Foam properties and interfacial behavior of the heteroprotein complex of type-A gelatin/sodium caseinate

Abstract

Foam is one special colloid dispersion system and has been widely used in foods. This work aims to improve the foam properties of sodium caseinate (Cas) through the electrostatic complexation of Cas and type-A gelatin (GE), in which GE is one cheap and widely sourced basic protein. Turbidity and zeta potential measurements indicate that mass ratio (r = GE/Cas) was critical to the solubility of protein complexes at pH 6.0 and that soluble and insoluble complexes were respectively formed at low mass ratios (r = 0.25, 0.5 and 1) and high mass ratios (r = 2 and 4). All soluble and insoluble complexes exhibited better foaming capacity than that of Cas and GE, while only soluble complexes significantly improved the foam stability of Cas. Particularly, the foam half-time of GE/Cas mixture at r = 0.25 was 5525.2 ± 405.7 s and 2.1 times that of Cas. Surface dilatational rheology shows that the adsorption behavior of soluble and insoluble complexes was respectively similar to that of Cas and GE. Soluble complexes formed more viscoelastic interface films than Cas, which could explain the better foam stability of soluble complexes. Transmission electron microscopy shows that electrostatic complexation of GE/Cas destroyed the micelle structure of Cas to varying degree but produced new networks. GE/Cas heteroprotein complexes have the potential to be used as excellent foaming agents in food industry.