Studies On The Isolation, Purification And Structure Of The Pigment In Greening Garlic

Garlic(Allium Sativum L.)is liliaceous plant, the bulb of garlic is rich in nourishment including protein, carbohydrate, fat, vitamin and mineral element such as Ca,P,Fe,Se,Ge and so on. China is a huge producing country of garlic whose yield occupy 76 percent of the whole world. Garlic is often made into different kind of products except eating in fresh. But garlic always becomes green in the process and has bad effect on character, so it is in great need to solve this problem. Garlic green pigment was separated and purified by the methods of solid phase extraction (SPE), macroporous adsorption and gel filtration chromatography. The green pigment was characterized by liquid chromatography-mass spectrum(LC-MS) , nuclear magnetic resonance(NMR) spectroscopy, and infrared spectrum(IR). The light stability of garlic green pigment was also studied to offer theoretical basis for mechanism of garlic greening.1. Isolation and purification of the green pigment Method of HPLC to isolate and detect the pigment was established. The detecting conditions were that: Alltech Alltima C18 column (250mm×4.6mm), mobile phase: acetonitrile:water = 2:8 (0.1% formic acid), column temperature: 30℃, detection: UV at 440 nm, flow rate: 1.0mL/min.Garlic green pigment was separated and purified by a series of column chromatography, and the purity of green pigment was tested by the methods of HPLC. The purification procedures were as follows: let the raw green extracts passed XAD-16 macroporous resin adsorption firstly, 0.2%HCl methanol as the elution solvent,1BV/h as the flow rate. The green outflow was then passed Sephadex LH-20 gel resin, methanol as the elution solvent, 1.2BV/h as the flow rate on desorption to achieve high purification.2. Molecular weight mensuration and structure identification of the green pigment The LC-MS result showed that the MW of green pigment was 527. Purified solid of green pigment was obtained to identify structure through NMR and IR. NMR spectrum showed that green pigment:①contain pyrrole ring which substituent contain H;②contain unsaturated carbon such as C=C;③contain-CH3. IR spectrum showed that green pigment:①belong to aromatic heterocyclic compound, conjecture it be pyrrole derivatives containing N;②contain -CH3,-OH ,C=C&C=S. 3. Light stability of the green pigment The effect of different light factors on the stability of green pigment was studied using UV-visible spectrophotometric methods. The results showed that green pigment had a little stability under light. The effect of outdoor natural light and ultraviolet light was obvious to the stability of green pigment, and ultraviolet light had destructive effect on it. Green color went away while yellow color presented in the sample.