Structure and emulsifying properties of Grass pea (Lathyrus sativus) protein isolate (GPPI) were investigated as function of cold plasma treatment at two voltages (9.4 and 18.6 kVpp) and treatment times (30s and 60s). Optical emission spectroscopy was used to characterize the nature of air DBD-cold plasma. The content of carbonyl group, Di-tyrosine cross-link and free sulfhydryl, secondary and tertiary structures, SDS-PAGE, surface charge, surface hydrophobicity and solubility of GPPI were characterized. Results from the optical emission showed that the density of charged and reactive species were greatly dependent on the voltage applied and increased at the higher voltage. With increasing the treatment time and voltage, the content of carbonyl groups, disulfide bonds, Di-tyrosine cross-link and also surface charge in GPPI increased, which in turn led to a decrease in the absorption rate of protein into the water-oil interface. However, higher efficiency of etching and oxidation rate at 18.6 kVpp after 60s of treatment, increased the dissociation of globulins, and thus the absorption rate of protein into interface increased. Plasma treatment resulted in the formation of more orderly secondary structures such as α and β structures. The loss of tertiary structure in the treated GPPIs at 9.4 kVpp increased the ability of GPPI in lowering the interfacial tension at oil-water interface. Whereas, more compact tertiary structure, higher ordered secondary structure and dissociation of globulins in the treated GPPI at 18.6 kVpp for 60s led to the formation of an interfacial layer with higher interfacial tension value. Compared to native GPPI, oil-droplets size of stabilized-emulsions with treated GPPI at 9.4 kVpp were bigger, indicating that these proteins were not able to form a strong interfacial film around the oil-droplets and prevent them from flocculation within the homogenizer. Whereas, in the emulsion stabilized with treated GPPIs at 18.6 kVpp for 60, the superior protein absorption and formation of dens and elastic interfacial film around oil droplets led to the formation of uniform small droplets with good stability against creaming. Overall, our results indicated that cold plasma treatment had positive effect on the interfacial and emulsifying properties of GPPI in terms of thermodynamic stability of protein on interface, globulin dissociation, and increase in oil-droplet surface electrical charge.

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