Cloning of γ-Glutamyl Transpeptidase in Garlic Cloves and Relationship Among γ-Glutamyl Transpeptidase and Alliinase Activity, Storage Condition, and Garlic Blueing

Garlic blueing occurs when garlic cloves are stored at low temperature with increasing of 1-propenyl cysteine sulfoxide which is related with γ-glutamyl transpeptidase (GGT) and alliinase. Although garlic γ-glutamyl peptide metabolism is important in biosynthesis of blue pigment in crushed garlic, garlic GGTs are poorly characterized. We cloned the partial-length coding region of garlic GGT by homology with onion enzyme. We also stored garlic at 20^oC for 3 months (A), stored garlic at 20^oC for 3 months then transferred to 0^oC for 3 months (B), and stored garlic at 0^oC for 3 months then transferred to 20^oC for 3 months (C) to investigate relationship among GGT and alliinase activity, storage condition, and garlic blueing by RT-PCR. Results showed GGT activity increased in treatment B followed by storage at 0^oC for 3 months, and decreased in treatment C followed by storage at 20^oC for 3 months, whereas alliinase activity was not affected by storage temperature. It indicated that blueing in crushed garlic was affected by storage temperature with increasing GGT activity, not alliinase activity.