So now we have a rainbow, I want you to play around with, to decorate your dish. All the colors, but then there are some color we may not want to see. Browning. You may recognize that when you're eating vegetables. when your vegetable turns old they become yellowish and gradually they become brown. And sometimes for some of the fruits or vegetables that when you cut them open, when you leave them there for awhile, they turn brown. So this is a process we call browning. So what happens is that when all this vegetable or fruits they were like being bitten on, or you have cut them, at the edge where you cut them usually you see this browning, very obvious. What's going on in fact that is referring to a situation that, that is damaged. And when the damage occurs this browning enzyme is going to come in. I'll tell you what the enzyme is. It will come in and it will convert some of the components in these plant cells into a product which is dark in color. And they are brownish, and so therefore they aggregate, and you see them deposited in the cell. And so as a result, you can see this particular apple on one end. Actually you have a freshly cut apple white in color, but you leave them there for long enough. They turn brown. Now so what is going on? In fact what happened, browning is referred to, a condition we call oxidation of compounds related to phenol. And these phenols. Or we call them hydroxybenzenes. And what happen is that when the oxygen comes in they are going to modify these two growths and as a result this product would eventually generate this dark pigment. Very similar to what we have as melanin, dark in color. So, what do we do is that when we see plants for example in banana a lot of time we leave them there for a while over a time in a few days or so they greatly turn very dark. And not just vegetables. Sometimes even for animal. You remember when you buy some shrimps from the market, when you leave them there for long enough, you find that they start to develop all this darkened area in the head. That's also because of this phenolic component, which is being converted into dark pigments. Now, so how can we prevent them? It's relatively easy. We need to understand what's going on. The browning enzyme involved in fact is an enzyme called polyphenoloxidase. This polyphenoloxidase, its function is to add the oxygen group onto this phenol compound. And because they need to add oxygen to the compound, that means oxygen needs to be provided, so we have an enzyme and we have oxygen. Add onto the phenol, the phenol becomes dark, so it is very easy to think about how to eliminate this possibility, either you don't allow enzyme to work or you don't allow oxygen to be available. So if you can do that, limiting the supply of oxygen or inhibiting the enzyme, you will be able to prevent browning. So how can we do that? Very easy. We notice that enzyme, these are proteins. Enzyme can be very easily denatured by your increase, by increasing the temperature. So we can trick this plant by heating them. Think about that. You, have you ever cooked soup with apples? And after the cooking you find that apple never turned brown. Because the enzyme has been destroyed. Okay. So, of course, you're not going to cook the apple at this point. What you do is that you can subject it to blanching. Blanching means that you simply dip the apple. And to very hot water for a very brief moment, before it get cooked. Basically it kills the enzyme. Now so with that, of course with the cooking sometimes it also help to generate some of the flavor of this plan or vegetable. And at the same time it softened a little bit the texture. So it's changing multiple thing. If you don't want to use the boiling water you can do some other thing. For example, we say enzymatic reaction. How can we inhibit this enzyme from functioning? Very easy. Because we notice enzyme. In fact you need to recognize this oxygen and you need to recognize the substrate so that they would go through the reaction. But then, sodium chloride, this is a very commonly found component in the kitchen. It turns out that it bind onto this enzyme in something which is called non-competitive way, meaning that, once it bind with the enzyme, it doesn't want to go away. So, if it's not going away, basically the enzyme is totally inactivated. Even though you have plenty of oxygen around. You have plenty of this phenolic compound around. They are not going to become brittle. So, were if that so, you may recognize a lot of people. After they prepared. Or cut open the apple. They like to dip into some water, but of course, you need to remember that when you dip it into salt water, you are having some salty taste. So this salty taste, make sure it's not strong, otherwise, it would generate taste and taste into action. And, of course, there's other way that you can do. for example, we say that this reaction, in fact, it need to take place and, it depends on actually what kind of pH that it would alter acidity, is going to affect the rate of this reaction. So we noticed that when you put it in a very acidic condition, such as you try in a malic acid, tartaric acid or citric acid, when the pH, whenever it's below 5 in fact there's been polyphenoloxidase, it is not going to be very active. So once you put in acid. They are not going to have any reaction going on. So they're not going to be darkened. Now, very easily you can think about that. You want to be acidic. You also want to gather, get rid of the oxygen. What would be the better way? Vitamin C. You all know that vitamin c is a antioxidant. It prevents oxygen from oxidizing it's product. And at the same time it provided acidic condition. So, next time, if you have the convenience and you have the vitamin C at home, the best way to preserve a browning apple is to dip them into vitamin C. And it may actually provide you additional protection for your health. Now and of course one area that we can focus on is that well, eliminate oxygen. So that's what the people do. a lot of people they would like to cut the fruit and before they get brown, dip them into syrup. And in the syrup you can protect them from in direct contact with the oxygen in the atmosphere and, of course, a better way to do that is you put them into the can and take a vacuum and remove all the oxygens, although you need to recognize that whether you can really 100% eliminate all the oxygens. If you leave them there for long enough, they can still go with the browning process. So, with all these mashes, essentially, we do have a color, we mean not one to see in the vegetable, browning, but there are plenty of way for you to take care of it so that they remain very colorful.
