How do sushi restaurants keep avocados from turning brown?
Soak in Water
The water bath method prevents the sliced avocado from oxygen exposure. Place the avocado slices in a bowl filled with cold water. Keeping avocados submerged in water for not more than 4 hours will keep the avocado from turning brown. This is the method most chefs use when preparing avocados in advance.
Do Japanese put avocado in sushi?
It is not an ingredient used in traditional sushi, but there are places that serve this type of sushi in Japan. It is not a part of Japanese traditional sushi (and avocado is not a native fruit in japan).