Chemical characterization of the bark of Eucalyptus urophylla hybrids in view of their valorization in biorefineries

Abstract

Eucalyptus urophylla hybrids are important raw materials for the forest industry in Brazil, and large quantities of barks are available at mill site that may be used for added-value products. The chemical composition of barks of six commercial hybrids clones of E. urophylla×E. grandis, E. urophylla×E. Camaldulensis, and undisclosed E. urophylla hybrids was studied. The hybrids had similar composition, on average (data based on oven dry bark): 16% extractives, mainly corresponding to polar compounds that are soluble in ethanol and water, 19% lignin, 47% polysaccharides, 1% suberin, and 2% ash. The polysaccharides consists mainly of cellulose as indicated by 84% of total neutral monosaccharides in the acid hydrolysate and 10% xylose. The compositions of the lipophilic extracts was determined by GC-MS before and after alkaline hydrolysis. In all the barks, fatty acids, and triterpenes (namely: betulinic and ursolic acids) were the most abundant compounds followed by smaller amounts of sterols, long-chain aliphatic alcohols, phenolic acids, and acylglycerols. The ethanol-water bark extract had a high phenolic content: total phenolics ranged 211–551 mg gallic acid equivalents (GAE) g-1 of extract, tannins 76–184 mg catechin equivalents (CE) g-1 extract, and flavonoids 98–234 mg CE g-1 of extract. The antioxidant activity corresponds to 338 mg Trolox g-1 of extract. Development of high-value products is proposed through an integrated biorefinery approach including valorisation of extractives and targeting for cellulose-based applications.