Purification and Characterization of γ-Glutamyl Transpeptidase from Toona sinensisand Its Function on Formation of Sulfur-Containing Volatiles

γ-Glutamyl transpeptidase (GGT) in Toona sinensis shoot (TS) was extracted and purified through salt precipitation, ion-exchange column, and gel filtration chromatography methods. The GGT had two peptides with M.W. 35 and 50 kDa. Its function in the formation of TS sulfur-containing volatiles (SCVs) was evaluated. The highest GGT hydrolytic activity was at pH 7.0 and 50 °C. Its activity was enhanced by Ca2+, Mg2+, K+, Na+, and Ba2+ and reduced by Cu2+, Fe3+, Mn2+, and Zn2+. The SCVs reached the highest level at GGT to TS sulfur-containing precursors extract 1:20. The aroma produced by GGT from the extract was similar to that of raw TS, especially for the cooked onion-like/TS-like flavor. These results revealed the characteristics and function of GGT in TS on sulfurous aroma formation. It could be applied to retrieve the production of sulfur-containing aroma from thermally preserved TS or similar vegetables, which lost GGT activity irreversibly during heat drying.