INS 511 is magnesium chloride, numbered E511 in Europe. It is obtained from seawater and natural brines, and it is the main component of nigari, the bitter liquid left after sea salt is made, long used in Japan to set tofu. Codex lists it as a colour retention agent, firming agent and stabilizer.
Like calcium salts, magnesium ions can link with proteins and pectins, which is why magnesium chloride firms tofu and some vegetable products. It has a noticeably bitter taste, so it is used in small amounts.
On SeekSnack it appears in Chocobi Corn Snacks - Chocolate, a chocolate corn snack whose label groups it with calcium carbonate (INS 170 (i)) under stabilizing agent.
