A methodological approach for the simultaneous quantification of glycerol and fatty acids from cork suberin in a single GC run

Introduction: Suberin, as part of plant protective barriers, is one of the most important natural Polymers after cellulose and lignin. For a full elucidation of suberin structure the quantification of glycerol, fatty α,ω-diacids and ω-hydroxyacids, the major building blocks of suberin, is of primary importance. Glycerol is often lost in the most used analytical procedures or rarely determined by deficient or too laborious techniques.

Objectives: Propose a simple, accessible and reliable methanolysis work-up procedure for an accurate and simultaneous quantification of glycerol and suberin fatty monomers in the same GC run.

Material and methods: Cork from Quercus suber L. was depolymerised by methanolysis. Glycerol was derivatised to an organic soluble form before the suberin monomers recovery in water/organic solvent partition. Gas chromatography flame ionisation detector (GC-FID) response factors were determined for glycerol, ferulic acid and one for each fatty monomer substructure. Additionally, 1,2,4-butanetriol and methyl nonadecanoate were used as internal standards.

Results: The proposed experimental approach allowed the glycerol and all the fatty suberin monomers in the same GC run to be quantified accurately. Glycerol represented 30.6 area%, 14.2 mass% and 38.4 molar% of suberin and the COOH/OH groups ratio was 0.6:1 in the proposed experimental approach in contrast with 0.10 area% and COOH/OH ratio of 3:1 in the most used protocol. Furthermore, ω-hydroxyacids/α,ω-diacids mass ratio was 1:1 as opposed to an area ratio of 1.5:1.

Conclusion: The proposed work-up procedure revealed to be a reliable analytical tool for the complete analysis of suberin allowing the future knowledge to grow towards a better understanding of suberin structure throughout its range and variability.

GC-FID; cork; glycerol; response factors; suberin.