Effect of hsian-tsao gum (HG) content upon rheological properties of film-forming solutions (FFS) and physical properties of soy protein/hsian-tsao gum films

• HG content significantly affected the viscoelastic properties of FFS.
• Blending HG with SPI film could improve physical properties of SPI film.
• NMR revealed the addition of HG significantly changed the water state of SPI films.
• The interactions between SPI and HG were demonstrated by ATR-FTIR spectroscopy.

The effect of hsian-tsao gum (HG) content upon both rheological properties of soy protein/hsian-tsao gum film-forming solutions (FFS) and physical properties of films was studied. It was verified that the HG content significantly affected the viscoelastic properties of FFS. Lower HG content (≤30%) decreased apparent viscosity, elastic modulus (G′) and viscous modulus (G″) of FFS. However, blending of higher HG content (>30%) showed a reverse trend. Moreover, the results indicated that the addition of lower content (≤30%) HG to the soy protein isolate (SPI) films provided blend films with better mechanical properties, less sensitive to moisture and stronger barrier properties against water than pure SPI film. The analysis of nuclear magnetic resonance (NMR) revealed the addition of HG significantly changed the water state of SPI films. In particular, the free water ratio of blend films compared with pure SPI films significantly decreased. It implied that intermolecular interaction between SPI and HG resulted in the increase of hydrophobic interaction of films. Fourier transformation infrared (FTIR) data and SEM photographs indicated Maillard reactions occurred between SPI and HG, giving rise to a more compact structure than SPI films.

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