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Bark-based biorefineries: anatomical and chemical characterization of the bark of endemic Quercus vulcanica of Turkey

Publication . Şen, Ali Umut; Simões, Rita; Yücedağ, Cengiz; Quilhó, Teresa; Sousa, Vicelina; Miranda, Isabel M.; Fernandes, Ângela; Pereira, Helena

The detailed anatomical and chemical features of the bark from endemic Quercus vulcanica in Turkey are reported here for the first time and discussed in the perspective of integration into a bark-based biorefinery system. The bark of Q. vulcanica trees was collected and studied through observations using light and scanning electron microscopy, wet-chemical analysis, inorganic elemental and FTIR analyses, GC-MS determinations of lipophilic extractives and suberin monomers, as well as TBARS antioxidant activity of hydroethanolic extracts. The bark of Q. vulcanica comprises phloem and a rhytidome with thin periderms and a few cork layers. The ash content is high (16.4%), primarily consisting of calcium oxalate crystals. Extractives were present in a high amount (23.1%) of which 88% corresponded to hydrophilic extractives (10.3% ethanol, and 10.1% water solubles). The suberin content is low (3.7%), which aligns with the small proportion of cork in the bark rhytidome. The composition of suberin is characterized by similar proportions of alpha, omega-alkanoic diacids and omega-hydroxyalkanoic acids, with 18-hydroxy-9-octadecenoic acid (26% of monomers) and octadec-9-enedioic acid (20.6%) as the main monomers. The lignin content is 21.9%, and the monomeric composition of polysaccharides includes glucose, xylose, arabinose, galactose, rhamnose, and acetyl groups. The lipophilic extractives are mainly composed of terpenoids (72.2% of all compounds), with friedelin and friedelanol as the main compounds. Hydroethanolic extracts, obtained under mild conditions with a yield of 10.2%, exhibited antioxidant activity (TBARS assay, EC50 value of 55 mu g/mL). The overall chemical and structural properties of Q. vulcanica bark indicate promising potential for biorefineries.

2024Journal article

Open access

Biochemical characterization and fuel properties of endemic taurus flowering ash (Fraxinus ornus subsp. cilicica) bark from Turkey

Publication . Şen, Ali Umut; Simões, Rita; Yücedağ, Cengiz; Miranda, Isabel M.; Fernandes, Ângela; Pereira, Helena

Taurus flowering ash (Fraxinus ornus subsp. cilicica) is an endemic tree species in Turkey. The bark of the species was characterized for summative chemical composition, the monomeric composition of polysaccharides, phenolic content, in vitro and ex vivo antioxidant properties of hydrophilic extracts, the composition of lipophilic extractives and suberin, and thermal degradation. The bark has an elevated ash content (17%), primarily composed of calcium, and a noteworthy extractive content (38.9%), predominantly of hydrophilic compounds. The antioxidant activity of the bark extracts is moderate, with an IC50 value of 40 g/mL and an EC50 value of 230 g/mL by DPPH and TBARS methods. The lipophilic extractives principally contain fatty acids and diterpenoids. The suberin content is low (1%) and composed primarily of !-hydroxy acids with 9,10,18 trihydroxyoctadecanoic acid as the major suberin monomer. The lignin content is low (9.8%), and polysaccharides represent 33%. The ignition temperature of the bark is 190 C, the burnout temperature is 653 C, and the activation energy in combustion is 29 kJ mol􀀀1. A biorefinery concept was developed considering the bark’s chemical and thermal characteristics to convert approximately 90% of the bark mass into valuable chemicals, extracts, functional materials, and additives.

2023Journal article

Open access