Physiochemical properties and nutritional profile of Mediterranean oak acorn

Abstract

Oaks cover a vast area of Jordanian forests, and their fruit (named acorns) have good nutritional value. In this study, we investigated the physical, chemical, and nutritional characteristics of the acorns produced by three Jordanian oak species, Quercus aegilops (QA), Quercus infectoria (QI), and Quercus calliprinus (QC). The physicochemical (acorn length, weight; cupule weight, coat weight, cotyledon weight, coat weight percent, cotyledon weight percent and acorn volume) and nutritional quality (protein, fat, fiber, ash, carbohydrate, amino acid, fatty acid and mineral compostions) of the acorns from the three oak species were determined using standard procedures. The acorn of QA showed significantly greater values compared to QC for all physical characteristics assessed while QC exhibited the lowest values; QI presented intermediate values.The chemical composition of the three species showed that fat content varied from  8.18% to 8.99% and the crude fiber and the total carbohydrate content ranged from 3.27% to 3.86% and 76.20% to 81.43%,  respectively According to obtained results, oak acorn can be considered a significant source of protein (9.54% for QC to 10.9% for QA). Oak acorn
contained 18 known amino acids (AAs); with total essential amino acids (TEAA) levels in these oak species as 2307.9, 1699.1, and 2262.8 mg/100 g dry weight, respectively. The most abundant essential amino acid found varied between species: in QA it was leucine (446 mg/100 g dry weight), in QC it was arginine (526 mg/100 g dry weight), and in QI it was phenylalanine (395 mg/100 g dry weight). The ratio of TEAA to total amino acids (TAA) was 0.90: 0.50 and 0.79 for QA, QC and QI, respectively, which indicates that QA is the best species in terms of essential amino acid (EAA) proportion. The EAA scores showed that (phenylalanine + tyrosine) and (methionine + cysteine) were the most abundant AAs in oak acorns, while lysine and leucine were the most limited. The ratio of unsaturated fatty acids to saturated fatty acids in the acorn oil ranged from 3.45:1.00 to 3.93:1.00. Therefore, oak acorn oil may be considered healthy for a human diet. The most abundant minerals in decreasing order were K, P, Ca, Cl, S, Fe, and Mn. These results demonstrate that oak acorns from Jordan have great potential to be included in human feeding.

Key words: Amino acids, Fatty acids, Nutritional value, Oak acorn, Quercus L