pH-Dependent Effect of Lecithin on Lupin-Protein-Based Egg Custard Mimics

ABSTRACT

This study presents lupin-protein-stabilized emulsions across pH 6.0–8.0, containing 9.92% protein and 7.97% lipid, which formed egg custard mimics upon steaming. To support emulsion stability and potential nutritional benefits, soy lecithin, a phospholipid mixture, was added at 1.0% (w/w) to the emulsion. The effect of lecithin on the gel strength of the mimics was investigated, considering its varying impact across different protein systems. The binding affinity of phosphatidylcholine for β-conglutin across pH 6.0–8.0 was consistent, ranging from −14.89 to −15.53 kcal/mol. At pH 8.0, hydrophobic interactions and hydrogen bonding among proteins were least extensive. Thus, those disrupted by phospholipid complexation were outweighed by those it promoted, both among proteins and between proteins and phospholipids. This resulted in smaller pores, reinforcing the gel strength of the mimic. In contrast, adding lecithin at pH 6.0 and 7.0 reduced hydrogen bonding, which at pH 6.0 also diminished disulfide bonding, ultimately weakening gel strength. As pH influenced protein retention through molecular interactions more strongly than lecithin, retention was highest at pH 6.0 (83.6%) and lowest at pH 8.0 (35.4%), both without lecithin. Correspondingly, these mimics were the strongest and weakest, respectively, based on dynamic consistency index (5.47 vs. 0.783 kPa sⁿ) and breaking force (9.60 vs. 3.81 g). Overall, the mimics were perceived to have gel strength, moisture release, and greasiness comparable to egg custards, though they were grittier and stickier. Besides demonstrating their potential as nutritious egg alternatives, this study offers insight into the textural implications of protein gels incorporating lecithin.

Practical Applications

This study presented plant-based egg custard mimics made from lupin-protein-stabilized emulsions, which exhibited textures similar to traditional egg custards. Adding 1.0% soy lecithin altered gel strength in a pH-dependent manner and slightly increased grittiness. These findings on how lecithin affected the texture of lupin-protein emulsion gels provide food companies with practical insights for utilizing lecithin to enhance shelf stability and nutritional benefits in plant-based products.