and text appears: Chloroplast (pigmented
organelle)]
A chloroplast is a pigmented organelle because it participates in photosynthesis, and therefore is pigmented and
contains colour.
[Image changes to show a person’s hand drawing on the diagram and text appears: 5mm]
Transcribed by: www.transcriberonline.com
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Chloroplasts are about five micrometres in diameter, but the size can vary again depending on the plant. Chloroplasts
contain thylakoids and all the structures related to photosynthesis, but within the chloroplast you can find starch
granules.
[Image changes to show a person’s hand drawing on the diagram and text appears: Starch granule]
The starch granules are where starch is located. However starch is not only stored within chloroplasts, it is also stored
within another organelle known as amyloplasts. So let’s have a look at where amyloplasts come from. A good
example is by looking at wheat.
[Image changes to show a person’s hand drawing a diagram of wheat]
Now wheat contains grains.
[Image changes to show a person’s hand drawing on the diagram and text appears: Grain, Seed]
If we look inside a wheat grain there is a region in it called an endosperm. Endosperm, the region endosperm are also
found within seeds.
[Image changes to show a person’s hand drawing on the diagram and text appears: Endosperm]
Anyways, endosperm is the region that contains starch granules, stored in amyloplasts.
[Image changes to show a person’s hand drawing on the diagram and text appears: Endosperm contain starch
granules stored in amyloplasts]
So essentially amyloplasts are found within endosperms. So if we were to look into this endosperm area of the grain
and the seed we can find amyloplasts.
[Image changes to show a person’s hand drawing on the diagram and text appears: Amyloplasts (non-pigmented
organelle)]
Amyloplasts are non-pigmented organelles. It is non-pigmented because it contains no colour. As you can see
amyloplasts are made up mostly of these starch granules.
[Image changes to show a person’s hand drawing a link on the diagram]
Now seeds contain many amyloplasts because they need all this stored energy as they grow, and therefore it’s no
surprise that roots of plants also contain many amyloplasts for energy reserves. So if we were to differentiate
chloroplasts to amyloplasts, it would be that chloroplasts contain transitory starch granules, and amyloplasts have
reserve starch granules.
[Image changes to show a person’s hand drawing on the diagram and text appears: Chloroplast – transitory starch
granules; Amyloplast – reserve starch granule]
Let us zoom at a cross section of a starch granule and focus more on it. The starch granule can vary in size, from one
micrometre to a hundred micrometres, depending on the plant.
[Image changes to show a person’s hand drawing on the diagram and text appears: 1-100 mm]
Starch granules contain granule rings.
[Image changes to show a person’s hand drawing on the diagram and text appears: Granule rings]
Now running through these granule rings we find glucose polymers.
Transcribed by: www.transcriberonline.com
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[14m:43s]
[Image changes to show a person’s hand drawing on the diagram and text appears: Starch is composed of two
glucose polymers]
Starch is made up of two specific glucose polymers. Let’s zoom into this section of the granule to learn a bit more
about them. Now the granule as I mentioned have granule rings. The granule actually have alternating crystalline and
amorphous regions.
[Image changes to show a person’s hand drawing on the diagram and text appears: Alternating crystalline and
amorphous lamellae]
Here are the alternating amorphous and crystalline regions.
[Image changes to show a person’s hand drawing on the diagram and text appears: Amorphous, Crystalline]
Now running through these regions we have the two glucose polymers. As you can see the crystalline region, they
have the defined branched glucose polymer running through them.
[Image changes to show a person’s hand indicating to the diagram drawing]
Within the amorphous region we can actually find an unbranched glucose polymer.
[Image changes to show a person’s hand drawing on the diagram and text appears: Starch is composed of two
glucose polymers: Amylopectin; Amylose]
The unbranched and branched glucose polymers are the two glucose polymers that make up starch. These two
glucose polymers are known as amylopectin and amylose. So the unbranched glucose polymer is amylose, and here
the branched glucose polymer is known as amylopectin.
[Image changes to show a person’s hand drawing on the diagram and text appears: Amylose; Amylopectin]
So amylose is a chain, linear chain of glucose molecules connected by alpha 1-4 glycosidic bonds.
[Image changes to show a person’s hand drawing on the diagram and text appears: Glucose; α 1-4 glycosidic bonds]
Amylopectin on the other hand are made up of many linear chains of glucose molecules, but with branch points. The
linear glucose are connected by alpha 1-4 bonds, and the branch points are connected by alpha 1-6 bonds.
