Apple's Amazing Polyphenols. In the past five years, no area of apple research has been more dynamic than the area of apple polyphenols.
The balance of these phytonutrients in apples is far more unique than many researchers previously suspected.
In terms of flavonols, quercetin is the primary phytonutrient found in apples, and it's far more concentrated in the skin than in the pulp.
Kaempferol and myricetin are also important apple flavonols. Chlorogenic acid is apple's primary phenolic acid, and it's found throughout the pulp and also in the skin.
If apples are red, it's because of their anthocyanins, which are largely restricted to the skin. When an apple is more uniformly red in color, or when its red color is deeper in hue, it's because there are more anthocyanins.
In terms of catechin polyphenols, epicatechin is the primary nutrient found in apples. The flavonoid phloridzin accounts for 98% of the flavonoids found in the apple seeds.
The total polyphenol contents of apples range from about 1-7 grams/kilogram of fresh pulp, but this ratio gets much higher in the skin, underscoring the special value of apple skins for deriving optimal polyphenol benefits from this fruit.
In fact, in animal studies, there is a very commonly used standardized apple extract called standardized apple peel polyphenol extract, or APPE.
You might wonder why apples end up with such an amazing array of polyphenols. In this context, it's fascinating to see that recent research studies show polyphenols to be the favorite mechanism used by apples to protect themselves from UV-B radiation.
Cells in the skin of apple that conduct photosynthesis are especially sensitive to UV-B light from the sun.
Many of the polyphenols in the skin of apples can actually absorb UV-B light, and thereby prevent UV-B from damaging the photosynthetic cells in the apple skin. Polyphenols, then, are like the apple's natural sunscreen.
It is also interesting to note that the amazing polyphenol content of apples is related to their easy browning when sliced open or bruised.
Inside the cells of apple skin and pulp are enzymes called polyphenol oxidases, or PPOs. When the cells of the apple are sliced through or physically damaged when an apple is dropped, the PPOs start oxidizing the polyphenols in apples, and the result you see is a browning of the damaged apple portion.
It's important to handle apples delicately in order to protect their health-supportive polyphenols! (Also in this context, it's worth mentioning that damaged apples not only turn brown from the oxidation of their polyphenols, but they also start releasing relatively large amounts of ethylene gas that can pose a risk to other undamaged apples.
This phenomenon is why people say that "one bad apple can spoil the whole bunch." Once again, the problem of ethylene gas from apple bruising or other damage underscores the importance of handling this amazing fruit with tender loving care and removing any damaged apples from groups of apples stored in bulk.) Source is here.