Characteristics of Zein-Dextran Conjugates Prepared by Ultrasound-Assisted Maillard Reaction

Zein , the main storage protein of corn, exhibits limited applications in the food industry due to its poor solubility. To enhance the solubility of zein and improve its functional properties, ultrasound-assisted Maillard reaction was performed to prepare zein-dextran (Dex) conjugates with zein and Dex as substrates in this study. The Maillard reaction conditions were optimized using response surface test based on single factor experiments. The effect of ultrasonic time on the structural and functional properties of Maillard reaction products was also investigated. The results showed that the optimal conditions for ultrasound-assisted Maillard reaction were as follows: ultrasonic power 250 W, ultrasonic temperature 65 ℃, ratio of sugar to protein 2:1 (w/w), protein concentration 2% (w/v), ultrasonic time 2 h, and degree of glycosylation 23.33%±0.58%. With an increase of ultrasonic time, the accumulation of intermediate products and the degree of browning significantly increased (P<0.05) and the blue shift of absorption peaks in the amide I, II, and III regions in Fourier-transform infrared spectra confirmed the successful preparation of zein-Dex conjugates. Scanning electron microscopy revealed the microstructure of zein before and after the Maillard reaction transformed from an initially smooth and flat surface to a honeycomb-like porous structure. The Maillard reaction induced the fluorescence quenching in both intrinsic and synchronous fluorescence spectra of zein and the increased intensity of characteristic absorption peaks of its ultraviolet absorption spectra. The results indicated that the Maillard reaction changed the molecular conformation of zein. At 2 hours of ultrasonic heating treatment, the solubility, emulsifying activity, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging rate were increased by 4.89-fold, 5.17-fold, and 3.17-fold, respectively (P<0.05). The reducing power was enhanced by 23% (P<0.05) and the foaming capacity was also improved to a certain extent (P<0.05). This study confirms that ultrasound-assisted Maillard reaction can effectively improve the solubility and functional properties of zein and provide a theoretical basis for its application in the food industry.