Food Structure


B. E. Brooker


Samples of several different types of mouldripened cheese were examined by light and electron microscopy for evidence of calcium phosphate crystallization near their surfaces , which, it was predicted , should result from the pH changes that take place in the rind during ripening . Transmission electron microscopy showed that characteristic convoluted crystals appeared in the rind as mould growth developed and that there was good evidence that at least some of the crystal nucleation was taking place inside effete hyphae. Light microscopy showed that this coincided with the appearance of birefringent, phosphate-rich crystals in the cheese rind which were tentatively identified as calcium phosphate. This was confirmed by a ser ies of experiments in which frozen and fractured cheese was examined by scanning electron microscopy in conjunction with digital X-ray spectrometry . This showed that the rind contained very high levels of calcium and phosphorus which could not be attributed to surface drying because in the same area, there was no corresponding concentration of other elements, such as chlorine.

It is proposed that the high pH generated by the surface flora causes the precipitation of calcium phosphate from the continuous aqueous phase . In addition, the inhibitory effect of casein on the phase transformation to crystalline calcium phosphate is probably removed by the action o f extracellular proteases from the mould. The resulting depletion of calcium phosphate in the aqueous phase establishes a gradient which is responsible for the diffusion of more of the salt from deeper parts of the cheese and the progressive concentration in the rind.

Included in

Food Science Commons