Effect of supercritical carbon dioxide on the decomposition products of glucosinolates and myrosinase activity

There is a growing need in the food industry to inactivate enzymes remaining in food products. These enzymes cause unpleasant changes and degrade food quality during storage and distribution. There is also a need to isolate the biologically active constituents in food products. There is also a desire in the biotechnology industry to explore the use Of SC-CO2 as an enzymatic reaction medium, an alternative to organic solvents. The effect of supercritical carbon dioxide (SC-CO2) on myrosinase activity was studied. To better understand the behavior of myrosinase in SC-CO 2, myrosinase was isolated from yellow mustard seeds and subjected to SC-CO2 treatment under various conditions. The SC-CO2 parameters investigated were temperature, pressure, exposure time, moisture, and modifiers. The experimental data showed that the enzymatic activity of isolated crude myrosinase was significantly affected (P < 0.05) by increases in temperature. Pressure changes in the range of 6.8--24.3 MPa and exposure time did not have significant effect on myrosinase activity (P > 0.05). A combination of moisture (ca. 26%) and SC-CO2 treatment at 60°C and 24.3 MPa for 10 min resulted in a 96% reduction of myrosinase activity in mustard seeds. No significant change in enzyme activity was observed at moisture level of ca. 7%. Myrosinase activity in a crude enzyme extract was retained after addition of 4% to 6% (v/v) modifiers such as ethanol, phosphate buffer, water, and ion-pair reagent under SC-CO2 conditions of 24.3 MPa and 35°C. SFE recovery studies were performed for two enzymatic hydrolysis products of sinigrin before investigating the mechanism of myrosinase activity loss under SC-CO2 conditions of 24.3 MPa and 35°C. Percent recoveries of 95% +/- 5% and 96 +/- 5% were obtained for allylisothiocyanate and allylcyanide respectively. Allylisothiocyanate was the only product formed after myrosinase hydrolysis reaction of sinigrin in a non-SC-CO2 conditions at pH 6.5. Whereas, both products were formed after in-situ ion-pairing enzyme hydrolysis reaction of sinigrin in SC-CO2 conditions. Reduction in pH was not the cause of myrosinase activity loss due to the SC-CO 2 treatment.