The chemical composition and cellular structure of corks from cork oak (Quercus suber) trees grown in Bulgaria and Turkey were studied for the first time to gain insight into the quality of cork from areas external to the species natural distribution. The cellular structural arrangement of Bulgarian and Turkish corks was similar to Portuguese cork, but chemical composition differed significantly. In general, Bulgarian and Turkish corks contained higher amount of ash and lignin and lower amount of extractives than Portuguese cork. Bulgarian cork contained less suberin and more polysaccharides than Turkish and Portuguese corks. The differences in the suberin/lignin ratio (1.4, 1.1 and 2.0 in corks from Bulgaria, Turkey and Portugal, respectively) suggest differences in mechanical behavior, namely in compression. Suberin composition was similar in all corks, but differences in relative proportion of families and compounds were present, indicating natural variation related to cork origin. Lipophilic extractives differed between corks: Betulinic acid was the main triterpene in Bulgarian cork, while friedelin dominated the lipophilic extractives in Portuguese and Turkish corks. A new lupane-type pentacyclic triterpene was found in Bulgarian and Turkish corks.
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