Gall-nuts of native oak species as a potential tannin raw material

Oak gall-nuts are pathological excrescences on the leaves of oaks (in Poland: Quercus robur L. and Q. petraea Liebl.) created by the Cynips quercusfolii L. The potential medical use of these non-wood forest products should be taken under consideration because of widespread use in folk medicine, but also because of the presence of gall-nuts of Middle Eastern oak species Quercus infectoria in the current Farmakopea... [2017]. The aim of this study was the preliminary analyzes of Quercus robur L. galls in the context of the diversity of the raw material and its possible consequences for the variability in tannin content, and therefore for the therapeutic value. The galls were collected in September 2018 from five living trees forming compact mid-field tree plantation in Podkar-packie Region (SE Poland). To determine the tannin content, hide powder method was used, while mass spectrometry was used for determining the identity of the raw material. The tannin content was found to be between 10.02 +/- 0.2% and 15.47 +/- 0.07%. There were no statistical differences between the tannin content of four weight groups of tested gall-nuts. The analysis of mass spectra showed the presence of gallic acid and tannin disintegration products. The results indicate that the tannin content in domestic oak galls is lower than in Quercus infectoria ones, for which less than 20% is required, however Polish galls are still the richest native tannin raw material. It was not proved that the content of tannins in oak galls was influenced by their size. A large variation in tannin content depending on the sample suggests that it might be possible to identify i.e. forest sites or climatic zones, where the obtained gall-nuts will be characterized by the high tannin content.