Inhibitory Effect of Onion Oil on Browning of Shredded Lettuce and Its Active Components

Abstract

The effect of onion oil on the prevention of browning of shredded letuce was examined and its inhibitory components sought. It is not necessary for the oil to be in direct contact with shredded lettuce to inhibit browning, the active components are believed to be volatile. GC-MS analysis revealed that the main components of the onion oil were dipropyl trisulfide, dipropyl disulfide and methyl propyl trisulfide. Although the active fractions were widely dispersed in the high performance liquid chromatogram when the browning inhibitory effect of each fraction was tested by the fractionation of the onion oil, the dipropyl trisulfide fraction was the most inhibitory, followed by methyl propyl trisulfide fraction, dipropyl disulfide fraction and propyl propenyl disulfide fraction in the weakening order. Among the tested components, dimethyl trisulfide possessed the strongest specific activity, but its quantity was very small. These results suggest that inhibition of browning of shredded lettuce is mainly due to the main components of onion oil and that trisulfides are more inhibitory than disulfides.