Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 2006
Publication Date: January 20, 2007
Citation: Mohamed, A., Hojilla-Evangelista, M.P., Peterson, S.C., Biresaw, G. 2007. Barley protein isolate: thermal, functional, rheological and surface properties. Journal of the American Oil Chemists' Society. 84(3):281-288. Interpretive Summary: The main objective of this work was to develop new uses for alternate crops. Barley is the fourth most used cereal world wide. Barley contains 11-16 percent protein and is mostly used in brewing and feed. A comprehensive product development for the food industry is needed using barley proteins to attract investors. To complement agronomist effort, the protein group of the Cereal Products and Food Science Unit of the NCAUR participated by developing procedures to characterize and compare barley proteins to more popular cereals. This project was focused on determining thermal and rheological properties of barley protein isolates. Utilization of barley proteins in baked and pasta products can also be considered to increase the nutritional value of these products. The use of barley in the snack industry can be explored by developing different extruded snacks with high protein content. Barley protein's structure-function was also explored to increase chances for use in different types of foods (i.e., foaming properties, gel strength, heat stability) and interactions with other food components. Basic physical, mechanical and rheological properties and performances of barley proteins and oils were performed to provide information and direction for end-use food and non-food applications.
Technical Abstract: Barley protein isolate (BPI) was prepared using hexane-defatted commercial barley flour. BPI was extracted in 0.05 N NaOH in a 10:1 ratio solvent:flour. The BPI was precipitated by adjusting the pH to 4.5 and freeze-dried. The thermal properties of the BPI were determined by Modulated Differential Scanning Calorimetry (MDSC). The onset or peak temperatures, and delta Cp were recorded. BPI exhibited a glass transition (Tg) with 140 deg C onset, 153 deg C middle, or 165 deg C end temperatures and a delta Cp of 0.454 J/g deg C. The high moisture content sample showed a Tg at 89 deg C, 91 deg C, or 94 deg C and 0.067 delta Cp. Acetylation had no apparent effect on 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 percent 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 BPI, unmodified and modified, possesses surface activity. BPI was the most effective in lowering the surface tension of aqueous NaCl, while the crosslinked BPI was the least effective. To determine the linear viscoelastic range of the suspension, G' was observed as a function of strain. The magnitude of G' 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 3-10 percent.