Characterization and freeze-drying of cheese fractions

This study aimed to characterise seven cheese fractions, in order to allow their freezing and freeze-drying as a mean to preserve their microbial population for a long time. It is included in a larger research project, intending the preservation of the biodiversity of cheese microbial ecosystems. The lactose, galactose, lactic acid, calcium, sodium chloride and total nitrogen concentrations, as well as the dry matter and the fat content were determined. The physico-chemical characteristics of pH, water activity and water content, and the thermal properties of crystallisation, melting and glass transition temperatures were evaluated. A statistical analysis showed good correlation between the thermal properties and the composition and the physico-chemical characteristics. The cheese fractions were classified according to their glass transition and melting temperatures. Natural liquid starters were characterised by high melting and phase transition temperatures and a low dry matter. Fresh cheese curds were distinguished by a high lactic acid concentration, a low phase transition temperature and a high melting temperature. The salted curds showed similar characteristics but lower carbohydrates content and higher NaCl concentration. Finally, the cheese rinds were identified by low melting and phase transition temperatures and a high dry matter. According to these properties, the liquid starters were suitable for freezing at -80 degrees C, whereas the curds and the rinds should be frozen at -196 degrees C. The freeze-drying of the cheese fractions was done successfully. The freeze-dried starters should be stored at 4 degrees C whereas the storage temperature of the cheese curds and rinds should not excess -20 degrees C.