Characterization of Hakea sericea Fruits Regarding Chemical Composition and Extract Properties

The chemical composition and anatomy of the woody follicles of the hakea fruits are characterized here for the first time, aiming at an appraisal of their potential valorization. Hakea sericea Schrader is a woody shrub with evergreen needle-like leaves and fruits composed of woody follicles that surround the seed. The woody follicles have two dehiscent valves containing a primary and a secondary wood growth distinguished by dark and pale color respectively. H. sericea was introduced as an ornamental and hedge plant but it became a major problem due to its invasive character. The woody follicles of the hakea fruits had the following chemical composition (dry mass): ash 1.1%, total extractives 7.4% mainly corresponding to polar compounds soluble in ethanol and water, lignin 29.0% and 62.6% polysaccharides. The polysaccharides showed a predominance of xylose (43.2% of total monosaccharides) and glucose (40.5%). The mineral composition of the hakea fruit contains substantial amounts of potassium. The main lipophilic extractives are bilobol derivatives (23.9–41.8% of the extract), alkanols (15.5–26.5%) and saturated alkanoic acids (10.6–13.1%). The ethanol–water H. sericea fruit extract contains total phenolics (186.3 mg GAE/g extract), flavonoids (67.7 mg CE/g extract) and condensed tannins (84.9 mg CE/g extract). The antioxidant activity was weak compared to known antioxidants (271.7 mg Trolox/g extract). H. sericea fruits fracture easily with predominance of larger particles and little formation of fines (5.8% of the total mass). The chemical characterization of different granulometric fractions showed that extractives were present preferentially in the finest fractions, particularly with enrichment in ethanol soluble compounds, with the exception of bilobol derivatives that were present in higher amounts in fines. Most promising valorization routes for the hakea fruits include a fractionation process for hemicelluloses to yield potentially valuable xylo-oligosaccharides (XOS) and the recovery of bilobol derivatives from the lipophilic extract given the potential application of these compounds in medicine.