Effects of different treatments on the phenolic composition of acorn extracts from Quercus robur and Quercus rotundifolia
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The European oak (Quercus robur L.) and the holm oak (Quercus rotundifolia Lam.) are two examples
of endemic species that already contribute for the socio-economic development of the Iberian
Peninsula. The first one stands out because of its wood, and the second one has been traditionally
managed as savannah-like ecosystems for livestock breeding [1]. However, from a chemical
perspective, the potential of these plants, especially their acorns, can be further expanded.
For this work, acorn samples of the two mentioned species were submitted to four different extraction
methods in order to characterize the phenolic compounds of each extract. The four extractions were
the following: 1 – maceration with water at 40 ºC for one hour; 2 – infusion with boiling water for 5
minutes; 3 – decoction with boiling water for 5 minutes; 4 – maceration with ethanol 80% (v/v) at
room temperature for 1 hour. The extractions were performed using a solid/liquid ratio of 25 g/L and
the phenolic compounds were analyzed by HPLD-DAD-ESI/MS [2].
The average extraction yields ranged between 9.58 – 21.89 g of extract/100 g for Q. robur and from
2.88 to 6.82 g of extract/100 g for Q. rotundifolia. Regarding the composition of phenolic compounds,
gallic and ellagic acids were the most abundant molecules found in the samples of these species [3].
The total content of phenolic compounds varied between 71 - 124 mg/g of extract and 70 – 90.5 mg/g
of extract in Q. rotundifolia and Q. robur, respectively. Gallic acid was the compound which was found
in the greatest concentration in all the extractions, reaching its maximum concentration when the
aqueous maceration extraction was applied. Ellagic acid and its derivatives (ellagitannins) were also
found in the extracts, but to a lesser extent than gallic acid.
Considering the extraction yield and the content of phenolic compounds, the most promising
extraction method was the aqueous maceration, which could be applied to obtain extracts rich in gallic
acid and ellagitannins from acorns.
