Protein Denaturation, Rheology, and Gelation Characteristics of Radio-Frequency Heated Egg White Dispersions

Abstract

Gel properties of radio frequency (RF) heated egg white dispersions at 27.12 MHz were studied as function of concentration (2.5–2.5 kg/100 kg sample), pH (3–11) and heating time (60–180 s). Egg white dispersions demonstrated a gradual liquid-solid transformation as they denatured and gelled during RF treatment. The critical concentration and heating period for egg white protein denaturation and gelation were found to be 7.5% (w/w) and 150 seconds. The elastic modulus (G′) of RF-heated samples increased with concentration and heating period (temperature), whereas complex viscosity (η*) increased exponentially with concentration. In an alkaline condition, the egg white dispersion did not produce a gel; however, in acidic condition it resulted in a strong gel with significantly (P < 0.05) higher G′. This could be attributed to the high dielectric constant (ε′) and loss factor (ε″) values of acidified samples as compared to the alkaline and control egg white dispersion. Effect of heating rate (1, 5, 10, and 20°C/min) in situ on rheometer plate significantly affected gel rigidity; the RF treated sample rigidity was comparable to samples heated at the rate of 5 and 10°C/min. Differential scanning calorimetry, dielectric measurement, and sodium dodecyl sulfate (SDS) PAGE electrophoresis results were used to confirm gelation behavior during both conventional and RF heating conditions.