Biochemical Profiling of Phenolic Compounds in Lentil Seeds

Abstract

Lentil (Lens culinaris Medikus) is an annual cool-season legume with a variety of seed coat colours. Seed coat colour is an important grading factor that affects the market value of lentils. In lentil, two independent loci gray ground colour (Ggc) and tan ground colour (Tgc) determine the four basic seed coat background colours; brown (Ggc Tgc), gray (Ggc tgc), tan (ggc Tgc) and green (ggc tgc). The zero tannin locus (tan) is epistatic to the tgc locus, producing clear seed coats. Lentil is a good source of protein, carbohydrates, dietary fiber components, minerals, vitamins, and secondary metabolites that include phenolic compounds. Phenolic compounds produce different pigments in plants and bring health benefits to humans. The overall objective of this study was to determine the relationship between seed coat colour and phenolic compounds in lentil. In the first study, comparison of the phenolic profiles of four seed coat background colours in lentil (i.e., brown, gray, tan, and green) was performed using an optimized liquid chromatography-mass spectrometry (LC-MS) method. The results showed that for the levels of various phenolic compounds in lentil seeds varied with the seed coat colour. Specifically, seed coats of lentil genotypes carrying the homozygous recessive tgc allele (green and gray seed coats) had higher amounts of flavan-3-ols, proanthocyanidins, and some flavonols. In the second study, a comparison was made between the phenolic profiles of lentil seed coats that do not express the Tgc phenotype (genotype Tgc tan) and those that express Tgc (genotype Tgc Tan). The LC-MS analysis detected several compounds that were not influenced by tan, notably the phenolic acids, flavones, some flavonols, and some of dihydroflavonols. In contrast, myricetin, dihydromyricetin, and flavan-3-ols, and proanthocyanidin oligomers were detected only in Ggc Tgc Tan lines and therefore appear to be controlled by tan. The molecular analysis showed that tan is a basic-helixloop- helix (bHLH) transcription factor that could interact with the regulatory genes in the phenylpropanoid pathway for the enzymes flavonoid-3’,5’-hydroxylase (F3’5’H) and dihydroflavonol reductase (DFR). The third study measured the effect of long term storage on specific changes in phenolic compounds in lentil seeds. Increases in phenolic acids and flavones occur in green lentil seeds during storage, possibly because of the breakdown of more complex species into smaller subunits. More interestingly, a significant decrease in 27 flavan-3- ols and proanthocyanidins also occurs. Polymerization of flavan-3-ols and proanthocyanidins and their conjugation to cellular constituents could reduce their extractability and produce dark pigments in long stored lentil seeds. In conclusion, these studies determined that there is a relationship between phenolic compounds, specifically flavan-3-ols and proanthocyanidins, and seed coat colour genes tgc and tan in lentil. The findings of this study will help to develop future breeding strategies for lentil cultivars with aesthetic properties and nutritional benefits that appeal to consumers.