PULSED ELECTRIC FIELD INDUCED STRUCTURAL MODIFICATION OF SOY PROTEIN ISOLATE AS STUDIED BY FLUORESCENCE SPECTROSCOPY

Abstract

ABSTRACT The effects of electric field intensities of 22 and 25 kV/cm and pulse numbers of 30, 60, 90 and 120 on the intrinsic fluorescence intensity, the extrinsic fluorescence intensity and the surface hydrophobicity of the soy protein isolate (SPI) were measured. The pulsed electric field (PEF) treatment increased the intrinsic tryptophan fluorescence intensity of the SPI causing a 2–6 nm red shift in the emission wavelengths. The extrinsic fluorescence intensity of the SPI also increased resulting in a 2–6 nm blue shift. These results indicated that the microenvironment of the soy protein's tryptophan residues changed from a less polar to a more polar environment. Also the changes in the extrinsic fluorescence intensity indicated that the soy protein fractions were partly denatured under the PEF treatment conditions that subsequently led to increase in the surface hydrophobicity. These observations confirmed that PEF treatments modified the protein structure of the SPI and increased its surface hydrophobicity. PRACTICAL APPLICATIONS Soy protein isolate (SPI) is usually the main ingredient in most soy food products and is used to manufacture textured vegetable proteins. Pulsed electric field (PEF) treatments increased the intrinsic and extrinsic fluorescence as well as the surface hydrophobicity of the SPI. These changes and modification of the SPI are valuable and useful during the production of specific food products. For example, in the processing of liquid foods containing SPI, controlled PEF treatments could be used to modify the structure and functional properties in order to achieve the desired or specific food products. The PEF treatments could also be used either as an alternative or in combination with other processing methods to induce the required structural modifications.