Phenolic compounds in plants are numerous and belong to secondary metabolites of the plant organism. From a chemical point of view, it is a group of compounds having a phenolic or hydroxyl group on the aromatic ring. There are various ways of synthesis of phenolic compounds. The most important two pathways of biosynthesis are the shikimic acid pathway and the malic acid pathway. Plants produce a wide range of secondary metabolites that cover a variety of functions, such as defending a plant against herbivorous organisms, mechanically supporting the plant, attracting pollinators and fruit spreaders, or inhibiting the growth of other plants. The most commonly represented group of phenolic compounds are flavonoids. Flavonoids are synthesized via phenylpropanoids pathway and serve as UV protectors and in pathogen defense, for plant and microorganism communication and for the regulation of reactive oxygen species. There is great interest in the world for phytochemicals as bioactive food components. Consumption of fruits and vegetables in human diet can prevent some diseases due to their high antioxidant activity. Free radicals play an important role in the processes of food deterioration, the degradation of chemical materials and also contribute to more than one hundred disorders in humans. In recent years, there has been an increased interest in the use of antioxidants for medical purposes, and a great deal of attention has been paid to cereals and legumes because of their strong antioxidant properties. There are many methods of detecting phenolic compounds and calculating total antioxidant activity. They are roughly divided into two groups: in vitro methods and in vivo methods. Some of the in vitro methods are DPPH, TEAC, FRAP, SOD, ORAC and many others, and in vivo methods are GSH, GSHPx, CAT, GGT, etc.