Contrasting effect of salty taste on watermelon

It is said that when you eat a watermelon with salt on it, it tastes sweet.

In this way, when different tastants stimulate the taste cells at the same time, one taste is enhanced by the other tastant, which is called the taste contrast effect.
There are two types of this contrast effect: [simultaneous contrast] and [continuous contrast].

Simultaneous contrast: Taste the flavors at the same time
Example: watermelon with salt, oshiruko with salt

Continuing Contrast: Continue to enjoy the taste
Example: Licking a candy and then eating a mandarin orange
• Sweetness is enhanced by adding a small amount of salt.
Examples: Oshiruko, salted manju, watermelon with salt
For 10% sugar solution, when adding 0.15% salt (100g sugar, 1.5g salt)
For 25% sugar solution, when adding 0.15% salt (250 g sugar, 1.5 g salt)
For 50% sugar solution, when adding 0.05% salt (500g sugar, 0.5g salt)
When no salt is added in 60% sugar solution
tastes the sweetest

It is also said to be enhanced by a slight bitterness. (Quinine 0.001% liquid)

● Saltiness (1-2%), bitterness and sweetness are enhanced by a small amount of acetic acid (0.01%).
Example: sake and acid

●Sourness and umami are enhanced by a small amount of salt.

Contrast effect over time
(1) Saltiness or sourness is felt more strongly immediately after tasting sweets.
(2) Sweetness is sweeter immediately after tasting bitter food.
From here on it's subjective.

It seems that there are few people who think about the relative effect of taste when cooking. However, in fact, everyone uses it in home cooking, just without being conscious of it. You can find it if you put a little awareness, such as adding vinegar to cold noodles or adding soy sauce to sweet sauce.