Stability of native/thermally denatured myofibrillar protein particles: Improvement with decreasing pH

The physicochemical properties of myofibrillar proteins in their native and denatured states can be modulated to allow limited protein stabilization through rational acid treatment. Herein, the effects of varying pH values (2.5–4.5) on the stability of native and thermally induced myofibrillar proteins (MPs and TMPs, respectively) particles were studied via the addition of citric acid (CA) solutions. After heating at 80 °C, the α-helix content of the MPs particles without CA decreased from 43.40 ± 1.36 to 29.80 ± 1.15%. At identical environmental pH, the TMPs particles formed by heating had difficulty forming aggregates, and their size of without CA (10 μm) was smaller than that of the MPs particles (1 mm). Optical microscopy results revealed that the dispersion of the TMPs particles was improved upon CA addition, unlike that of the MP particles. However, the carbonyl content of MPs particles is lower than that of TMPs particles, and the total sulfhydryl content is higher than that of TMPs particles. In addition, as the pH of TMPs particles is adjusted to 2.5, protein content increased from 9.28 ± 1.05 to 82.37 ± 1.37 mg/mL, and optical microscopy images showed that the TMPs particles at pH 2.5 were more dispersed than those at other pH values tested herein. Therefore, the TMPs particles at pH 2.5 exhibited high stability in aqueous phase.