Water-soluble phenolic compounds and their putative antioxidant activities in the seed coats from different lentil (Lens culinaris) genotypes

The seed coat is a major byproduct of lentil processing with potential as a sustainable source of antioxidant polyphenols. Profiles of water-soluble phenolic compounds and antioxidant activities of seven genotypes of lentil which includes both normal-tannin and low-tannin seed coats were investigated. Antioxidant activities were assessed using four antioxidant assays, and phenolic compounds were quantified using liquid chromatography mass spectrometry (LC-MS). Total phenolic content (TPC) varied significantly among genotypes and ranged between 1519 ± 140 and 6502 ± 154 μg/g. Thirty phenolic compounds were identified with kaempferol tetraglycoside, catechin-3-glucoside and procyanidins being the dominant compounds in normal-tannin seed coats. Kaempferol tetraglycoside predominated (80-90%) in low-tannin seed coats. Antioxidant activities strongly correlated with TPC (r > 0.93) with a 6-9 times higher activity in normal-tannin than that of low-tannin lentils. Without flavan-3-ols and procyanidins, low-tannin seed coat may not exert strong antioxidant potential, whereas normal-tannin seed coat contains water-extractable natural phenolic compounds with promising antioxidant potential.