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Kinetic study of enzymatic a-galactoside hydrolysis in cowpea seeds

Coffigniez F., Briffaz A., Mestres C., Ricci J., Alter P., Durand N., Bohuon P.. 2018. Food Research International, 113 : p. 443-451.

DOI: 10.1016/j.foodres.2018.07.030

The endogenous alpha-galactosidase activity of cowpea seeds was characterized and modelled assuming Michaelian behavior. The aim is to use the resulting knowledge to optimize alpha-galactoside degradation during the soaking-cooking process. In this study, the alpha-galactosidase enzyme from Wankoun cowpea was extracted and its enzymatic activity was analyzed as a function of temperature, pH and the presence of some inhibitors. Enzymatic activity was optimal around 35¿°C and a pH of 5.8. Activation and inactivation energy was evaluated at 50¿±¿3 and 103¿±¿9¿kJ.mol-1, respectively. The strongest inhibitor was galactose with an inhibition constant KI of 0.28¿±¿0.03¿mM. Incubation of the enzyme extract with alpha-galactosides revealed a 10-h lag phase in the early stages that could be due to low pH, the action of inhibitors including galactose and the biosynthesis of alpha-galactosides. After the lag phase, the degradation of each alpha-galactoside occurred without the appearance of any intermediary product. The degradation of alpha-galactosides was observed with a Km of 1.7¿±¿0.3¿mM for raffinose; 3.6¿±¿0.6¿mM for stachyose and 15.9¿±¿0.1¿mM for verbascose. A long soaking step around 35¿°C is suggested to maximize the alpha-galactosides enzymatic degradation.

Mots-clés : niébé; enzyme; biosynthèse; cuisson

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