Abstract #W141

# W141
Characterization of single crystals in the rinds of white mold and smear ripened cheeses with single crystal X-ray diffractometry.
Gil F. Tansman*1, Paul S. Kindstedt1, John M. Hughes2, 1Department of Nutrition and Food Sciences, University of Vermont, Burlington, VT, 2Department of Geology, University of Vermont, Burlington, VT.

Calcium-containing crystals that form in the rinds of soft surface-ripened cheeses are thought to contribute to cheese softening through the removal of calcium from the aqueous and colloidal states. Several researchers have observed crystals near the surface of bloomy rind cheeses but none have succeeded in identifying them. The present work was conducted in parallel with a powder X-ray diffraction (PXRD) study in which fresh cheese samples were analyzed for total crystalline composition. In contrast, this study used single crystal X-ray diffraction (SCXRD) and polarized light microscopy to identify individual crystals isolated from cheese rinds and surface smears to obtain chemical information about crystal structure and atomic uniformity. Four Vermont soft surface ripened cheeses were obtained from commercial sources; 2 of these cheeses were bloomy rind (white mold) varieties and 2 were smear ripened varieties. Samples from 1mm below the rinds of all 4 cheeses as well as scrapings of the washed rind surface smears were mounted on glass microscope slides and observed with a petrographic polarized light microscope. Rotation of the circular microscope stage allowed crystal extinction to be observed. Three distinct crystals were observed by comparing crystal morphologies and extinction variability. Two different crystals were observed in the smears (one smear exhibited only one of the crystals) and one entity was observed 1mm beneath the rind in all 4 cheeses. Nearly all crystals that had not been damaged in the mounting process exhibited uniform extinction indicating that they were single crystals. Single crystals from the smears and from beneath the fungal bloom were isolated with a dissection needle and mounted on a goniometer head for analysis with a single crystal diffractometer. Structures for crystals in the smears were determined for ikaite (CaCO3·6H2O) and struvite (NH4MgPO4·6H2O), and a crystal structure for calcite (CaCO3) was determined from a bloomy rind crystal, thereby corroborating the results of the parallel PXRD study. This is the first observation of single crystals in cheese.

Key Words: cheese, crystal, single crystal x-ray diffraction (SCXRD)