Studies On The Extraction, Isolation And Identification Of Glycosidically Bound Aroma Components In Six Kinds Of Fruits

Aroma compounds in plants include free and bonding states. Glycosidically bound aroma precursors, as a class of latent fragrant components, widely exist in natural plants and can be released by enzymatic hydrolysis in the process of plant maturation. Compared to the free aroma substance, bound form aroma precursors are more stable, and have important research significance and broad application prospects. In this thesis, the bound aroma compounds in six common kinds of fruits have been studied and the qualitative and quantitative analysis and comparison have been conducted. Among them, the glycosidically bound aroma precursors in red Fuji apple are deeply studied. As a result, six kinds of contained glycosides are separated and the exact structures are identified for the first time. The main research contents and results are as follows:1. The references about glycosidically bound aroma precursors were reviewed, including the research methods, extraction and separation methods, and research progress at home and abroad. The research significance and the content of this paper were expounded on this basis.2. The free and bound aroma constituents in red Fuji apple were effectively separated by the method of Amberlite XAD-2 resin adsorption and ether/pentane mixture and ethanol elution. After enzymolysis on the bound aroma compounds, qualitative and quantitative analyses were achieved by GC-MS. Sixteen kinds of free volatiles and seventeen kinds of bound aroma components were identified, respectively. Among them,2-Methoxy-3-(2-propenyl)phenol,3-(4-methoxyphenyl)-1-propanol, and 2’-hydroxyl-4’,5’-dimethylacetophenone were first found as bound aroma volatiles in apples.3. Six glycosidic aroma precursors were tentatively identified by GC-MS analysis of trifluoracetylated derivatives of ethanolic elution in red Fuji apple. To obtain the pure glycosidic bound aroma compounds in red Fuji apple, ethanolic elution was successively separated and purified by low-pressure preparative liquid chromatography, high-pressure preparative liquid chromatography and HPLC methods. Finally, six glycosidic compounds were isolated from 45kg Fuji apples and identified with NMR and MS characterization techniques for the first time. Among them,6,9-dihydroxy-4,7-megastigmadien-3-one-9-O-[β-D-xylopyranosyl-(1â†'6)]-β-D-glucopyranoside, 1-phenalethanol-O-[a-D-araopyranosyl-(1â†'6)]-β-D-glucopyranoside and 2-O-β-D-xylpyranosyl-3-methyl-4-phenyl-2,6-hexanediol-6-O-α-L-rhamnopyranosyl-(1â†'6)-β-D-glucopyranoside were proved to be new compounds.4. Under the same experimental conditions, the bound aroma compounds in pineapple, strawberry, pear, orange and red grape were hydrolyzed, identified by GC-MS and analysed quantitatively. The common and unique aroma components in these five kinds of fruits were compared and discussed.