Arginine can either suppress or promote the aggregation of egg white proteins depending on solution conditions.

Egg white proteins (EWPs) display complex aggregation behavior that varies with solution conditions such as pH. Although arginine (Arg) is commonly employed as a broad aggregation suppressor, several reports have shown that it can also promote aggregation, and the mechanism underlying this dual action remains unclear. In this study, we investigated how Arg, when added as an additive, influences the thermal aggregation of EWPs under differing solution conditions. Arg suppressed thermal aggregation at higher salt conditions but promoted it under low-salt conditions. In addition, N-acetylarginine (Ac-Arg) markedly suppressed the aggregation of 5 mg mL EWPs even in low-salt conditions. The aggregation response of EWPs was also found to depend strongly on the buffer's net charge. Collectively, these findings demonstrate that Arg acts in two ways, as both a salt and an aggregation suppressor, depending on salt level and buffer charge. Overall, this study contributes to a better understanding of the conditions under which Arg influences protein aggregation in food and pharmaceutical formulations.