Abstract
The major component of acorn is starch, which may amount up to 55% of the dry weight. Lack of systematic knowledge on acorn starch greatly hinders the further development of acorns as sustainable crops. This review aims to summarize the current knowledge of the isolation, chemical composition, physicochemical properties, and uses of acorn starches and to provide future research directions. The amylose content of the acorn starches is reported to vary in the range of 20–39%. Moisture content, lipid, ash, and protein contents of the acorn starches have been reported varying from 2.20 to 15.50%, 0.23 to 2.64%, 0.01 to 1.41%, and 0.01 to 6.7%, respectively. Thermal and pasting properties that have usually been determined using differential scanning calorimeter (DSC) and rapid viscoanalyzer (RVA) are also discussed in this article. Acorn starch has great potential for various food and nonfood applications due to the unique structural and functional features.
Highlights
Quercus spp. represent an important genus of the Fagaceae family which consists of 600 species worldwide, including monoecious, deciduous, evergreen trees, and rarely shrubs [1]. ese species produce a widely known fruit, commonly identified as acorns, which are of vital importance for both humans and animals
Acorn utilization has been mainly limited to traditional uses. e underutilization of acorns in the food industry might be explained by some current consumer trends, and due to the lack of a number of chemical characterization studies sufficient enough to validate their true potential [2]. ere is the further constraint of their astringency, which, in some cases, might compromise their acceptability as food [18]
Amylose content of the acorn starches is reported to vary in the range of approx. 20–39% (Table 1). e difference in amylose contents of acorn starches could be readily attributed to the differences in acorn genetics, growing conditions of the crop, and methods of estimation [20, 36]. e complexes may hinder actual estimation of amylose content [37]. e moisture content of starch from different acorn sources has been reported in the range of 7.22–15.91 [20, 22, 23]. e moisture content is similar to air-equilibrated cereal starches (10–12%) and some roots and tubers (14–18%) [36]
Summary
Quercus spp. (oaks) represent an important genus of the Fagaceae family which consists of 600 species worldwide, including monoecious, deciduous, evergreen trees, and rarely shrubs [1]. ese species produce a widely known fruit, commonly identified as acorns, which are of vital importance for both humans and animals. One of the earliest methods of acorn starch isolation was proposed by [28] which include a treatment with 0.3% w/v sodium metabisulfite solution for steeping, nylon mesh (106 mm) for screening, and repeated toluene washing (10% toluene in 0.1 M aqueous sodium chloride) for removing protein and lipids. E precipitate was screened successively in 75 mm and 53 mm sieves and centrifuged Starch extracted using this process has been shown to have high purity and yield along with a less damaged structure. Li et al [7] described a method of isolation of starch from acorn which included steeping of acorn flour in 0.3% sodium hydroxide (1 : 5, w/w), screening of the dispersion through a mesh sieve a 0.18 mm, and purification by centrifugation. Acorn starch showed a lower percentage of amylopectin (AP) branched short chains (DP 6–12: 28.6%) and very long chain (DP > 37: 2.3%) and a higher percentage of AP branched long chains (DP 13–36: 69.1%) [24]
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