Modification of β-lactoglobulin by phenolic conjugations: Protein structural changes and physicochemical stabilities of stripped hemp oil-in-water emulsions stabilized by the conjugates

Abstract

Preventing lipid oxidation at the oil-water interface is critical for suppressing food emulsion deterioration and thus minimizing the economy loss. However, it is challenging to specifically localize the needed antioxidant species at the interface, failing in which often results in poor oxidative stability of emulsions. Here, we show that by grafting gentisic acid (GA) on β-lactoglobulin (βLG) at an optimal ratio, the βLG-GA conjugate can retain the emulsification property while improving the oxidative stability of the stripped hemp oil-in-water emulsion. Upon optimizing the conjugate production at a larger scale and a thorough characterization of the surface charge, surface hydrophobicity, and surface tension of the resultant conjugates bearing different GA grafting number (to the host βLG), a series of stripped hemp oil-in-water emulsions differing in GA abundance were prepared. The physical stability of emulsions was dependent on the structure, solubility, hydrophobicity, and GA grafting number of these conjugates. The existence of precipitants was noticed in the conjugates solutions, which impacted the size, physical and oxidative stability of the emulsions they stabilized when compared to the ones emulsified by the soluble conjugates. Remarkably, we discovered that under high GA grafting number, the antioxidant capacity of the conjugate is higher than that of the raw βLG, which suggested the potential use of the soluble conjugates with high GA grafting number as advanced emulsifier bearing good antioxidant activity. This work represents the structural basis of the functional improvement of the emulsions using protein-phenolic conjugates, which provides unique insights into the future design of multifunctional food biopolymers.