Oak Quercus rubra L. and Quercus robur L. acorns as an unconventional source of gamma- and beta-tocopherol

Abstract

The oaks Quercus robur L. and Quercus rubra L. are grown worldwide. The oak fruits (acorns) fallen on the ground during the autumn are usually considered as unusable, although some possible applications have been reported. In the present study, the possible recovery of tocopherols from acorns of two oak species Q. rubra (n = 14) and Q. robur (n = 15) was evaluated. Four tocopherols (Ts) (α-T, β-T, γ-T, and δ-T) in the oak fruits of Q. rubra and Q. robur were identified. The Q. robur acorns had abundant γ-T (28.18 ± 6.7 mg/100 g dw), while in Q. rubra β-T was predominant (17.28 ± 2.91 mg/100 g dw), nearly 95 and 90% of total detected tocopherols, respectively. The variability of tocopherol levels within the same species was lower for Q. rubra (16.5%) and higher for Q. robur (23.4%). The principal component analysis, applied to four tocopherol homologues, confirmed their feasibility to distinguish two strictly separated groups: one for species Q. rubra and the other for Q. robur. The predominance of β-T in Q. rubra acorns is a unique finding in the plant world; therefore, acorns of this oak species can be used as an unconventional natural source of this rare tocopherol homologue.