Drought stress influenced sesamin and sesamolin content and polyphenolic components in sesame (Sesamum indicum L.) populations with contrasting seed coat colors

•Drought increased sesame antioxidant activity especially in the tolerant genotypes.•Gallic, ferulic and caffeic acids, apigenin and rutin were the major component in sesame.•Four seed colors were identified in separate groups based on the studied traits.•Dark color seeds had more amount of caffeic, ferulic and ellagic acids, TPC and RSA.•Light color seeds had more sesamin, sesamolin, p-coumaric and gallic acids and oil. Ten sesame genotypes planted under two irrigation regimes of 60% and 90%, as the maximum allowable depletion (MAD), were used to investigate the effects of drought stress on certain quantitative and qualitative characters of sesame seeds with four contrasting coat colors. The polyphenolic components, sesamin, sesamolin, total flavonoid content (TFC), total phenolic content (TPC), radical scavenging activity (RSA), seed yield, and oil content of the seeds were also examined. Results revealed that drought decreased seed yield, oil content, sesamin, and quercetin but increased TFC, TPC, and RSA as well as most of polyphenolic components and sesamolin. The drought-tolerant genotypes including Markazi1 exhibited higher chlorogenic, ellagic, and p-coumaric acids as well as TFC, RSA, and rutin. While the dark-seeded sesame genotypes contained higher caffeic, ferulic, ellagic acids as well as TPC and RSA, the light-seeded ones were richer in sesamin and sesamolin as well as p-coumaric and gallic acids. The findings of the study provided basic information on the changes in some seed secondary metabolites when sesame was subjected to drought stress. The results also confirmed not only the presence of considerable amounts of antioxidants in sesame seeds but also differences in secondary metabolite levels among the sesame seeds with different seed coat colors.