Study on the Characteristics of Monolayer Water and Bound Water of Wheat Flour after Cold Plasma Treatment

To understand the cause for the increasing water absorption rate of wheat shorts after cold plasma treatment, a dynamic moisture adsorption instrument was used to measure the moisture sorption isotherms of samples treated with 120 W low-pressure strong radio frequency helium or oxygen CP for different times. The result was that the Caurie equation can fit an isotherm, and its coefficient C0 gived the density of water adsorbed by the sample. For adsorbed or desorbed samples, as the helium or oxygen CP treatment time at the same power increased, there was no difference in the density of adsorbed water, and the coefficient M0 gived the adsorbed water content of the monomolecular layer of the sample. For adsorbed or desorbed samples, as the helium CP treatment time at the same power increased, the water content of the monomolecular layer increased significantly. For samples treated with oxygen plasma, the content of the adsorbed monomolecular layer water first decreased and then increased as the treatment time increased, while the desorbed single-molecule water content showed a decreasing trend with the increased time. In order to improve the fitting of the Caurie equation, M0 was corrected to A+Bt (t was the temperature, A and B were constants). Analysis of the coefficients of the modified Caurie equation showed that as the 120 W helium CP treatment time (0~180 s) increased, the monomolecular layer of water, the number of adsorbed water molecule layers, the bound water content, and the water adsorption surface area all showed a continuous increase trend. For oxygen CP, these indicators showed an increasing trend in the first 60 s of processing, and then showed a decreasing trend if the processing time was extended. The results showed that compared with oxygen-cold plasma, high-energy helium-cold plasma improved the hydrophilicity of wheat shorts proteins and polysaccharides. As the treatment time increased, the surface area and number of layers of water adsorbed by these macromolecules and the monomolecular layer, and the bound water content steadily continued to increase.