Determination of hydroxylated fatty acids from the biopolymer of tomato cutin and their fate during incubation in soil

Introduction - The plant cuticle is a thin, predominantly lipid layer that covers all primary aerial surfaces of vascular plants. The monomeric building blocks of the cutin biopolymer are mainly ω-hydroxy fatty acids.Objective - Analysis of ω-hydroxy fatty acids from cutin isolated from tomato fruits at different stages of decomposition in soil. Different derivatives and mass spectrometric techniques were used for peak identification and evaluation.Methodology - Preparation of purified cutin involving dewaxing and HCl treatment. Incubation of purified cutin for 20 months in soil. Pentafluorobenzoyl derivatives were used for GC/MS operated in the electron capture negative ion (ECNI) mode and trimethylsilyl ethers for GC/MS operated in the electron ionisation (EI) mode for analysis of ω-hydroxy fatty acids.Results - Six ω-hydroxy fatty acids were detected in the purified cutin, three of which were identified as degradation products of 9,16-dihydroxyhexadecanoic acid as a consequence of the HCl treatment involved in the purification step. Incubation of the isolated cutin in soil was accompanied with decrease in concentration of all hydroxyl fatty acids.Conclusion - We produced evidence that the HCl treatment only affected free hydroxyl groups and thus could be used for proportioning free and bound OH-groups on cutin fatty acids. The method enabled a direct quantification of the ω-hydroxy fatty acids throughout the incubation phase.