Relationship Between γ-Glutamyl Transpeptidase, Alliinase And Garlic Greening

Garlic, Allium sativum L., is the perennial herb of lily family. The bulb of garlic has high nutrition and medicine value. The yield of garlic in China is 76 percent of the whole world and garlic is often made into different kinds of products, such as garlic puree, garlic juice, dehydrated garlic slice garlic powder and so on. But garlic usually becomes green in the manufacture of puree and the products are damaged in both appearance and quality. So it's of great significance to study garlic greening. In this article, the activity ofγ-Glutamyl transpeptidase and alliinase, and the ability of garlic greening in different staorage conditions were studied.γ-Glutamyl transpeptidase was separated and purified successfully from garlic bulb, and its properties were studied. Amino acid composition of garlic in different periods was researched. Relationship betweenγ-Glutamyl transpeptidase, alliinase,amino acid and garlic greening was confirmed. The main study results were as follows:1. Change of enzyme activity and garlic greening ability at different storage. Low temperature was an important factor of activating alliinase and garlic greening. The activity ofγ-Glutamyl transpeptidase was corresponding to the ability of garlic greening during storage period. Alliinase played a very important role in garlic greening.2. Separation and purification ofγ-Glutamyl transpeptidase.γ-Glutamyl transpeptidase was purified up to 14.39 times with a recovery of 19.4% by the method of ammonium sulfate precipitation, Hydrophobic Interaction Chromatography, ConA-Sepharose chromatography column.γ-Glutamyl transpeptidase in sequence. The relative molecular weight ofγ-Glutamyl transpeptidase was 68,000 and its two subunits was 54,000 and 14,000 respectively.γ-Glutamyl transpeptidase had a carbohydrate content of 11.31%. The glycosidic linkage was inferred to be N-type byβ-elimination test. The maximum absorption spectra was about 275nm.3. Properties ofγ-Glutamyl transpeptidase. Kinetic characteristics ofγ-Glutamyl transpeptidase were as follows: the Km was 10.83 mmol/L and Vmax was 28.65u/L under the optimum conditions. The enzyme-catalyzed reaction rate ofγ-Glutamyl transpeptidase had a good linear relationship with time between 30～180min, and the optimal conditions of reaction time was 30min. Its optimum pH and temperature was 8.5 and 42oC respectively. It was stable comparatively at pH value of 6~7 and temperature lower than 50oC. Ca2+, Mg2+ had better activation effect onγ-Glutamyl transpeptidase than Al3+, K+, Na+. Other metal ions such as Fe2+, Fe3+ were the inhibitive factors ofγ-Glutamyl transpeptidase activity.4. Verification test of garlic greening. The experiment proved thatγ-Glutamyl transpeptidase did not participate in the generation of garlic green pigment. It was possible thatγ-GTP involved in physiological and biochemical response, then garlic could green when secondary products accumulated in some degree. Alliinase took part in the process of garlic greening. It proved that amino acid did not cause greening of the fresh garlic by external simulated test.