Well, knowing that now we have the saliva at work, we want to taste something. And we know that how many different tastes are there. So in fact, there are infinite possibilities for us to combine all these tastes together. So let's go through some of this. First of all, let's look at how can we taste something? We need to understand that there's something called a threshold. We say that all this tastes, they need to activate the receptors so that we can perceive the sense. What happen is that you need to reach a certain level of concentration before you can sense it and that different tastes, they have a different level of threshold. For example, in this case, we say that saltiness - you can try sodium chloride, the table salt. In fact, we would be able to tell the difference between 0.01 molar, a very low concentration. Anything below that, in fact, we can hardly tell of the - this and the taste of the saltiness. For sourness, we are more sensitive. We can like a sense up to the level of like almost one in 1,000-fold of a molar solution, we can still sense that it is sour. So the same applies for the other. Bitterness; we are very sensitive. Umami; we are very sensitive. But look at saltiness and sweetness; actually, we need to have a high concentration in order to perceive the sense. Now having that, we will say that threshold level is the level at which a taste can be noted and it is determined by a few things and it varies from individual to individual. What are the factors? It depends on the number of papillae we have in our tongue and it is depending on the number of taste bud in each of the papillae; it depends on the number of sensory cells and the number of receptors per cell. So you multiply all of them together. It would tell you that well, how many receptors are there so that you would be able to sense a certain taste molecule. Now, knowing that the taste act through this specific receptor, we would say that is there any way that we can block it? For example, I don't like bitterness; can I find something to block it? Yes, we can. In fact, in the industry, they do have something called the taste blocker inhibitor. What do they do? In fact, these are the molecule which is resembling the taste molecule very much. They will bind onto the receptor; but then they bind on the receptor, they don't fire. So what happens is that essentially you have a large number of receptors available on the tongue. They sense, they can bind to the taste molecule. But then, because most of them now they are occupied by this taste blocker and they don't fire. So when you are eating additional substance which is having the same taste, you simply don't sense it anymore. So in this, it allows us to use it as like a craving stopper. We can also use it to remove some of the bad taste, such as sometimes we don't want to have bitterness. So we add the bitterness taste blocker so that we eliminate this part of the taste. On the other hand, we also need to know the - even at the sub-threshold - that means at a level below the threshold - in fact, even though we can't sense the taste, they are still doing something. And at this point, they got concentration. What they do is that they can influence the taste of other taste molecules. So how was that observed? Here is some of the very common type of so-called sub-threshold level effect. Think about that. If you have some food which you increase the level of salt at a sub-threshold level, what you find is that if the food originally is tasting sweet, it would become sweeter. If originally is sour, it becomes less sour. It's because of at the sub-threshold level, the taste of salt, in fact, can somehow influence the perception of the other tastes. The same thing happened for acid. When you add acid, in fact, it would increase the sense of saltiness. The same thing the sugar; we use it all the time. Sugar can reduce the saltiness as well as reduce the bitterness. Now I'm trying to go give you some example of that. We say that well, in fact, the modification takes place because the acid somehow modified the saltiness essentially is a event of how the pH is affecting the function of the ion channel. Remember, acid is hydrogen ion. Hydrogen ion is talking about the pH. And we know that the sense of saltiness is based on this ion channel and we know that ion channel function at a different pH with different efficiency. So if you change the pH because you're eating something acidic, even though it is at a level which is below your detection; but it's already taking effect by modulating how the ion channel for the perception of the mineral. So therefore, it can alter its response. So the same thing is that for organic acid concentration, it can also enhance a salt response in a very similar way. Now, only when the salt concentration is greater than the threshold, then you'll start sense that saltiness, solely relying on its concentration dependence response. Now, having that, let's look at some of the application. We say that while salt can mask the bitterness, we know that it takes place because we can do an experiment. You can take sugar, which it tastes sweet; you can take urea, which it tastes bitter; and you take salt and combine them all together. And you'll find that in this combination, in fact, you'll find that it's sweeter - less bitter - because salt enhance sweetness and salt also suppress bitterness. And with this particular mixture, compared with another situation that you don't have the addition of any salt. Why is that? In fact, we have such a hypothesis and, in fact, it works pretty well, is that the salt offsets the weakening of the sweetness sensation caused