Switchable pH-responsive Biopolymeric Stabilizers Made by Sonothermal Glycation of Sodium Caseinate with κappa-carrageenan

Abstract

Food-approved biopolymeric stabilizers that can construct stable emulsions, but destabilize on purpose using a specific stimulus like pH change would be of great importance to food and pharmaceutical industries (bioactive delivery). However, such edible stabilizers are reasonably rare, since they must possess superb interfacial activity (rapid, robust, and reversible adsorption at the oil/water interface) to be efficient in the stabilization of such unique systems. Herein, we report the formation of sodium caseinate (SC)-κappa-carrageenan (kC) conjugates that can offer such stabilizing ability. SC-kC conjugates were prepared by wet-heating Maillard reaction after sonication pre-treatments (400 W, 20 kHz) for 10, 20, and 30 min. The SC-kC conjugation was confirmed by Fourier transform infrared spectroscopy, CD spectra, and glycation degree (GD). With increased sonication duration, a higher GD (59.75 ± 0.69% in 30 min) was observed, which led to an improved interfacial activity (higher adsorption quantity and rate at interface), lower particle size (< 500 nm) as well as higher emulsifying activity and stability indices. It was observed that the emulsion prepared with the 30 min ultrasonic conjugate had the lowest mean droplet size (1.65 ± 0.10 μm) and polydispersity index (0.46 ± 0.00) along with the highest absolute zeta potential value (-35.76 ± 0.54 mV). Furthermore, it was found that sonothermal glycation with kC empowered the SC to fabricate emulsions with excellent pH-responsive behaviors where it can be easily switched on (pH = 7) and off (pH = 4.5) over four cycles and remain stable with further emulsification. Therefore, unique emulsion systems with attributes desired for many applications can be fabricated by SC-kC conjugates.