Faba bean (Vicia faba L.) seeds darken rapidly and phenolic content falls when stored at higher temperature, moisture and light intensity

Faba beans cv. Fiesta with seed moisture content (SMC) modified to 8, 10, 12 and 14% were packed in polyethylene lined aluminium foil bags and stored at 5, 15, 20, 25, 30, 37, 45, 50 or 60 °C (± 2 °C) for one year. Samples were analysed for moisture content and seed coat (testa) colour over the storage period using a chroma meter. A continuous increase in L∗ and b∗ values was found in all samples with the passage of time whereas a∗ values first increased and then decreased in samples stored at relatively high temperatures (≥ 37 °C). The initial beige testa colour changed to light brown, dark reddish-brown or almost black depending on storage conditions. The higher the temperature and SMC the faster the rate of change in colour (▵Eab∗ values). Seeds with 8% SMC had more stable testa colour compared to seeds with higher SMC. Exposure to artificial light (350 μ mol m−2 s−1) substantially accelerated the colour darkening. Cotyledons stored at 37 ± 2 °C also darkened with the storage time. A loss in total free phenolics, total tannins and proanthocyanidins was found with increased darkness of testa and cotyledons during storage.