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Effects of substituents on the acidity of phenols: Existence of electron attracting group, (for example-NO2, -X, - NR, -CN, -CHO, -COOH) on the benzene ring increases the acidity of phenol since it enables the ring to draw much more electrons from the phenoxy oxygen and so releasing easily the proton.
Coffee is particularly rich in bound phenolic acids, such as caffeic acid, ferulic acid, and p-coumaric acid. Phenolic acids found in blueberries include gallic acid, p-hydroxybenzoic acid, coffeic acid, p-coumaric acid and vanillic acid. Flavonoids -- Flavonoids are a subclass of polyphenols.hey can be classified into the following categories: Polyphenols occur in all plant foods and contribute to the beneficial health effects of vegetables and fruit. Their contribution to the antioxidant capacity of the human diet is much larger than that of vitamins.