Branched Polyesters from Depolymerisation of Tomato Native Cutin by Supercritical Water Hydrolysis: Advances in elucidating the Polyester Architecture of Cutin

Cutin is a structural biopolyesters that forms the scaffold of the plant cuticle, an insoluble and chemically resilient barrier at the plant–environment interface. Cuticle plays a crucial role in preventing water loss, regulating gas (CO₂, O₂) permeability, protecting against microbial invasion, shielding against ultraviolet radiation, and mitigating other environmental stressors. Tomato native cutin conventional valorization strategies rely on harsh chemistries that destroy its native polyester architecture, limiting mechanistic insight and material exploitation. Here we report an ultrafast depolymerization strategy based on supercritical water hydrolysis that enables complete conversion of native tomato cutin into soluble branched polyesters within 10.5 seconds. Precise control of residence time reveals a hierarchical cleavage mechanism in which secondary esters at branching points hydrolyze preferentially over primary backbone esters. Spectroscopic and chromatographic analyses (FTIR, NMR, GPC, GC–MS) confirm selective bond scission, progressive molecular weight reduction, and identify 10,16-dihydroxyhexadecanoic acid as the dominant monomeric unit and revealed 16-hydroxy-9Z-hexadecenoic acid as a novel SCW-specific product, formed via a carbocation-driven intramolecular dehydration pathway inaccessible under alkaline conditions. A structurally constrained network model derived from reactive group analysis depicts cutin as a heterogeneous crosslinked polyester dominated by 10,16-dihydroxyhexadecanoic acid, with glycerol acting as a branching node, multifunctional C18 hydroxy acids and α,ω-diacids as linkers, and fatty acids as chain terminators. Green metrics confirm the process achieves an E-factor of 0.8 kg waste kg product⁻¹ with water recovery, outperforming alkaline hydrolysis (E-factor 4.1) in mass efficiency. This process-intensified approach enables structural resolution of native cutin and establishes a scalable platform for plant polyester valorization.