Cutin extraction and composition determined under differing depolymerisation conditions in cork oak leaves. Issue 1 (22nd June 2021)

• Record Type: Journal Article
• Authors: Simões, Rita; Miranda, Isabel; Pereira, Helena
• Is Part Of: Phytochemical analysis. Volume 33:Issue 1(2022)
• Page Start: 127
• Page End: 135
• Publication Date: 2021-06-22
• Subjects: alkaline methanolysis -- cutin fragmentation -- fatty acids -- glycerol -- macromolecular assembly -- Quercus suber leaves; Plants -- Analysis -- Periodicals; Plants -- chemistry -- Periodicals; 572.2
• DOI: 10.1002/pca.3075
• Languages: English
• ISSNs: 0958-0344

Abstract

Abstract: Introduction: Cutin is a biopolyester involved in waterproofing aerial plant organs, including leaves. Cutin quantification and compositional profiling require depolymerisation, namely by methanolysis, but specific protocols are not available. Objectives: Investigate how different methanolysis conditions regarding catalyst concentration effect cutin depolymerisation and monomer release, to better define protocols for cutin content determination and composition profiling. Material and Methods: Cork oak ( Quercus suber ) dewaxed leaves were reacted with five sodium methoxide (NaOMe) concentrations. Extracts were analysed: glycerol by high‐performance liquid chromatography (HPLC) and long‐chain lipids by gas chromatography–mass spectrometry (GC–MS). Results: Cutin was completely removed by 3% NaOMe (8.4% of dewaxed leaves), while mild 0.1% and 0.01% NaOMe methanolysis only depolymerised 14% of total cutin. Reactivity of cutin ester bonds is not homogeneous and glyceridic ester bonds are more easily cleaved, releasing the existing glycerol already under the mildest conditions (0.53% with 0.01% NaOMe and 0.41% with 3% NaOMe). The composition of cutin extracts varies with depolymerisation extent, with easier release of alkanoic acids and alkanols, respectively, 34.9% and 8.8% of total monomers at 0.1% NaOMe, while ω‐hydroxyacids (49.3% of total monomers) and α, ω‐diacids (9.0% of the monomers) are solubilised under more intensive reactive conditions. Conclusion: Cutin of Quercus suber leaves is confirmed as a glyceridic polyester of ω‐hydroxyacids and alkanoic acids, with minor content of α, ω‐diacids, and including coumarate moieties. The protocol for the determination of cutin content and compositional profiling was established regarding catalyst concentration. The molar composition of cutin suggests a macromolecular assembly based on glycerol linked to lipid oligomeric chains with moderate cross‐linking. Abstract : Cutin from Quercus suber leaves was depolymerised with different sodium methoxide (NaOMe) concentrations. Cutin was completely removed by 3% NaOMe (8.4% of dewaxed leaves), while incomplete solubilisation occurred with milder methanolysis (14% of cutin with 0.1% NaOMe). Reactivity of cutin bonds differs with glyceridic ester bonds being more easily cleaved, and all glycerol is released under the mildest conditions. Cutin extracts composition varies with depolymerisation extent with easier alkanoic acids and alkanols release, while ω‐hydroxyacids and α, ω‐diacids are solubilised with more intensive conditions.