Tannin content in acorns (Quercus spp.) from Poland

Abstract

Oak acorns used to be an important human food, up until recent times. The major factor inhibiting their use in modern nutrition is their high tannin content. Polish oak trees were screened in order to find out whether there are any major geographical or interspecific differences in tannin and total phenolic contents in acorns, which might help us to establish further directions in the search for low-tannin individuals. We studied the level of phenolic compounds using the standard Polish and European Pharmacopoeia method, with Folin-Ciocalteu reagent and hide powder. Altogether 49 acorn samples of Quercus robur, 13 of Q. petraea, 1 of Q. pubescens (all native) and 12 of Q. rubra (introduced) were collected in different regions of Poland. The amount of investigated phenolics in Q. robur and Q. petraea acorns was similar, and tannins constituted the main component. The Q. pubescens sample was distinguished by the lowest tannin and total phenolic content and a relatively high amount of non-tannin phenolics. Q. rubra had a slightly lower tannin content than Q. robur and Q. petraea acorns, but the level of other phenolics was much higher. The results for Q. robur suggest geographical variability of phenolic content as well as a relationship between the phytochemical and biometric parameters of oak acorns.

Acorn flour properties depending on the production method and laboratory baking test results: A review

“…Acorns are characterized by a high content tannins, which cause the bitter taste of flour obtained from this raw material (Łuczaj et al., 2014). To reduce the bitterness of the final product, additional production steps leading to eluting of tannins are necessary.…”

“…Tannins cause the bitter taste of the acorns and demonstrate anti‐nutritional properties in higher concentrations. The consequence of an excessively high tannin intake may be damage to the intestinal epithelium, liver, and kidney tissues (Łuczaj et al., 2014; Pignone & Laghetti, 2010). Tannins in acorn flour may also be responsible for its low digestibility.…”

“…A problem that may limit the consumption of acorns is the high content of tannins (Bainbridge, 1987; Łuczaj, Adamczak, & Duda, 2014). These are compounds belonging to the group of polyphenols that cause product bitterness and demonstrate an ability to form complex proteins, polysaccharides, and metal ions, thereby reducing product digestibility and absorption.…”

Biological Flora of the British Isles:Quercus rubra

“…In its native range, acorns of Q. rubra also have high tannin content—3.72% of dry mass (Basden & Dalvi, 1987). In its introduced range (in Poland), tannin contents of Q. rubra acorns ranged from 2.10% to 4.26%, with an average of 2.97% (Łuczaj, Adamczak, & Duda, 2014). Wood and bark of Q. rubra contain 1.8%–2.5% and 4.6%–11.1% of tannins respectively (Rowe & Conner, 1979; Seikel, Hostettler, & Niemann, 1971).…”

Therapeutic, Phytochemistry, and Pharmacology of Acorns (Quercus Nuts): A Review

“…The role of acorns among these wild plants has most probably been underestimated. According to Łuczaj et al [11], acorns were also consumed as emergency food in war times. Acorn kernels especially roasted ones were also used in traditional medicine throughout Europe.…”