Flavonoids are a group of polyphenolic compounds present in many plants, fruits, vegetables, nuts, flowers etc. They exhibit a wide range of bioactivity and have gained much attraction last two decades because of its potential applications in biology, medicine, and chemical analysis due to their antioxidant, medicinal (antiviral, antibacterial, antiallergic effects) and complexion properties. One of the main properties of flavonoids especially quercetin is their oxidation by oxygen dissolved in water or organic solvents mainly in basic media.