I am not going to get into a debate over MSG. The characteristic flavor ("unami") of Japanese mayonnaise comes from the addition of MSG. In addition, Japanese mayonnaise is made with egg yolk only. You can get a reasonable reproduction of Japanese mayonnaise by adding about a teaspoon of soy sauce (which also contains MSG), miso, malt vinegar, Chinese black vinegar or Worcestershire sauce to regular mayonnaise. Via Nasi Lemak.