Water partitioning in Mozzarella cheese and its relationship to cheese meltability

The aim of this study was to determine what happens to water in Mozzarella cheeses during storage and to relate those changes to cheese microstructure and functionality. A reduced fat (8% fat) Mozzarella cheese and a control cheese with 19% fat were made and evaluated over 21 d of refrigerated storage at 4 degrees C. Fat, protein, ash, salt, and water were measured on d 1. Meltability, total water, freezable water, and expressible water were measured on d 1, 7, 14, and 21. Even though the reduced fat cheese had a higher total water content than did the control cheese, the reduced fat cheese contained less water on a fat-free basis. The amount of water expressible at 25 degrees C was higher in the control cheese than in the reduced fat cheese and was proportional to the fat content of the cheese. During storage, the expressed serum for both cheeses decreased to zero by d 21. Based on changes observed in microstructure of a commercial Mozzarella cheese (19% fat) during storage, we concluded that the expressed water was derived from water contained in the fat-serum channels that were interspersed throughout the protein matrix. The amount of bound water was lower in the control cheese than in the reduced fat cheese and was proportional to the protein content of the cheese. Bound water levels remained constant throughout storage. During storage of the commercial Mozzarella cheese, the fat-serum channels became smaller with the protein matrix expanding into the areas between the fat globules. By d 21, the fat globules were completely encased by the protein matrix. This expansion of the protein matrix in the commercial cheese occurred over the same time span as the decrease in expressible water of the experimental cheese and indicated that the protein matrix was absorbing the water originally located in the fat-serum channels. Because no change in bound water was observed, the water that had been expressible at d 1 was being absorbed into the protein matrix as entrapped water. The meltability of both cheeses increased during storage while the percentage of entrapped water increased.