This recipe for Chinese lemon chicken, and countless other Chinese recipes, use a technique known as velveting to tenderize meat.  Before cooking, meat is marinated in a mix of alkalinizing agents. It is usually a slurry of water and cornstarch, baking soda, and/or egg whites. Sometimes soy sauce and salt and pepper are added, but the primary idea is to alkalize. The result is the silkiest, most tender meat you can imagine.