Gelling, microstructure and water-holding properties of alpha-lactalbumin emulsion gel: Impact of combined ultrasound pretreatment and laccase cross-linking

The gel strength, microstructure and water-holding capacities (WHC) of emulsion gels, modified by combined ultrasound (US, 20 kHz, 600 W) pretreatment (0, 20 and 40 min) and laccase cross-linking treatment of α-lactalbumin (α-LA)-stabilized emulsions (at protein concentration 12%, w/v; oil volume fraction, 10%, w/v), were studied and compared. Significant differences in gel strength, WHC, and morphological changes have scrutinized among various emulsion gels prepared with laccase cross-linking US-α-LA (α-LA treated with US pretreatment) and US-α-LA. The gel strength of laccase cross-linking US-α-LA and US-α-LA significantly increased from 201.4 to 274.1 g and 22.8–49.4 g, respectively, with US duration ranged from 0 to 20 min. Furthermore, gel WHC of laccase cross-linking US-α-LA and US-α-LA also remarkably increased from 91.1 to 95.9 and 61.7–70.8%, respectively. The laccase cross-linking US-α-LA and US-α-LA had more uniform and denser microstructure than control. Moreover, the emulsion with laccase cross-linking US-α-LA gave a self-standing elastic gel, which showed stability for more than one month without showing any separation. In conclusion, the most appropriate combined processing technique to make a stable gel was the moderate US duration (20 min). It had a remarkable impact on physicochemical and microstructural attributes of emulsion gel, producing better substrates for laccase. Our obtained results suggested that for functionality modification of the globular protein, ultrasound pretreatment combined with laccase is an effective method.