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. 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.)
Since most of the polyphenols in apples function as antioxidants, it’s not surprising to see so many health benefit studies focusing on the antioxidant benefits from apple. Particularly strong is the ability of apples to decrease oxidation of cell membrane fats. This benefit is especially important in our cardiovascular system since oxidation of fat (called lipid peroxidation) in the membranes of cells that line our blood vessels is a primary risk factor for clogging of the arteries (atherosclerosis) and other cardiovascular problems. Apples’ strong antioxidant benefits are also related to their ability to lower risk of asthma in numerous studies, and their ability to lower risk of lung cancer. In addition to their unusual polyphenol composition, an apple also provides us with about 8 milligrams of vitamin C. While that amount is not a lot, it’s still important, especially since the recycling of vitamin C in our body depends on the presence of flavonoids and apples do an amazing job of providing us with those flavonoids.
The cardiovascular benefits of apples are well-documented in research studies, and they are closely associated with two aspects of apple nutrients: their water-soluble fiber (pectin) content, and their unusual mix of polyphenols. Total cholesterol and LDL-cholesterol are both decreased through regular intake of apples. In some studies, “regular intake” has meant apple intake very close to the level of one whole fresh apple per day. As mentioned earlier, the strong antioxidant composition of apples provides us with protection from possible oxidation of fats (called lipid peroxidation), including fats found in the bloodstream (like triglycerides) or fats found in the membranes of cells linking our blood vessels. Decreased lipid peroxidation is a key factor in lowering risk of many chronic heart problems. Recent research has shown that the quercetin content of apples also provides our cardiovascular system with anti-inflammatory benefits. (Our blood levels of C-reactive protein, or CRP, are reduced following consumption of apples and researchers believe that the quercetin content of apples is the primary reason for this drop in CRP.) What a fantastic combination of cardiovascular benefits from such a widely available and delicious fruit!
Benefits for Blood Sugar Regulation
This area of research on apple benefits is relatively new, but it’s already awakening the interest of an increasing number of food scientists. At many different levels, the polyphenols in apples are clearly capable of influencing our digestion and absorption of carbohydrates, and the overall impact of these changes is to improve regulation of our blood sugar. The impact of apple polyphenols on our carbohydrate processing includes:
Slowing down of carbohydrate digestion. Quercetin and other flavonoids found in apples act to inhibit carbohydrate-digesting enzymes like alpha-amylase and alpha-glucosidase. When these enzymes are inhibited, carbohydrates are broken down less readily into simple sugars, and fewer loads are placed on our bloodstream to accommodate more sugar.