Abstract: The effects of microwave and ultrasound pretreatments on the properties and structure of wheat bran protein/soybean protein composite gel induced by transglutaminase (TGase) were investigated. Meanwhile, in vitro release experiments were conducted to evaluate the controlled release of three composite gels (microwave-treated, ultrasound-treated, and untreated) loaded with riboflavin. The results showed that compared with the untreated control, both ultrasonic-modified and microwave-modified wheat bran/soybean mixed protein gel (UWSPG and MWSPG) exhibited a significant improvement in texture properties, water-holding capacity, surface hydrophobicity, and intermolecular forces (P < 0.05). The hardness, water-holding capacity, surface hydrophobicity, and hydrophobic interactions of UWSPG and MWSPG increased by 111.95% and 179.97%, 21.72% and 32.43%, 101.56% and 135.67%, 153.85% and 275.27%, respectively, and the content of free sulfhydryl groups decreased significantly (P < 0.05) compared with those of the control. Amino acid composition analysis, fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and microscopic protein mixture, which was conducive to the formation of protein gels, and microwave treatment resulted in the formation of a denser, more uniform and more stable three-dimensional network structure. compared with the unmodified composite gel, the encapsulation efficiency of riboflavin in UWSPG and MWSPG increased by 4.23% and 8.42%, and the loading capacity by 10.05% and 14.22%, respectively. When the digestion time was 300 min, the release rates of riboflavin loaded in the unmodified, ultrasonic-modified, and microwave-modified gels were (87.25 ± 1.48)%, (81.03 ± 2.56)%, and (67.34 ± 2.72)%, respectively. Therefore, the microwave-modified gel exhibited more stable controlled release of riboflavin.

Key words: wheat bran protein; soybean protein; ultrasonic; microwave; gel properties; controlled release performance