44C-2 |
Lipoxygenase from Banana Leaf: Purification of an enzyme that catalyzed the oxygenation of linoleic acid at 9-position. |
J. M. KUO1, A. Hwang, H. C. Wu, H. L. Chu, and D. B. Yeh. (1) Dept. of Food Health, Chia-Nan University of Pharmacy and Science, 60, Erh-Jen Road, Section 1, Jen-Te Hsiang, Tainan Hsien, Taiwan, R.O.C., Tainan, 717, Taiwan In recent years there has been an increased interest in the production of natural flavor compounds via lipoxygenase (LOX) pathway. Briefly, the polyunsaturated fatty acid are converted to hydroperoxide by LOX action and further cleaved by hydroperoxide lyase (HPL) into C6 and C9 aroma compounds. For example, the C6 compounds (green character) could be derived from linoleic acid treated with soybean LOX oxygenated 18:2 at 13-position while the C9 compounds (melon, cucumber flavor note) could be formed from tomato LOX oxygenated 18:2 at 9-position. Most of the plant LOX oxygenated 18:2 at the position similar to that of soybean LOX, ie. predominately at 13-position or 9-&13-position with different ratio. In this study, we purify and characterize a LOX catalyzed the oxygenation of linoleic acid at 9-position from banana leaf. The LOX from banana leaf (Giant Cavendishii, AAA) were isolated and purified 326-fold using 25-50% saturation of ammonium sulfate fractionation, hydroxyapatite column separation, and gel filtration on Superdex 200. MW of the purified LOX was 85 kD. The optimal pH of the LOX was 6.2, and optimal temperature was 40 oC. The LOX showed the highest reactivity toward 18:2 followed by 18:3, 20:4, 22:6 and 20:5. Based on retention time in normal phase HPLC, the products of 18:2 reacting with the purified LOX were 9-HpODE (hydroperoxyoctadecadienoic acid), that from 18:3 was 9-HpOTE (hydroperoxyoctadecatrienoic acid). When the Triton X-100 was not added in the extraction media, no LOX activity was detected. It seems that LOX from banana leaf was a membrane-bound enzyme. The present study demonstrates very high LOX activity found in the banana leaf. Thus, the banana leaves are able to be used as a source of LOX to produce aroma compounds with melon, cucumber flavor note.
Session 44C, Fruit & Vegetable Products: Chemistry
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