Tomato (Solanum lycopersicum) leaf juice as enzyme source: a study on the impact of endogenous proteases on plant proteins

Resúmen

Tomato leaves are by-products of tomato production and can be considered as source of enzymes due to its endogenous proteolytic activity. The endogenous proteases can alter the functionality of other proteins. In this study, we investigated the effect of tomato leaf juice on the properties of a selected number of plant proteins, with focus on the endogenous proteases. The effect was analyzed at molecular scale using SDS-PAGE and HPSEC and at colloidal scale in terms of protein dispersibility, particle size distribution and viscosity. Lastly, the effects on the gelation behavior and rheological properties were characterized. We observed partial hydrolysis of all plant proteins under the tested conditions. The hydrolysis was specific for each protein and incomplete. The partial hydrolysis resulted in significant changes in protein dispersibility and particle size. For plant proteins with low protein dispersibility, dispersibility increased due to size reduction of the swollen particles. For plant proteins with high protein dispersibility, dispersibility decreased due to the formation of larger aggregates. The partial hydrolysis also resulted in small increase of viscosity, with exception of soy protein isolate, of which the viscosity decreased. Finally, the partial hydrolysis resulted in reduction of the least gelling concentration for all plant proteins, while some of the formed gels exhibiting higher gel strength than the corresponding water gels. This suggests that partial hydrolysis led to formation of more interactions, but these interactions were mostly weak. To conclude, our findings provided a comprehensive overview of the effects of tomato leaf juice proteases on plant proteins.