Phenolic profiling of green lentil (Lens culinaris Medic.) seeds subjected to long-term storage

Lentils have several desirable properties that make them a healthy and nutritious food option. The visual characteristics of the seed coat are important factors that determine the marketability and, ultimately, the sale price of whole lentils. However, the seed coat colour is not stable and green lentil in particular is known to change over time. While total phenolic content is known to significantly affect darkening of lentil seeds, this study investigated the effect of specific phenolic compounds in the seed darkening process in detail. The phenolic compound profiles of six green lentil cultivars were examined by liquid chromatography-mass spectrometry. To maximize the potential amount of change, the oldest seeds available (harvested in 2000-2007) were compared with fresh seeds (harvested in 2014). Some increases in amounts were noted for some phenolic acids and flavones; however, the most notable result was a decrease in the amount of all flavan-3-ols (e.g. catechin, gallocatechin, and catechin-3-glucoside) and proanthocyanidins (e.g. dimers, trimers, tetramers, and pentamers), 27 compounds in total. Polymerization of these oligomers (the major phenolic compounds in green lentil seed coat tissue) results in their cross-linking with the cell wall. The consequence will be seed darkening and reduction in the extractability of these oligomers.