system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do fruits like pinneapples and kiwi leave a rough feeling on the tongue?
gpt
Human skin contains oils which aid in blocking out the absorption of chemicals which would harm or irritate the skin. Those oils contain proteins. Pineapple contains a chemical compound called bromelain which has the ability to break down these proteins. This enzyme is called a protease. Kiwis also contain a protease called actinidin.

Because these enzymes readily breaks down proteins, bromelain is frequently used as a natural meat tenderizer. In addition, they may also induce a prickly sensation in the mouth when consumed.

In pineapples the enzyme is present in all parts of the plant, it's most concentrated in the stem, the hard piece in the middle of the fruit, which is much more fibrous and chewy but still edible.