Phenolic Compounds in Food

Phenolic compounds are natural metabolites widely represented in plants which have recently gained special attention for their beneficial effects on human health. Polyphenols show antioxidant activity due to their ability to scavenge free radicals and to act as metal chelators. As a result of their antioxidant activity these compounds are able to protect tissues from oxidative stress thus preventing cell damage as in the case of neurodegenerative and cardiovascular diseases. The numerous phenolic compounds that mainly derive from secondary plant metabolism of the shikimate pathway can be subdivided into nonflavonoids, flavonoids, tannins and lignins, according to the variety of simple phenolic units. Moreover, basic structure can be substituted with various groups giving mainly glycosylated or acylated derivatives, or more complex molecules. Many scientific studies have been conducted in order to characterize phenolic compounds and to correlate their antioxidant activity with their medical benefits. Chemical characterization of phenolic compounds usually requires as a first step the extraction from food and later the use of more sophisticated techniques, mainly liquid chromatographic methods such as LC-MS, LC-MS/MS, LC-NMR. The main source of polyphenols is nutritional, since they are found in a wide array of edible products such as fruit (apples, blackberries, cherries, citrus, cranberries, grapes, pears, plums, raspberries, and strawberries), vegetables (broccoli, cabbage, celery, onion and parsley), honey, wine, chocolate, green tea, olive oil, and so forth. Polyphenols strongly affect the sensory properties of food such as color, taste (astringency and bitterness) and smell. The type of polyphenols contained in plant-derived foods and beverages depends on which raw material is used for their production. Their identification allows the tracing of the vegetable source and this can be extremely important in food characterization. However, the original phenolic pattern can be modified by the extraction process or following chemical and biochemical reactions. Anthocyanins, for instance, show only limited stability as they are affected by a number of factors such as pH, light, water activity, enzymes, oxygen, temperature, duration of processing and storage conditions