Minerals in Food: Crystal Structures of Ikaite and Struvite from Bacterial Smears On Washed-rind Cheese

Food contains inorganic elements and compounds that are important for human nutrition and human health. Although these substances have been investigated and characterized in many foods for their nutritive value, little is known about the crystal phases that form in foods. In this study, we investigated crystals that form in the bacterial smears on the surface of washed-rind cheese. Washed-rind cheeses have been consumed for centuries, but the crystals that often contribute detectable grittiness to the surface of these cheeses have never been identified. The crystals were characterized with petrographic microscopy and identified with single crystal X-ray diffractometry as ikaite (CaCO₃·6H₂O), a rare metastable phase that has only been observed in freezing marine and lacustrine environments, and struvite (NH₄MgPO₄·6H₂O), a mineral that is often associated with bacterial activity. These crystals are important to cheesemakers because they affect cheese texture and sensory characteristics. The potential importance of the bacterial smear in the nucleation of these phases is discussed, and the possibility of using cheese as a model system to investigate geological biomineralization phenomena is explored.