Reactions of isothiocyanates with food proteins: Influence on enzyme activity and tryptical degradation

Abstract

This paper deals with the interactions of isothiocyanates (ITC) with different plant proteins (legumin from faba beans and bromelain). The derivatives formed with benzyl and phenyl-ITC have been characterised in terms of their solubility, free £-amino groups, as well as in the amount of carbon disulphide liberated during acidic hydrolysis as an indication for a reaction at the sulfhydryl groups of the proteins. A decrease in solubility and in the amount of free £-amino groups coupled with an increase in the hydrophobicity was observed. Further the isoelectric points were shifted to the lower pH values (e.g. for bromelain, the isoelectric point was changed from about pH 10 to values between 7 to 9). The isoelectric focussing of legumin under non-reducing as well as under reducing conditions also showcd a clear shift of the isoelectric points of it's components. The enzymatic activity of bromelain decreased indicating a reaction has taken place at the sulfhydryl groups, one of which is located in the active centre of the enzymc. The tryptic degradation of the legumin ITC derivatives was found to be negatively influenced.