Brillouin Light Scattering from Thin Albumen of Chicken Egg

Abstract

Chicken eggs are rich in high-quality proteins and several kinds of trace elements, and have been a very familiar nutriment for human beings since ancient times. Chicken egg white comprises two layers, namely, thin albumen and thick albumen, both surrounding the yolk within a shell. There are two types of thin albumen known as the outer and inner thin albumens. The physical properties of both types of albumen are essentially the same. Thin albumen from chicken egg, hereafter referred to as egg white (EW), gels at a gelation temperature TG of ca. 66 C. The gelation process and the rheological properties of EW have attracted the attention of biological and biochemical scientists, food scientists, and physicists. The gelation process of EW has been studied by the ultrasound pulse technique at 3MHz in the temperature range between 10 and 95 C. The velocity of a longitudinal sound wave (LSW) exhibits a broader peak with a maximum at approximately 66 C as temperature increases through the sol–gel transition. Brillouin light scattering (BLS) measurement is another powerful and convenient technique for studying thermally excited hypersonic sound waves in the GHz frequency region. By utilizing a (3+3)-pass Fabry– Perot interferometer (FPI), we expect to observe a BLS spectrum from EW even near TG. We purchased fresh Boris Brown eggs with a red shell laid within a day at a farmers market near our university just before each measurement. About 5ml of thin albumen or distilled water was transferred into a glass tube placed in a brass cell. The cell temperature was regulated up to 82 C within an accuracy of 0:1 C and monitored by an almel– chromel thermocouple. We repeated our BLS measurement six times only during a heating run. BLS spectra were probed using the 1⁄4 488 nm excitation from an Arþ laser in a single-cavity mode with an output power of 40mW. BLS spectra were obtained using a laboratory-built (3+3)-pass FPI. Since EW gradually becomes opalescent with increasing temperature above 50 C, we employed the 180 scattering geometry, which allows us to continue our BLS measurements up to 61 C. In order to determine the LSW velocity V and the refractive index n at 488 nm, we also adopted the 90A scattering geometry at 24 C. Figure 1 shows an example of the 180 and 90A BLS spectra of EW at 24 C. We performed a numerical convolution analysis of these BLS spectra by adopting the damped harmonic oscillator (DHO) function for the elastic response function Sðq; !Þ;