Unraveling the effect of dehulling methods on the nutritional composition of acorn quercus spp.

The nutritional composition of different acorn species (Q. pyrenaica, Q. robur, and Q. ilex) harvested in Peneda-Gerês Park, Braga (north of Portugal) was determined after being dehulled by different methods (manually, thermally by scalding with boiling water, and drying at 30 °C). Ash and protein contents remained unaltered, but the fat and carbohydrate contents increased and/or decreased depending on the dehulling method and Quercus spp. The thermal dehulling and dehulling by drying significantly increased the total fiber contents between 37-87% and 31-50%, whereas the energy values decreased between 3-10% and 3-7%, respectively. Resistant starch content decreased between 42-76% and 26-35% after thermal dehulling and dehulling by drying, respectively. The lipidic and amino acid profiles also remained unaltered after both dehulling methods, but elements and soluble sugars contents increased and/or decreased depending on the dehulling method and Quercus spp. The harvested dried acorns had significantly lower energy, fat, and fatty acid contents, but a higher carbohydrate content (more total fiber and resistant starch, and fewer sugars) when compared to commercial acorns (Q. suber and Q. ilex blend) from Alentejo (south of Portugal). Protein, amino acid, and ash contents were similar, but the harvested acorns had more potassium than the commercial ones.