Phenolics are another class of secondary metabolites that offer many benefits to the plant and have additional applications to human health and wellness. Included in phenolics are lignin, flavonoids, and tannins.


Tannins, which are non-volatile compounds produced in leaves, bark, woods, seed, nuts, and unripe fruit, can be poisonous and are often used by plants to avert predatory herbivores. A great deal of research has been conducted surrounding the mechanism of their protective benefits allowing researchers to confirm one of the many ways tannins function. Once ingested, tannins interfere with the metabolism of plant proteins, making them difficult for animals and insects to digest and absorb. Other tannins have beneficial properties and have been shown to control environmental threats. These beneficial tannins have gained popularity in the nutritional world being most commonly associated with tea and red wine; however, tannins are found in a large number of other plants including ginger, vanilla, and cinnamon.

Lignin is a structural compound useful for giving wood its strength; in fact, without lignin, trees could not grow tall. It is the cement that holds wood cells together. This special compound works by reinforcing the cell walls of certain plants to make them especially durable and strong. Lignin protects the structural integrity of plants by preventing their destruction by hungry insects or herbivores (except for those that have adapted to lignin, such as termites). In addition to its structural properties, lignin has many cleansing properties.

Flavonoids are a class of compounds that can exist in a wide range of types such as flavones, chalcones, anthocyanins etc. They are known to possess a wide variety of biological activities. Commonly found in fruits and vegetables, anthocyannin flavonoids are revered for their brilliantly hued pigments and are responsible for giving the red, orange, and pink colors to many flowers and fruits. Their bright colors assist in attracting beneficial pollinating insects. Additionally, flavonoids have a unique chemical structure that makes them excellent antioxidants. In plants, this structure allows absorption of UV light from the sun to protect the plant’s genetic information from damage. They may even play a role in plant growth. Not only do flavonoids benefit the plants themselves, but have been shown to confer many similar health benefits to humans. For example, the flavonoids extracted from the orange and tangerine peels have antioxidant properties that help maintain cholesterol already in the healthy range. The flavonoids found in onion and garlic are thought to contain antioxidant properties and support the immune system.

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