Structure, emulsifying and embedding characteristics of soy protein isolate induced by the complexation of carrageenan with different charge groups

Soy protein isolate (SPI) offers high protein, nutritional benefits, and versatile functionality but requires modification due to its environmental sensitivity and functional limitations. To expand the functional characteristics and application scope of SPI, three types of carrageenan (Car) was used to form complexes with SPI. With the addition of carrageenan, the turbidity of SPI at its isoelectric point significantly decreased, and the turbidity curve shifted toward the acidic range. Structural analysis showed that lambda-carrageenan significantly reduced the hydrophobicity of SPI from 218 to 150 when combined to SPI at a Car/SPI ratio of 1:5 (P < 0.05). Fourier transform infrared spectra revealed that the electrostatic interaction between iota-carrageenan and SPI was the strongest at a ratio of 1:5. The emulsion stabilized by kappa-Car/SPI complexes had the smallest creaming index, with a creaming index of 46.6% after 7 days of storage, which was 33.3% lower than the creaming index of the SPI emulsion (P < 0.05). The iota-Car/SPI complexes exhibited the highest encapsulation efficiency for curcumin, with a value of 80.1%, which was 25.3% higher than the SPI (P < 0.05). This study could provide solutions for the modification of SPI and enhance its application in the food industry.