Rheological and structural properties of protein isolates extracted from dephenolized sunflower meal: Effect of high intensity ultrasound

Abstract

In the present study, sunflower protein isolates were treated with high intensity ultrasound (HIUS) and evaluated for rheological and structural properties. Protein dispersions (10%) were given treatment with bath ultrasound (40 kHz) and probe ultrasound (20 kHz) for 5, 10, 20 and 30 min. Probe ultrasound treatment showed higher effect on the rheological and structural changes in protein isolates as compared to bath ultrasound treatment due to higher intensity. The effect of ultrasound on rheological properties was examined by monitoring the changes in storage modulus (G′), loss modulus (G″) and loss tangent. Storage modulus and loss modulus increased, while loss tangent decreased, indicating the formation of stronger gel after ultrasound treatment. Change in tertiary and secondary structure was observed by intrinsic fluorescence and circular dichroism, respectively. The conformation of protein was altered with decrease in α-helical content and concomitant increase in β-sheet content. Ultra-sonication changed the surface morphology considerably with more heterogeneous and disordered surfaces and showed the formation of clumps with different sizes and shapes. The regular confirmation of proteins was altered along with reduction in crystalinity in HIUS treated samples as measured by X-ray diffraction. Ultrasound treatment increased the thermal degradation of protein isolates as determined by thermal gravimetric analysis. The structural changes in protein isolates altered their behaviour, which resulted in better functional properties and thereby increased the application in different food systems.