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Comparison of nutritional and bioactive properties of acorn flour with and without tannins

Publication . Ben Rhouma, Hiba; Carocho, Márcio; Barros, Lillian

The Quercus spp. are a varied group of evergreen and deciduous trees native to temperate and tropical regions. There are about 600 species of Quercus worldwide, which differ in their flowering and fruiting dynamics as well as maturity index. Acorns, the nuts of Quercus spp. trees, offer a comprehensive nutritional profile, being rich in proteins, fibers, starch, bioactive compounds including tannins and phenolic acids, essential vitamins, like vitamins A and E, and minerals, such as potassium, iron, calcium, and magnesium. However, this fruit presents a problem for the food industry regarding the astringency caused by tannins, which are anti-nutrients found in acorns. Therefore, this study aims to evaluate the potential of acorn flour for the baking industry by comparing the nutritional value and bioactive compounds of acorn flour with and without tannins. The whole flour (SPM21) and a tannin-free flour (SPM21F4) were analysed, having both been supplied by the company Landratech. The elimination of tannins, which was accomplished by leaching the flour three times with water at 15 °C, resulted in a reduction in several nutrients, such as crude protein, ash, and fiber. However, the SPM21F4 flour showed increased levels of moisture, crude fat, starch, total carbohydrates, and energy content. Soluble sugars were found exclusively in the SPM21 flour, indicating that the leaching treatment affected the sugar content in the SPM21F4 sample. The fatty acid profile of the SPM21F4 flour revealed higher levels of polyunsaturated fatty acid (PUFA) and monounsaturated fatty acid (MUFA), while the flour containing tannins had higher levels of saturated fatty acids (SFA). Ten phenolic compounds were detected, and the tannin free flour had a much lower overall phenolic content. In conclusion, properly processed acorn flour can improve the nutritional profile of bread by providing bioactive chemicals and appealing sensory features, hence increasing its popularity in the baking business. However, further research is needed to optimize tannin extraction and fully understand the nutritional and industrial potential of acorn flour.

2024Master thesis

Embargoed access

Exploring acorn shells: Phenolic composition and bioactive potential for sustainable valorization

Publication . Mateus, Cristiano; Alonso-Esteban, José Ignacio; Finimundy, Tiane C.; Mandim, Filipa; Oliveira, Izamara; Babo, Pedro; Ferreira, Isabel C.F.R.; Barros, Lillian

Pedunculate (Quercus robur L.), holm (Quercus rotundifolia Lam.), and cork (Quercus suber L.) oaks are abundant across the Portuguese landscape. This study aims to evaluate the phenolic composition and bioactivities of acorn shell samples and determine their potential as a functional compound source. In total, five acorn shell samples collected in different locations and from different species were analyzed: Q. rotundifolia (Q. rot-1 and Q. rot-2), Q. suber (Q. sub-1 and Q. sub-2) and Q. robur (Q. rob-1). A total of nine phenolic compounds were tentatively identified, namely gallic and ellagic acids and derivatives. Digalloyl hexoside was the compound detected in higher concentrations in all extracts (2.093 – 8.3 mg/g extract). Q. suber samples exhibited the lowest IC50 values for TBARS assay, lower than the positive control used (Trolox). Overall, the studied samples demonstrated the capacity to inhibit the proliferation of all tumor cell lines tested. Sample Q. sub-1 demonstrated the most promising antibacterial capacity. According to the results, the acorn shell extracts exhibited promising potential, and it may be interesting to conduct a deeper study on the samples of this species.

2025Journal article

Open access