Polyphenols in plants are protectors, beautifiers and communicators. With diverse structures and functions these phytochemical compounds fortify plant health and resilience, and attract the best pollinators.
About Polyphenols
Polyphenols give blueberries their deep blue color, wine its complex flavor and roses their alluring scent. They're tools of survival, reproduction, and defense in competitive environments.
Polyphenols are characterized by multiple phenol units, aromatic rings with hydroxyl groups.. They create countless plant-based molecules.
They can be categorized into several groups. These include flavonoids, phenolic acids, tannins and ellagitannins. Polyphenols appear in dark chocolate, and red wine.
Polyphenols are defense mechanisms for plants against UV rays, disease and pests. In grapevines, flavonoids like anthocyanins give grapes their characteristic color and protect them from oxidative and fungal damage.
During stressful conditions, plants often speed up polyphenol production.
They also influence growth and development within plants. Polyphenols help regulate cell processes, resulting in healthier plants.
Types of Polyphenols
1. Phenolic Acids
The simplest forms of polyphenols, phenolic acids are precursors to more complex structures. Phenolic acids include caffeic, ferulic and gallic acid. In fruit, vegetables, and grains they fortify structure and antioxidant defense.
Ferulic acid is particularly effective at absorbing UV radiation, protecting plants from sun damage. It's found many plants including rice, wheat, oats, pineapple, grains, beans, coffee beans, artichokes, peanuts and nuts.
2. Flavonoids
Flavonoids create the vibrant color found in fruits, vegetables, and flowers. They're further divided into subclasses such as anthocyanins (red, purple, and blue pigments), flavones and flavonols.
Beyond their aesthetic benefits, flavonoids are potent antioxidants. They protect plants from oxidative stress caused by pollutants, UV radiation, and pathogens.
Bees can see ultraviolet light. Many flowers have flavonoid patterns invisible to the human eye, guiding pollinators to land at the nectar source.
3. Tannic Acid
Tannic acid, also known as tannins, is a complex polyphenol found in bark, leaves, and fruits. These compounds bind to proteins, giving them an astringent taste.
Historically, tannins are instrumental to the tanning of leather. They react with the proteins in animal skin and make it more durable and resistant to decay.
The characteristic dryness when drinking red wine is due to the tannins in grape skins and seeds. Tannins excel at plant defense against herbivores. Their astringent unpleasant taste deters most, but not all, consumers.
4. Ellagitannin
Ellagitannins are another class of tannins, often found in fruits like pomegranates and raspberries. They are known for their unique structure and action against oxidants in plants.
They include castalagin and its variations in oak and chestnut. They're famous for adding flavors and color to wines and spirits stored in oak barrels.
The ellagitannins in pomegranates, including punicalagin isomers, exist in the sarcotestas or fleshy seedcoats; peel (rind); bark or heartwood of Punica granatum. They help shield against UV and other cell damage.
Facts About Polyphenols
Polyphenols enhance soil health by promoting diversity and activity within microbial communities. Compounds released into the soil foster beneficial interactions with microbes, which improve nutrient availability for plants.
Polyphenols can enhance decomposition of organic matter within the soil. This natural process helps maintain soil structure, prevent erosion, and encourage water retention.
Polyphenols also affect the food chain, influencing herbivores and the organisms who prey on them. For instance acorns have high tannin levels, which deter some mammals but don't affect squirrels.
Acorns are the favorite food of wild squirrels. These busy rodents bury them as a food stash and often start new oak trees. Dietary preference shapes the foraging habits of animals and the ecosystem reliant on them.
Quercetin found in such food as apples, grapefruit, okra and onions is an antioxidant, targeting free radicals in plants. Amygdalin in flaxseed and apple seeds prevents consumers from chewing them, so the seeds pass unharmed through the digestive system.
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