Waxes composition of reproduction cork from Quercus suber and its variability throughout the industrial processing
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The chemical composition of waxes was studied in cork planks from three different trees of Spanish Quercus suber at four different stages of the industrial processing of the first transformation: stripping, first rest, boiling followed by open air rest and boiling followed by store-room rest. Waxes were extracted with chloroform (CHCl3) and the extract was submitted to saponification in order to obtain the neutral and acid fractions. The trimethylsilyl derivatives of both fractions were analysed by GC-MS. An important decrease of the total content of waxes -CHCl3 extract-(average values: 10.13 to 4.91%) and of the acid fraction (average values: 2.51 to 0.96%) was observed throughout the industrial processing. Some differences were also found among trees, two of them being richer in total waxes (average, 8.14 and 7.71%) than the other one (average, 4.67%). Concerning the three groups of identified components (fatty acids, fatty alcohols and triterpenes), the contents of the fatty alcohols and acids suffer an important reduction during the first rest (average values: 30.39 to 17.53% and 58.73 to 31.48%, respectively), while after boiling, there is a decrease of the triterpenes concentrations (79.16 to 58.00% -neutral fraction- acid 40.23 to 23.20% -acid fraction-), being greater when the second rest is carried out in a store room. Significant differences among trees were only found in the fatty alcohols contents. The neutral fraction was mainly composed by fatty alcohols tall the even members from C-18 to C-26, With traces of intermediate odd members and some unsaturated groups, C-20 and C-21) and triterpenes (14 components, among them friedelin, betulin and cerin were identified), and a very small amount of monocarboxylic fatty acids (C-16, C-18, C-22 and C-24 members) was also present. The main group of components of the acid fraction was that of fatty acids (saturated even C-12-C-24 and odd C-15, C-17, C-21 members, accompanied by a great amount of unsaturated terms and some omega-hydroxyacids, 18-hydroxy-9,12-octadecadienoic and 18-hydroxy-9-octadecenoic acids). Four triterpenes, the C-20, C-24 and C-28 alcohols and ferulic acid were also detected in the acid fraction. Some of these individual components of each fraction were also affected by the industrial processing and presented significant differences among the studied trees.
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