Evaluation of lipoxygenase activity in common beans by UV and NMR spectroscopy: proposal for a complementary technique for enzymatic studies

Abstract

Factors that reduce the quality of common bean during storage, including oxidative rancidity caused by lipoxygenase, have been extensively studied. In this context, this work evaluates lipoxygenase activity in five Carioca bean cultivars at different temperatures and storage times using ultraviolet (UV) and nuclear magnetic resonance (NMR) spectroscopies. UV absorption analyses demonstrated that the storage temperature of the grains influences the kinetic reaction rates during the enzymatic activity of lipoxygenase. Pinto beans and CNFC 10467 presented lower initial activity than the three BRS varieties but were more sensitive to high temperatures. BRS Estilo presented an anomalous behavior, with a strong reduction in activity at 15 and 21 °C until 72 days of storage. BRSMG Madrepérola and BRS Pontal presented stable enzymatic rates until 108 days of storage. A 26% reduction in fatty acid content, as a result of lipoxygenase action during storage, was observed both in solution-state and high resolution magic angle spinning (HR-MAS) NMR studies. These results highlight the importance of NMR in enzymatic kinetic reactions studies, complementing the results obtained by UV.