Pulse crops are nutritious, but their seed coats are typically discarded, despite their high content of polyphenols. Polyphenol diversity among seed coats of five pulse crops was examined using a 30‐min liquid chromatography‐mass spectrometry (LC‐MS) method. Notable differences within polyphenol classes were observed among crops and genotypes. Polyphenol profiling is the first step in understanding how pulse crop seed coats can be better utilised and also in ultimately determining which polyphenols and biochemical pathways are important for human health benefits.

Pulse crop seed coats are a sustainable source of antioxidant polyphenols, but are typically treated as low-value products, partly because some polyphenols reduce iron bioavailability in humans. This study correlates antioxidant/iron chelation capabilities of diverse seed coat types from five major pulse crops (common bean, lentil, pea, chickpea and faba bean) with polyphenol composition using mass spectrometry. Untargeted metabolomics was used to identify key differences and a hierarchical analysis revealed that common beans had the most diverse polyphenol profiles among these pulse crops. The highest antioxidant capacities were found in seed coats of black bean and all tannin lentils, followed by maple pea, however, tannin lentils showed much lower iron chelation among these seed coats. Thus, tannin lentils are more desirable sources as natural antioxidants in food applications, whereas black bean and maple pea are more suitable sources for industrial applications. Regardless of pulse crop, proanthocyanidins were primary contributors to antioxidant capacity, and to a lesser extent, anthocyanins and flavan-3-ols, whereas glycosylated flavonols contributed minimally. Higher iron chelation was primarily attributed to proanthocyanidin composition, and also myricetin 3-O-glucoside in black bean. Seed coats having proanthocyanidins that are primarily prodelphinidins show higher iron chelation compared with those containing procyanidins and/or propelargonidins.

P olyphenols are a large group of secondary metabolites composed of various subclasses: simple phenols, phenolic acids, stilbenes, and flavonoids such as flavanones, flavones, dihydroflavonols, flavonols, flavan-3-ols, anthocyanidins, and proanthocyanidins (Vermeris and Nicholson, 2006; Piluzza et al., 2019). Polyphenols are involved in protection against various human diseases including cancers and cardiovascular diseases (Graf et al., 2005; Spilioti et al., 2014). The beneficial effects of dietary plant polyphenols have been attributed to their antioxidant properties (Antolovich et al., 2002; Manach et al., 2004; Pandey and Rizvi, 2009). Antioxidants protect cells from the damaging effect of reactive oxygen species by scavenging free radicals and singlet oxygen. Polyphenols are the most abundant antioxidants in the human diet and are present in fruits, vegetables, cereals, and legumes (Manach et al., 2004; Scalbert et al., 2005). Isoflavones are present almost exclusively in leguminous plants, whereas gallocatechin, epigallocatechin, and epigallocatechin gallate are present in legumes, grapes, and tea (Arts et al., 2000a, 2000b; Manach et al., 2004). Polyphenols play an important role in plant defense response to various fungal pathogens (Lattanzio et al., 2006). Several studies established the role of polyphenols in disease resistance against various pathogens, such as Colletotrichum circinans (Walker

Faba bean is a cool season grain legume that produces seeds with a high protein content. Seed coat tannins limit its use in food and feed. A low-tannin phenotype is controlled by either of two unlinked recessive genes zt1 and zt2. Liquid chromatography–mass spectrometry was used to characterize phenolic profiles of seed coat and flower tissue of three faba bean genotypes: CDC Snowdrop (zt1 gene), Disco/2 (zt2 gene), and ILB 938/2 (tannin-containing). For both tissues, clear differences in phenolic profiles of ILB 938/2 were observed in comparison to both low-tannin lines. Although seed coat phenolic profiles of zt1 and zt2 genotypes were similar, distinct differences were evident in flower tissue, suggesting that the gene action results in some different end products of the phenolic biosynthetic pathway. These distinctive compounds could be used as biochemical markers to distinguish between low-tannin phenotypes.

No abstract