Figure 1.

Images of pidan and ovalbumin gelation. (a) Photograph of lab-made pidan, a traditional method for preserving eggs in alkaline solution. This treatment results in the egg white forming a transparent gel so stable that pidan is known as “century eggs” in English. (b) Traditional rice porridge with pidan. The pidan is cooked in the rice, and the egg white gel remains intact and transparent. (c) Gels formed from ovalbumin, the major constituent of egg white, in strong base and strong acid. Ovalbumin in 0.25 M NaOH solution immediately forms a colorless, transparent gel (left vial), whereas ovalbumin in 0.25 M HCl solution gradually forms an opaque gel (right vial). The inset of part c shows an imaging target behind the ovalbumin in 0.25 M NaOH, demonstrating the gel’s high transparency.