Cooking quality of faba bean after storage at high temperature and the role of lignins and other phenolics in bean hardening

Selected physical and chemical characteristics of faba beans (Vicia faba L.) cv. Fiesta were studied after 12 months storage at 5, 15, 25, 37, 45 or 50 °C (±2 °C) in relation to the hard-to-cook phenomenon. In comparison with control (seeds stored at 5 °C), seeds stored at 15 and 25 °C demonstrated non-significant (p⩽0.05) changes in most of the physical and chemical characteristics including hydration and swelling coefficients, acid detergent fibre, lignin and tannin contents, whereas seeds stored at ⩾37 °C demonstrated significant changes (p⩽0.05). Solutes and electrolytes leaching after 18 h soaking substantially increased with increased temperature. Faba bean hardness tested by the hard-to-cook test also increased substantially with increased storage temperature. After 8 h soaking followed by 2 h cooking, the puncture force required for seeds stored at 5 °C was 3.3 N seed−1 whereas seeds stored at 50 °C required a much higher puncture force of 15.2 N seed−1. There was a high negative correlation (r2=0.98) between storage temperature and cooking ability of faba bean. Substantial increases in acid detergent fibre and lignin contents occurred with increased storage temperatures. There was a three-fold increase in lignin content of faba bean stored at 50 °C compared to those stored at 5 °C and it was correlated with bean hardness (r2=0.98). Storage at high temperatures for 12 months led to a substantial reduction in total free phenolics especially in the testa and there was a greater reduction with increasing storage temperature. Reduction in free phenolics was negatively correlated (r2=0.75) with bean hardness.