Steady Shear Rheological Properties of Native and Hydrothermally Modified Persian Acorn (Quercus brantii Lindle.) Starches

Modification of Acorn Starch Structure and Properties by High Hydrostatic Pressure

Despite being rich in starch, over half of acorn production is undervalued. High hydrostatic pressure was used to modify the properties of Q. pyrenaica (0.1 and 460 MPa for 20 min) and Q. robur (0.1 and 333 MPa for 17.4 min) acorn starches to obtain high-valued ingredients. Pressure significantly altered the span distribution and heterogeneity of the acorn starch granules depending on the species, but their morphology was unaffected. Pressurization increased the amylose/amylopectin ratio and damaged starch contents, but the effect was more prominent in Q. pyrenaica than in Q. robur. However, the polymorphism, relative crystallinity, gelatinization temperatures, and enthalpies were preserved. The pressure effect on the starch properties depended on the property and species. The solubility, swelling power, and acorn gels' resistance towards deformation for both species decreased after pressurization. For Q. pyrenaica starch, the in vitro digestibility increased, but the pseudoplastic behavior decreased after pressurization. No differences were seen for Q. robur. Regarding the commercial starch, acorn starches had lower gelatinization temperatures and enthalpies, lower in vitro digestibility, lower resistance towards deformation, superior pseudoplastic behavior, and overall higher solubility and swelling power until 80 °C. This encourages the usage of acorn starches as a new food ingredient.

The physicochemical properties and Pickering emulsifying capacity of acorn starch

In this work, the granule characteristics, functional properties, in-vitro digestibility, antioxidant capacity, and phenolic composition of acorn starch were investigated and compared to those of potato starch and corn starch, and its Pickering emulsifying ability was also evaluated. The results showed that the acorn starch granules were spherical and oval in shape, with a smaller particle size, and the amylose content and crystallinity degree were similar to those of corn starch. However, the acorn starch was difficult to swell, with poor aqueous solubility, though it had a strong gel strength and setback viscosity. Because acorn starch contained more free and bound polyphenols, its resistant starch content after cooking and ABTS and DPPH radical scavenging activities were significantly higher than those of potato starch and corn starch. Acorn starch also exhibited outstanding particle wettability and could stabilize Pickering emulsions. The assessed emulsion showed an outstanding effect for protecting β-carotene against ultraviolet irradiation and was positively correlated with the acorn starch addition amount. The obtained results may serve as a reference for the further development of acorn starch.

Blends of Cactus Cladode Powder with Corn Starch, Milk Proteins and Gelatin: Rheological Evaluation and Application to a Soup Model

Cactus cladodes (Opuntia ficus-indica) is a valuable source of dietary fibers. In this study, peeled cladode powder was produced by air drying at 40 °C and was characterized for its color, dietary fiber content, and rheological behavior. Cladode powder aqueous suspensions of 3% w/w were prepared and the effect of protein (gelatin, sodium caseinate, and whey protein) or salts (NaCl/CaCl2) on the blend’s viscosity was investigated. Additionally, cladode powder was incorporated in a soup model, aiming at substituting corn starch. Our powder had an appealing green color, but its deterioration was fast when it was exposed to light. A shear-thinning behavior was observed in all cladode-protein mixtures, but viscosity values depended considerably on the protein type and the pH values. Notably, gelatin addition led to higher apparent viscosity of cladode powder at pH 6, suggesting interactions with cladode mucilage, but this effect was reversed at pH 4, below gelatin isoelectric point. The Ostwald-de Waele model successfully correlated viscosity-shear rates data, whereas the Casson model presented a good fit mainly in starch containing systems. Corn starch substitution by cladode powder, in the soup model, led to lower consistency coefficient values. In soups, the logarithmic mixing law was applied at different corn starch: cladode powder ratios to highlight their possible interactions. The values obtained diverged slightly downwards from the logarithmic mixing law. When purified mucilage was added—instead of cladode powder—the samples diverged slightly upwards from the logarithmic mixing law.

Physicochemical Properties of Enzymatically Modified Starches

The physicochemical properties of native, annealed and enzyme-treated chickpea (CP), corn (CS), Turkish bean (TB) and sweet potato (SPS) were investigated. Germinated sorghum extract (GSET) was used as the source of enzymes. Starches were annealed in excess water by holding the slurry at 60 °C for 60 min with or without GSET. The flow curves/rheological data were fitted to the power law, Casson and Herschel–Bulkley models. Starches exhibited shear thinning behavior and a variation in the flow behavior index (n) (0.34–0.82) as a function of the starch type. The consistency index (k) of CP and CS decreased with annealing and GSET treatment but increased for TB and SPS. Annealed and GSET-treated SPS exhibited the highest yield stress compared to the other starches, except for CP. The temperature dependency of all starches was well described by the Arrhenius model (r2 = 0.88–0.99). The activation energy (Ea) values were in the range of 660–5359 (J/mol). The TB exhibited the most Ea and SPS the least. With the exception of SPS, annealing appeared to increase the Ea of all tested starches, but the range of Ea was broader for SPS and CS. Annealed and GSET starches exhibited an increase in the gelatinization temperatures (onset and peak) and a decrease in gelatinization enthalpy (ΔH). The syneresis and water holding capacity decreased after annealing or GSET treatment.

Composition, Physicochemical Properties, and Uses of Acorn Starch

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.