- 學苑 = GAKUEN (ISSN:13480103)
- vol.902, pp.34-45, 2015-12-01
Pidan is a type of food produced by coagulation through alkaline denaturation, of the protein contained in eggs. Pidan is prepared according to traditional methods that are often unclear. Lead monoxide and copper sulfate are often used, as they were purported to promote coagulation of the egg. The current Food Sanitation Act in Japan forbids the use of chemicals that include heavy metals such as lead monoxide in the pidan preparation process. The lead content standard for pidan imported from China is 0.5 mg or less per 1 kg. In 2013, however, problems arose in China with pidan made using copper sulfate. For food safety reasons, it is desirable to make and distribute pidan within Japan. In this study, we located methods of preparing pidan in the literature, summarized them, and compared the methods. A literature search on methods of pidan preparation revealed 13 studies on coating methods, 11 on immersion methods, and 6 on mixed methods. Examination of these methods revealed that the materials used as the alkaline agent in the coating method were sodium carbonate, lime(including quicklime and lime hydrate), and plant ash. Salt was added to all coating agents. Some methods used black tea. In the immersion method, highly alkaline sodium hydroxide and sodium carbonate were used as well as quicklime. Few used plant ash. Some methods added black tea leaves. In the mixed method, highly alkaline chemicals were used to coagulate the egg, similar to the immersion method, and the egg was then coated with an alkaline agent and allowed to age. We then selected one method each from among the coating and immersion methods discussed in the literature and used them to prepare pidan using chicken and quail eggs. The immersion method was easier and had a higher success rate than the coating method. In particular, immersing quail eggs for 10 days and then coating them in paraffin for 52 days sometimes resulted in "Shokatan" eggs, which have white pine needle-shaped crystals on the egg white.