7.7: Demonstration – What is the best way to prevent browning?

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From the course by The Hong Kong University of Science and Technology

The Science of Gastronomy

206 ratings

The Hong Kong University of Science and Technology

The Science of Gastronomy

206 ratings

This course introduces a number of basic scientific principles underpinning the methodology of cooking, food preparation and the enjoyment of food. All topics covered have a strong basis in biology, chemistry, and physics application. Among others, they include the consumption of cooked food, the physiological and evolutionary implication of the senses, geographic and cultural influences on food, and the rationale behind food preparation. We will also discuss issues such as coupling of senses to improve sense stimulation; altering flavor by chemical means; and modification of the coloration to improve the appearance of dishes. Following the video demonstrations of the scientific principles of cooking, you will learn to recognize the key ingredients and their combinations for preparing good healthy food. At the end of this course, you will be able to: - appreciate the scientific basis of various recipes; - develop your own recipes by integrating some of the scientific principles into new dishes; - recognize the influence of the material world on human perception from the different senses; - appreciate the art of integrating science into cooking and dining. Important Note: This course is not designed for people with special dietary needs such as vegetarian, diabetic, and gluten-free diets. If you feel uncomfortable with any part of the assignments or activities of this course, you can substitute some of the ingredients or ask friends and family members to help with the tasting of your assignments. Alternatively, you may skip that specific assignment provided that you have fulfilled all other qualifying requirement to pass the course. Course Overview video: https://youtu.be/H5vlaR0_X2I

From the lesson

Module 7 and Module 8

This week, we will look at how fruits and vegetables can enhance the quality in cooking and to learn about the properties of meat.

7.0: Fruits and Vegetables - Topic Outline0:29

7.1: What gives the rigid texture to plants?9:59

7.2: How can we manipulate the texture of plants?12:44

7.3: What gives green color to plants?12:28

7.4: Why some plants are not green in color?7:03

7.5: Demonstration – Manipulating the color of red cabbage3:37

7.6: Why does the apple turn brown?7:34

7.7: Demonstration – What is the best way to prevent browning?5:55

7.8: What are the prominent tastes in fruits and vegetables?8:32

Assignment 8 – Instruction Video2:51

Assignment 8 – Result Sharing4:23

7.9: Fruits and Vegetables - Topic Summary1:27

Meet the Instructors

King L. Chow
Professor
Division of Life Science
Lam Lung Yeung
Associate Professor
Department of Chemistry

You remembered we are talking about the browning reaction.

This browning reaction involves enzyme and oxygens.

So we want to demonstrate to you how we can stop this process from taking place.

So may I have my assistant, Zoe. Okay, so in this experiment we are going

to do the following. You may see that in front of us in fact

we have laid a four glasses of water, they are just tap water.

So we need to get them prepared into different conditions.

So let's do it one at a time. So, the first one we are going to use,

lemon juice. So with us, in fact, we already have some

lemon juice prepared. We are going to put about five ml of

lemon juice into the first glass. Okay.

Alright, so that's lemon juice. Remember lemon juice is both acidic and

also it has vitamin C. Now the next one we want to compare is we

want to put some vinegar in it, into the second glass.

Again, more acid that equal amount. So the vinegar is going to provide just a

acidic condition but that's not vitamin C.

So therefore it is not going to be anti-oxidants available.

Alright and the third glass we're going to put some salt in it, these are the

table salt we have, okay, that's good enough.

All right. We stir it a little bit.

Make sure that they are all dissolved. All right, we can just leave the spoon

here. Now, and for the fourth glass is, we do

not need to put anything in there. So it's just the control, without adding

anything. So what we're going to do is that we're

going to initiate a burning reaction. The burning reaction we start with an

apple. So we take this particular apple.

So we're going to cut it and then to slice it into pieces.

All right. And once they are cut open.

The apple is going to form slices and they would have surfaces which would be

exposed to the air. And in the air there will be oxygen.

So, in a way, we have the oxygen and we have the apple where there this enzyme,

the polyphenol oxidase is available. And together with all this phenyl group,

they are going to form compound, which is going to be brown in color and they're

going to be deposited. So what we going to do is that we'll put

one piece into each glass. And the final piece, don't do anything,

we'll simply leave it here, and allow it to be exposed to the air.

Now we'll see what happens. So we have this one, just the water.

We have the apple submerged in it. And this one we have the salt.

And this one we have the vinegar. And this one we have the lemon juice.

So, we will leave it here And we'll wait for some time.

And we'll come back and monitor how they look like.

And certainly we do expect that this particular slice when it's exposed to

air. Over time this browning reaction is going

to take place very actively and they're going to turn darkish brown.

And let's see what happened with the others.

So quickly, we've gone through 20 minutes.

So, let's see what happened. So this is the apple slice that we have.

Look at how it has turned, it is brown. So let's do a comparison.

Let's put the cutting board on this side, alright.

Now, so this one is the one which we simply leave it in the air.

this brown color. So now let's take the one which is

submerged in water, the second piece is in water how about the third piece, third

one is in sodium chloride solution okay so this is the difference and the next

one is the one submerge in vinegar solution.

And finally, we have the one we just submerge in lemon juice.

Okay, so let's take a look at it. You'll find that this is the one which is

simply exposed to the air. So you notice that all this brownish

color. This one is in just water, so it's been a

little bit isolated from the air submerged in water.

How about this one? Well, this one basically you don't see

much browning, this is the one in the sodium chloride.

So remember that sodium chloride in fact can be an inhibitor of that enzyme.

Now this one, it is in vinegar. So, acidic pH also inhibits that

particular enzyme. And this one is in lemon juice.

It is submerged in water, not in contact of oxygen and it has the ascorbic acid

which is anti oxidant and is also acidic. So therefore, certainly you notice that

when you put in all this inhibitor compared with the one just to the air or

this one seems to be a little bit isolated from oxygen, the air.

All those in fact they are having less browning effect

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