Barley Protein Isolate: Thermal, Functional, Rheological, and Surface Properties

Barley protein isolate (BPI) was extracted in 0.015 N NaOH in a 10:1 ratio solvent:flour and was precipitated by adjusting the pH to 4.5 and freeze-dried. The thermal properties of BPI were determined using modulated differential scanning calorimetry (MDSC). BPI with 4% moisture content exhibited a glass transition (Tg) with 140 °C onset, 153 °C middle, and 165 °C end temperatures and a ΔCp of 0.454 J/g per °C. The high moisture content sample (50%) showed a Tg at 89, 91, or 94 °C and 0.067 ΔCp. Acetylation had no apparent effect on the foaming and emulsifying properties of protein from barley flour but exhibited the least-stable foam among BPI samples. Foaming capacities of both barley protein isolates were ∼12% less than that of acid-precipitated soy protein isolate reported in the literature. Acetylated BPI showed the highest surface hydrophobicity compared to the other samples. The surface-tension test confirmed that unmodified and modified BPI possessed surface activity. BPI phosphorous oxycloride-crosslinked was the most effective in lowering the surface tension of aqueous NaCl, while the crosslinked BPI was the least effective. The G′ value of BPI suspension was greater than G″ at all frequencies from 0.1 to 100 rad/s. The strain value at which linear behavior ceased and nonlinear behavior began ranged from 3 to 10%.

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