Sensitivity of oat protein solubility to changing ionic strength and pH

Abstract: Understanding the relationship between ionic strength and protein solubility is essential to the utilization of salt in the formulation design of plant protein-based food and beverage products. In this study, suspensions of oat protein isolate (OPI) were treated with two kinds of common salts (sodium chloride NaCl; sodium phosphate NaP) at different ionic strengths (I). Electrical conductivity, protein solubility, particle size, and protein profile (sodium dodecyl sulfate–polyacrylamide gel electrophoresis) were analyzed. The results showed the highest protein solubility at extremely low I (< 0.005 for NaCl; < 0.012 for NaP) and a minimum solubility at I 0.03 to 0.2 depending on the type of salt. Particle size and electrophoretic patterns supported the solubility profile. The combination effect of ionic strength and pH was also investigated. A characteristic U-shaped solubility curve observed within pH 2.0 to 8.0 at low ionic strengths (I < 0.01) was altered by increasing the salt concentration. The findings demonstrate that ionic strength and ion species play a crucial role in oat protein solubility, and the ionic effect can be modified by changing the pH. Therefore, the application of appropriate salt concentrations is vitally important to the manufacture of oat protein-based food products. Practical Application: Sodium chloride and phosphate are two of the most widely utilized salts in food processing. This study highlights the relationship between ionic strength of the two salts and oat protein solubility at different pH levels, providing useful information for selecting proper salt concentrations in the manufacture of oat protein-based food products.