Polypeptide-containing polysaccharides such as gum arabic are emulsifiers but have the limited polypeptide content (typically &lt;10%). Although Maillard-type conjugates with a relatively high content of proteins have shown the improved emulsifying properties, Maillard reaction is time-consuming and produces numerous undesirable byproducts, even after the conjugation. In our work, covalent casein-alginate conjugates were synthesized by the transacylation reaction, and the purified conjugates had exceptional properties emulsifying and stabilizing corn oil. Conjugation was done by mixing 1% w/v propylene glycol alginate (PGA) and different amounts of sodium caseinate (NaCas) for 2 h at pH 11.0. After dialysis to remove free molecules, NaCas-alginate conjugates with 52.8%, 66.2%, and 76.5% NaCas were prepared at NaCas:PGA mass ratios of 1:2, 1:1, and 2:1, respectively. The purified conjugates were capable of emulsifying corn oil at a low surfactant-to-oil ratio (SOR) of 0.75:100 (w:v), and the emulsions were stable at a wide range of pH and ionic strength, as well as after thermal pasteurization. A higher content of NaCas in the conjugate resulted in smaller oil droplets, whereas the alginate content was critical to the stability of oil droplets through electrostatic and steric mechanisms. To further illustrate structure-function correlations, individual α-, β-, and κ-caseins were conjugated with alginate, corresponding to protein content of 39.17%, 37.78%, and 23.14%, respectively. Similar to the NaCas conjugates, emulsions with a low SOR of 1:100 (w:v) were stabilized by individual casein conjugates, with smaller droplets at a higher protein content of conjugates. The emulsions had much lower SORs than those utilizing Maillard-type conjugates (SOR = 1:21-1:4) and did not have the undesirable color. Since the transacylation reaction is fast, is easy to scale-up, and does not produce byproducts, the casein-alginate conjugates have the potential for use as novel emulsifiers with tunable properties.

High protein content casein-alginate conjugates produced by transacylation reaction as novel emulsifiers

ACS Spring 2022

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