Quantitative Determination of Polyphenolic Compounds in Medicinal Plants Under Varying Nitrogen Fertilization and Light Interception.

Polyphenolic compounds are precious non-nutritive chemical compounds having antioxidant and antimicrobial properties, directly involved in the mechanism of plant resistance against infectious diseases.  A rapid and sensitive spectrophotometric method for the quantitative determination of polyphenolic compounds (total phenolics and total flavonoids) in medicinal plants including Trachyspermum ammi, Foeniculum vulgare and Nigella sativa; were used in current study. Seeds were planted in the experimental fields under three types of light i.e., white light, green light and sun light. Varied nitrogen fertilization was done as second parameter in the sequence of 80, 90, 100, 110 and 120 Kg ha^-1, along with a control at same time (with light variation). Sample preparation procedure for polyphenolic assays included sonication, extraction in methanol (80:20), purification by centrifugation, subsequent series of reactions and determination by using spectrophotometer (flavonoids at 765nm and phenolics at 510nm). Standard curve was constructed by using quercetin as a standard for flavonoids and gallic acid for phenolics. The tested spectrophotometric method has been characterized with good linearity (R²=0.998) in the quercetin concentration range 0.2, 0.4, 0.6, 0.8 and 1.0 μg mL^-1, while in the gallic acid concentration range 0.05, 0.10, 0.15, 0.25, 0.50 μg mL^-1. This study concluded that there is no remarkable effect of light variation on the quantity of total phenolics and total flavonoids in medicinal plants while in case of nitrogen fertilization, quantity of polyphenolic compounds was inversely proportional to the increase in nitrogen concentration. The obtained results also demonstrated that the spectrophotometric method for the determination of polyphenolic compounds is less time-consuming, cheap, reproducible and suitable for routine laboratory analysis.