A Spectrophotometric Assay for Total Garlic Thiosulfinates Content. Kinetic Aspects of Reaction with Chromogenic Thiols

Garlic (Allium sativum) is a plant known for its antimicrobial, antithrombotic and antiatherosclerotic properties. Those features are attributed to thiosulfinates, compounds formed in an enzymatic reaction occurring during garlic cloves crashing. A spectrophotometric method for the determination of thiosulfinate concentration in garlic extracts and supplements was proposed. It is based on reactions between thiosulfinates and selected chromogenic thiol compounds: 2-mercaptopyridine (2-MP), 4-mercaptopyridine (4-MP), 1-oxide-2-mercaptopyridine (MPO), 2-mercaptopyrimidine (MPM) and 2-nitro-5-thiobenzoic acid (NTB). Then kinetics of the reactions was studied. Rate constants and orders were determined. All reactions are first order with respect to the thiol and first order with respect to TS so the reactions of all tested thiols with garlic TS run in accordance with second order kinetics. Reaction rates vary among the thiol compounds: the constant rates differ from 6.7 (mol/L)-1.min-1 for 2-MP to 1129 (mol/L)-1.min-1 for NTB. Knowledge of the kinetic equation for the reactions and measurements of the initial rates allowed determining thiosulfinate contents in garlic extracts and supplements.