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