Storage Temperature and Grain Moisture Effects on Phenolic Compounds as a Driver of Seed Coat Darkening in Red Lentil

The biochemistry underlying seed coat darkening of lentil due to extended storage is limited. This study investigated the relationship between seed coat darkening over time during storage and changes in concentration of phenolic compounds (total phenolic compounds, total condensed tannins, proanthocyanidins and anthocyanins) in two red lentil cultivars (PBA Hallmark and PBA Jumbo2), stored at two grain moisture contents (10 and 14%, w/w) and two temperatures (4 and 35 °C) for 360 days. Seed coat darkening was only significant (p = 0.05) at high temperatures (35 °C) but not at low temperatures (4 °C), irrespective of grain moisture content and cultivar. The concentration of all phenolic compounds tested in this study reduced significantly (p = 0.05) throughout the study period, regardless of temperature and grain moisture treatments. The changes in seed coat brightness and redness followed a linear pattern, except for yellowness, where phenolic compounds initially reduced linearly and then remained constant thereafter. Darkening of seedcoat was only associated with the reduction in phenolic compounds tested in this study at 35 °C, and not at 4 °C. This suggests that seed coat darkening due to extended storage may not be directly linked to broad reductions in the groups of phenolic compounds or individual compounds assessed in this study. This information prompts further research to identify the actual biochemical processes that cause the darkening of seed coats during storage and assist in developing cultivars with stable seed coat colour by selecting and modifying such processes.