Evaluation of the phenolic content and antioxidant activity of sunflower seeds under deficit irrigation conditions

Abiotic stress like deficient irrigation might affect the synthesis of secondary metabolites in plants, which has several pharmacological effects. In this study, the effect of water deficit was determined on sunflower (Helianthus annuus L.) seed protein content, antioxidant activity, phenolic content and flavonoid and phenolic compounds of defatted seed extract for industrial usage. One sunflower genotype was planted in a field with six irrigation regimes (IR) under water deficit conditions that were set according to evaporation values measured during the 7-day irrigation interval (Kcp: 0, 0.25, 0.50, 0.75, 1.00 and 1.25) in a randomised complete block design. Results indicated that total phenolic content of seed extracts varied between 1.29-1.96 times higher than that under drought stress conditions (IR1). The antioxidant capacity of seed extracts was 7.82 (IR2) and 9.87% (IR4) higher than under drought stress conditions. The most abundant phenolic compounds that accumulated due to low water deficit (75%) were gallic acid and catechin. Based on principal component analysis, the biplot generated from PC1 and PC2 indicated that phenolic compounds in different irrigation regimes were collected under four subgroups. The drought stress conditions separated higher caffeic acid in a subgroup distant from the other irrigation regimes.