RESUMO
The impact of high-intensity ultrasound (HIU, 20 kHz) on the physicochemical and functional characteristics of gourd seed protein isolate (GoSPI) was studied. GoSPI was prepared from oil-free gourd seed flour through alkaline extraction (pH 11) and subsequent isoelectric precipitation (pH 4). The crude protein concentration of GoSPI ranged from 91.56 ± 0.17 % to 95.43 ± 0.18 %. Aqueous suspensions of GoSPI (1:3.5 w/v) were ultrasonicated at powers of 200, 400, and 600 W for 15 and 30 min. Glutelins (76.18 ± 0.15 %) were the major protein fraction in GoSPI. HIU decreased the moisture, ash, ether extract, and nitrogen-free extract contents and the hue angle, available water and a* and b* color parameters of the GoSPI in some treatments. The L* color parameter increased (7.70 %) after ultrasonication. HIU reduced the bulk density (52.63 %) and particle diameter (39.45 %), as confirmed by scanning electron microscopy, indicating that ultrasonication dissociated macromolecular aggregates in GoSPI. These structural changes enhanced the oil retention capacity and foam stability by up to 62.60 and 6.84 %, respectively, while the increases in the solvability, water retention capacity, and emulsifying activity index of GoSPI were 90.10, 19.80, and 43.34 %, respectively. The gelation, foaming capacity, and stability index of the emulsion showed no improvement due to HIU. HIU altered the secondary structure of GoSPI by decreasing the content of α-helices (49.66 %) and increasing the content of ß-sheets (52.00 %) and ß-turns (65.00 %). The electrophoretic profile of the GoSPI was not changed by HIU. The ultrasonicated GoSPI had greater functional attributes than those of the control GoSPI and could therefore be used as a functional food component.
RESUMO
The objective of this study was to investigate the impacts of high-intensity ultrasound treatments on the compositional, physicochemical, biochemical, functional and structural properties of canola protein isolates (CPI). Aqueous canola protein suspensions were sonicated at 40â¯kHz for 15â¯min and 30â¯min. The moisture content, water activity, bulk density and the L* and a* color parameters of the CPI decreased due to the ultrasound; however, the in vitro protein digestibility was not modified by the treatment. Glutelin (57.18%) was the main protein fraction in the canola protein isolate. SDS-PAGE demonstrated that there were no changes in the protein electrophoretic patterns, thus indicating that sonication did not break the covalent bonds. However, the ultrasound treatment improved the protein solubility, oil absorption capacity and the emulsifying, gelation and foaming properties, but these improvements depended on the pH and ultrasound exposure time. Scanning electron microscopy revealed that the ultrasound treatment disrupted the microstructure of the CPI by exhibiting larger aggregates as a lyophilized powder. In addition, there was an increase in the surface hydrophobicity and a decrease in the size of the particles of the canola protein due to the ultrasound effects, which indicates a destruction of the particles or a dissociation of the protein aggregates in the canola protein dispersions. These results suggest that ultrasound treatment is a valuable tool for improving the characteristics of canola proteins for use in foods.