[Image changes to show a person’s hand drawing on the diagram and text appears: α 1-4 bonds; α 1-6 bonds]
Interestingly amylopectin, the branched glucose polymer, make up 70 to 80% of the starch granule, so typically there
would be a great... there would be a greater amylopectin to amylose ratio.
[Image changes to show a person’s hand drawing on the diagram and text appears: Amylopectin make up 70-80% of
starch granules]
In reality the amylose and amylopectin are not flat; rather they form coils, like so. Here is an amylopectin in a coiled
form.
[Image changes to show a person’s hand drawing on the diagram and text appears: Amylose and amylopectin are
coiled structures]
Humans eat starch and the amylose and amylopectin coils can be digested by humans to glucose, which will then be
subsequently used for energy. Now that we know how starch is stored within the starch granules, let us see what
happens when we humans eat it.
[Image changes to show a person’s hand drawing on a whiteboard and text appears: Starch]
Transcribed by: www.transcriberonline.com
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So here we have bread, which contains starch, it contains amylose and amylopectin.
[Image changes to show a person’s hand drawing on a diagram and text appears: Amylose; Amylopectin]
And here we have a hungry human and his digestive system.
[Image changes to show a person’s hand drawing a diagram of a man and the digestive system]
The amylose and amylopectin, the starch, is digested and absorbed predominately by the small intestine.
[Image changes to show a person’s hand drawing on the diagram and text appears: Starch is digested and absorbed in
the small intestine]
So within the small intestine here the starch will encounter digestive enzymes which will break it down into glucose
molecules.
[Image changes to show a person’s hand drawing on the diagram and text appears: Digestive Enzymes; Glucose]
However in reality starch is digested at different rates. A portion of starch can be digested quickly, another portion
slowly, and another one can resist digestion in the small intestine altogether. So for example, here we have starch
represented as amylopectin.
[Image changes to show a person’s hand drawing on the diagram and text appears: Starch]
Starch can be divided into three types, depending on the rate it is digested in the human body.
[Image changes to show a person’s hand drawing on the diagram and text appears: Rates of digestion]
Starch can be rapidly digested, which is the portion of starch digested within 20 minutes of ingestion.
[Image changes to show a person’s hand drawing on the diagram and text appears: Rapidly digestible starch – portion
digested within 20 min]
Starch can be slowly digested, which is the portion digested between 20 minutes to 120 minutes.
[Image changes to show a person’s hand drawing on the diagram and text appears: Slowly digestible starch – portion
digested between 20-120 minutes]
And finally a portion of starch can be resistant to digestion altogether, with the remaining portion after 120 minutes.
[Image changes to show a person’s hand drawing on the diagram and text appears: Resistant Starch – portion not
digested. Remaining portion after 120 min]
Let us now focus on resistant starch. A better way to define resistant starch is the fraction of starch that is not
digested in the small intestine but reach the colon is called resistant starch.
[Image changes to show a person’s hand drawing on the diagram and text appears: Fraction of starch that is not
digested in the small intestine but reach the colon is called resistant starch]
Examples of foods that are high in resistant starch include unripe bananas, cooked and cooled potatoes, beans and
legumes.
[Image changes to show a person’s hand drawing on the diagram and text appears: Unripe bananas, cooked and
cooled potato, beans, legumes]
The extent to which starch resist digestion can influence the development or progression of certain diseases, such as
diabetes and colon cancer. This quality of resistant starch have many health benefits for the human body. One of the
Transcribed by: www.transcriberonline.com
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main reasons why this is so is because resistant starch undergo fermentation by bacteria in the colon to produce
substances such as short chain fatty-acids.
[Image changes to show a person’s hand drawing on the diagram and text appears: Resistant starch is fermented by
bacteria in the colon]
Therefore it is important that we see and understand how resistant starch actually resist digestion in the human body.
There are actually four types of resistant starches.
[Image changes to show a person’s hand drawing on the diagram and text appears: 4 Types of resistant starch]
The types are the physically inaccessible starch, resistant granules, retrograded starch and chemically modified starch.
[Image changes to show a person’s hand indicating to the diagram and text appears: Physically inaccessible starch
(RS1); resistant granules (RS2); retrograded starch (RS3); chemically modified starch (RS4)]
Now let’s look at each one and see how they differ. Remember that each one is a type of resistant starch, and that a
resistant starch is starch which has resisted digestion in the small intestine. So type one resistant starch is the
physically inaccessible starch, because it is physically inaccessible. A good example of this is because of the presence
of the cell wall that protects the starch granules.
