Why fruit tastes sweet or sour based on chemical composition

Fruit

Why are some fruits sour, and other fruits sweet?

The answer to that question lies in the fact that the taste of any fruit is dependent upon the compounds present in that fruit. Fruits contain cellulose, proteins, starch, vitamins, certain acids, and fructose (or sugar), and when a fruit has more fructose than acid it tends to taste sweet (www.GeminiGeek.com). On the other hand, when a fruit has more acids in it than fructose, it tends to be tart, or sour. An orange for example has nearly equal amounts of fructose and acids, so it can have both a sweet and slightly sour taste, depending on how ripe it is, on the variety and on the climate it was grown in.

In fact when some fruits are raw, the Gemini Geek Website explains, they have more acids in them, but when they become ripe the "quantity of acids…decreases and the amount of sugar / fructose increases." An example of that process is the mango, a fruit that is sour and tart prior to ripening; however, once ripe, they are very sweet.

Also, when raw, a banana has a lot of starch, but when the skin of the banana turns from green to yellow that means that inside the starch has been "converted into fructose." it's a chemical change inside the fruit that turns the starch into fructose. What about two apples, both the same variety but one is quite sweet and the other is a bit on the tart side? The explanation is that there are variations in the quality of soil, the climate (warm or cold, wet or dry), the amount of water given to the fruit tree and the way in which they are pruned, etc. When it comes to a lemon, the acid will always be in greater amounts than fructose, hence lemons will always be sour (Gemini Geek).

How do humans interfere in this process by consuming grains and fruits?

Assuming this question refers to the consumption of a fruit, such as a concord grape, by a human, certainly there will not be seed dispersal when the seeds work through the digestive system and into a facility that breaks down raw sewage for sanitary purposes.

Does the seed use the fructose or starch in fruits for its metabolism?

In the immature green tomato seed, a fruit, after a period of "transient starch accumulation" that is accomplished by "developmental changes in the key enzymes in the sucrose" (sugar). As the fruit develops, the "suc synthase, fructokinase…and soluble and insoluble starch synthases" tend to decline dramatically in concert with the decrease in the starch levels. In other words, in the tomato seed, both the sucrose and starch play important roles in metabolism (Schaffer, et al., 1997, p. 739).