WIKI說是自然雜交出來的,non-browning, often sold pre-sliced

opal® is the brand name for apple cultivar 'UEB 32642'. The variety originates from a natural crossing of 'Golden Delicious' with 'Topaz'.[1]

Developed by the Institute of Experimental Botany in Prague,[2] it is grown by FirstFruits Farms LLC in Washington and marketed by FirstFruits Marketing.[3][4]

It is also cultivated in Austria, Italy, Spain, Germany, Slovenia, France[5] and the United Kingdom. 'UEB 32642' is a variety registered at the Community Plant Variety Office of the European Union[6] under EU N°: 16749.

This variety of apple is naturally low in polyphenol oxidase and is often sold pre-sliced.

https://en.wikipedia.org/wiki/Opal_(apple)