[Image changes to show a person’s hand drawing on the diagram and text appears: Physically Inaccessible Starch
(RS1) – presence of cell wall protects starch granules]
So here is a plant cell with its tough cell wall. Here are the starch granules within the plasts.
[Image changes to show a person’s hand drawing on the diagram and text appears: Starch granules; cell wall;
digestive enzymes]
And so with the cell wall the digestive enzymes secreted by the humans cannot access the starch. Foods that are high
in type one resistant starch are legumes and partially milled grains.
[Image changes to show a person’s hand drawing on the diagram and text appears: Examples: Legumes and partially
milled grains]
Resistant starch type two, called resistant granules, is resistant to digestion because of the characteristic of the starch
granules itself.
[Image changes to show a person’s hand drawing on the diagram and text appears: Resistant Granule (RS2)]
Each plant contains starch granules with amylose and amylopectin. The starch granules differ in size, shape, amylose
and amylopectin ratio, amongst other things.
[Image changes to show a person’s hand drawing on the diagram and text appears: Amylose and amylopectin]
It is thought that a combination of these factors make some granules have a more compact structure, and so are more
resistant to attack by digestive enzymes.
[Image changes to show a person’s hand drawing on the diagram and text appears: Compact structure of the starch
granule protects the starch. Digestive enzymes]
Good examples of food containing resistant starch type two are raw potatoes and unripe bananas.
[Image changes to show a person’s hand drawing on the diagram and text appears: Examples: Raw potato and
unripe banana]
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[14m:43s]
Resistant starch type three, also known as retrograded starch, is the most abundant of the resistant starches. This is
what we eat most of the time, such as bread and cereals.
[Image changes to show a person’s hand drawing on the diagram and text appears: Retrograded starch (RS3)]
Now resistant starch type three is formed through food processing, it is formed by first cooking the starch and then
cooling it down. So let me draw it out and explain. Resistant starch type three is formed when the starchy granules
containing amylose and amylopectin are cooked in water, they are hydrolysed.
[Image changes to show a person’s hand drawing on the diagram and text appears: Amylose and amylopectin;
cooking, “hydrolysis”]
This causes the starch granules to become completely hydrated and gelatinised.
[Image changes to show a person’s hand drawing on the diagram and text appears: Granules swell. Amylose leaks
out. Gelatinisation]
The starch granules will swell up and the amylose will start to leak out. The starch is in a gelatinised form.
[Image changes to show a person’s hand drawing on the diagram and text appears: Cooling]
Then when the food is cooled down the amylose and amylopectin will recrystallise to a completely new compact
structure. This process is known as retrogradation or recrystallisation.
[Image changes to show a person’s hand drawing on the diagram and text appears: Retrogradation (recrystallisation)]
And here we see a rearrangement of amylose and amylopectin to a more crystalline structure.
[Image changes to show a person’s hand drawing on the diagram and text appears: Rearrangement of amylose and
amylopectin to a more crystallise structure]
We also see amylose cross-linking occurring through hydrogen bonds.
[Image changes to show a person’s hand drawing on the diagram and text appears: Amylose cross-linking of hydrogen
bonds]
This new structure formed by cooking and cooling decreases access to digestive enzymes, and so this type of starch
will resist digestion. Examples of food containing resistant starch type three are cooked and cooled potatoes.
[Image changes to show a person’s hand drawing on the diagram and text appears: Examples: Cooked and cooled
potatoes]
Now finally some authors have proposed a type four resistant starch, which is the chemically modified starch.
[Image changes to show a person’s hand drawing on the diagram and text appears: Chemically modified starch (RS4)]
This type of starch is said to be possibly attributed to the different bonds formed through chemical modification, and
so with these new bonds this type of starch will resist digestion by digestive enzymes.
[Image changes to show a person’s hand drawing on the diagram and text appears: Starch (amylose and
amylopectin). Chemically modified. New Bonds? Digestive enzymes]
Examples of food with chemically modified starches are certain cakes and breads.
[Image changes to show a person’s hand drawing on the diagram and text appears: Examples: Certain cakes and
bread]
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[Image changes to show all the diagrams drawn]
And so that concludes the video on starch and resistant starch. I hope you enjoyed it. Thank you for watching.
[Music plays and CSIRO logo appears with text: Big ideas start here www.csiro.au]
Transcribed by: www.transcriberonline.com
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