Exploring acorn shells: Phenolic composition and bioactive potential for sustainable valorization

Pedunculate ( Quercus robur L.), holm ( Quercus rotundifolia Lam.), and cork ( Quercus suber L.) oaks are abundant across the Portuguese landscape. This study aims to evaluate the phenolic composition and bioactivities of acorn shell samples and determine their potential as a functional compound source. In total, five acorn shell samples collected in different locations and from different species were analyzed: Q. rotundifolia ( Q. rot-1 and Q. rot-2 ), Q. suber ( Q. sub-1 and Q. sub-2 ) and Q. robur ( Q. rob-1 ). A total of nine phenolic compounds were tentatively identified, namely gallic and ellagic acids and derivatives. Digalloyl hexoside was the compound detected in higher concentrations in all extracts (2.093 – 8.3 mg/g extract). Q. suber samples exhibited the lowest IC 50 values for TBARS assay, lower than the positive control used (Trolox). Overall, the studied samples demonstrated the capacity to inhibit the proliferation of all tumor cell lines tested. Sample Q. sub-1 demonstrated the most promising antibacterial capacity. According to the results, the acorn shell extracts exhibited promising potential, and it may be interesting to conduct a deeper study on the samples of this species. • Acorn shell extracts are a sustainable source of valuable bioactive compounds. • Nine polyphenols were tentatively identified, namely gallic and ellagic acids. • Some extracts showed higher antioxidant activity, exceeding commercial control. • Extracts inhibited tumor cell proliferation and exhibited antimicrobial properties. • Potential applications include functional foods, nutraceuticals, and preservatives.