by the bitterness of the urea. So because of that, now we can have food which have all this three kind of sensation in combination. And it will generate a perception which is more appealing than simply tasting each of them alone. Now, in fact, this kind of interaction, there's no simple rule among them. I'm showing you this particular graph simply to highlight that how variable they are. Depending on whether at the low concentration, medium concentration or high concentration, in fact, all these four different taste; the sweetness, saltiness, sourness and bitterness - they have different kind of interaction. Sometimes they suppress each other, sometimes they enhance each other, sometimes they may have no effects depending on what the concentration is. So the key is that when you next time prepare a meal, when you have all these tastes all together need to be put into a particular dish, make sure that you tune them at the right level so that they would have the right interaction and suppression and enhancement that you want. Now, I didn't talk about the fifth taste, which is umami. The very funny thing is that umami, we say that it is a taste of amino acid and nucleotide. And interestingly, it has a synergistic effect and it modify all the other flavor, meaning that it's improving the sweetness, the saltiness, the bitterness, as well as the sourness. Why is that? Because basically, umami binding - or the taste of the umami allows the other receptor to have a better binding with the corresponding molecule. So how's it like in application? We say that a lot of times when we cook dishes, we like to add a few thing. We like to add tomato. Tomato is very rich in amino acids. We like to add cheese. Sometimes we put soy sauce. Soy sauce is from the soybean, which is also rich in amino acid. Or we put meat stock, that you simply cook the soup out of meat. And whenever you add these, the dishes - usually they taste better. Now remember, when you add all these things into the food, it enhance it only at the level when it's low. But if you are using too much of it, we say that at the supra-threshold MSG - MSG is the same as umami - if you use too much of it, in fact, they dominate the entire sensation. And what it turns out is that it will suppress the effect of whatever other taste. So remember now, we have all the interaction between the sourness, saltiness, sweetness and bitterness. We also have the umami that come in; at low concentration it enhance everyone, but at high concentration, it suppress everyone. So make sure that when you're using them, you would use them appropriately. Now at the end, we talk about it. Well, there is some suppression when you put things together. What exactly is mixture suppression? We say that when two tastes are put together, both of them give you a lower sensation of that particular taste. What exactly is that? For example, we say that when you put salt together with bitterness, two together, in fact, salt always suppress the bitterness. And so that's how why, when we are eating something such as pretzels, we drink beer. Beer, in fact, tastes bitter. But when you have pretzel, the pretzel has some salt on it. The saltiness of it, in fact, help to take away that bitterness of beer. Now, that's why the two would come together very well. We also say that well, sugar can also suppress bitterness too. That's exactly why all the kids, we want to feed them medicine which is tasting very bitter; but then we add syrup together with it, so that they taste sweet. Now - so in beverages, sweetness is suppressed by citric acid at supra-threshold level. So what it means is that when you add a lot of acid, even though the - whatever drink - they have a lot of sugar in it, still you sense the sourness more that the sweetness. Now so that's how this different taste can be really put into application when you're preparing any specific dish. And in experimental setting, I want to show you here is that while sugar sweetness can suppress the bitterness. So we ask people to do experiment to show that actually how the perception of the sweetness and the bitterness is. If you ask them to sense the sugar, how much is the intensity; very high. When you ask them to taste something bitter, the quinine; very high. But if you ask them to taste both of them together, you'll find that the sweetness come down; also the bitterness. Both of them come down. Now the funny thing is the following; well, we can use this so-called "the suppression and then the release" method. What we do is that we can ask the individual to take the quinine first; take something very bitter and then give them a mixture of sweetness and bitterness. Look at what happened. Over time, when you ask them to taste the quinine, the bitterness, that particular sense becomes suppressed and in such a mixture, in fact, the sweetness would be enhanced. In such a case, what it tells is that it tells you that by putting food in a certain sequence, it allows you to enhance some taste and suppress some taste. The same thing happen after you try sucrose and then taste a mixture. The sense of sweetness goes down and the sense of bitterness goes up. So again, importantly, the sequence of the food in a particular menu is important because it allows you to enhance some taste at a particular time and it allows you to suppress some taste at a particular time. Now, so what I want to do is that in the following, we're going to show you one demonstration. We hope to show you that using different kind of concentration of the sweetness, we would be able to generate suppression of bitterness and that would illustrate this particular principle very well.