The acid element is highlighted here. Of course, you’re not going to look for chemicals, although, in molecular cuisine… You need elements that contain non-abrasive, milder acids, which are nevertheless able to penetrate the muscle fibers and relax them.
Lemon, red wine vinegar or cider vinegar will do the trick. Note that tomato, pineapple or papaya are excellent meat tenderizers! Thanks to lactic ferments: milk, cream, dairy products.
