Ultrasound-assisted alkaline treatment promoted covalent complexation of soy protein isolate with ferulic acid into coating formation for guava preservation.

Soy protein isolate (SPI) -ferulic acid (FA) covalent complexes were prepared using an ultrasonic-assisted alkaline treatment method and applied in food packaging. The results showed that assisted treatment reduced the average particle size of the SPI-FA composite (from 175.94 ± 7.24 nm to 66.78 ± 1.81 nm), and the particle size distribution became more concentrated. Ultrasonic-assisted treatment increased the polyphenol grafting degree by 15%. FTIR spectroscopy analysis showed that FA was bound to SPI via covalent bonds. Evaluation of the film's performance showed that the introduction of the composite significantly enhanced its water resistance, barrier properties, and antioxidant performance. In guava storage experiments, the composite coating effectively maintained fruit appearance quality and significantly delayed weight loss, titratable acid, and ascorbic acid loss. Therefore, ultrasonic-assisted alkaline treatment may be a promising method for preparing protein-polyphenol covalent composites, offering new options for food-grade active packaging.