| Sunflower protein is a potential protein resource for its nutritional value and economic costs. However, its processing and utilization was limited for the poor water solubility. In this study, enzymatic modification technology was applied to improve the functional properties of sunflower protein isolate(SPI) with biochemical and spectroscopic methods, the effect of enzymatic modification on structure and functional properties of SPI was explored from the perspective of conformation and solution properties. So, a further study on this project would be helpful for the optimization of product processing and the proper application of SPI.In the present work, SPI was hydrolyzed by Alcalase, to investigate the influences of different degrees of hydrolysis(DH) on structural characteristics and functional properties. Protein hydrolyzates of different DH were obtained. The structural characteristics of modified SPI were characterized by amino acid analysis, micorstructure analysis, size exclusion chromatography, particle size, molecular flexibility and fluorescence spectrometric analysis, contents of sulfhydryl and disulfide bonds, surface hydrophobicity and differential scanning calorimetry(DSC). And the functional characteristics of modified SPI were characterized by solubility, foaming properties, emulsifying properties, oil binding capacity, apparent viscosity, turbidity and in vitro digestibility, at the same time, original proteins was used as control.The structural characteristics of SPI was modified induced the enzymatic modification. Results revealed that hydrolyzates with different DH had desirable essential amino acid profiles and showed the similar amino acid compositions.Scanning electron microscopy(SEM) revealed that the the network structure of SPI was modified, the sheet-like structure was the peptides with different molecular weight distribution. CD analysis results showed that the modified SPI possessed less α-helix and β-sheet, exhibiting instead an open random-coil structure. More random coil structure provided more flexible protein structural units for SPI. Molecular weight distribution and particle size distribution revealed that the peptide pond broke after the SPI was hydrolyzed, the particle size was decreased gradually. Fluorescence spectrometric analysis revealed that fluorescence spectroscopy maximum absorption wavelength had bathochromic shift and fluorescence intensity was significantly reduced. The bathochromic shift indicated that hydrolyzates had a flexible tertiary conformation. The reactive sulfhydryl content and the disulfide bonds were decreased, the hydrophobic surface also appeared the same change trend, denaturation temperature(Td) showed an overall increasing trend and enthalpy chage of denaturation(ΔH) was significantly reduced. The results revealed that disulfide and hydrogen bonds broke and the extent of the ordered structure was decreased.Resulting from the influence on structural characteristics, a diverse effect of enzymatic hydrolysis on the functional properties was observed. Compared with native sunflower protein isolate, the solubility was significantly increased at the isoelectric point of pH 5.0(8.49 % vs. 96.78 %). The emulsifying capacity and foaming capacity of hydrolyzates with DH of 10 % was increased by 16.76 % and 2.6 folds, respectively. However, the emulsifying stability, foaming stability and oil binding capacity decreased by 59.52 %, 65.27 % and 16.67 %, respectively. Apparent viscosity of the dispersion was significantly decreased and behaved shear thinning behavior during shear treatment. Turbidity were decreased at different pH values, especially near the isoelectric point, the aggregation was more obvious. During pepsin hydrolysis and pepsin-trypsin hydrolysis process, in vitro digestibility of hydrolyzates with DH of 30 % was increased by 3.4 folds and 50 %, respectively... |
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