Effect of tetrasodium pyrophosphate concentration and cooking time on the physicochemical properties of process cheese.

Tetrasodium pyrophosphate (TSPP) is widely used as an emulsifying salt (ES) in process cheese. Previous reports have indicated that TSPP exhibits some unusual properties, including the gelation of milk proteins at specific ES concentrations. We studied the effect of various concentrations (0.25-2.75%) of TSPP and cooking times (0-20min) on the rheological, textural, and physical properties of pasteurized process Cheddar cheese using a central composite rotatable experimental design. Cheeses were made with a constant pH value to avoid pH as a confounding factor. Modeling of the textural properties of process cheese made with TSPP exhibited complex behavior, with polynomial models (cubic) giving better predictions (higher coefficient of determination values) than simpler quadratic models. Meltability indices (degree of flow from the UW MeltProfiler (University of Wisconsin-Madison), loss tangent value at 60°C from rheological testing, and Schreiber melt area) initially decreased with increasing TSPP concentrations, but above a critical ES concentration (~1.0%) meltability increased at higher TSPP concentrations. The storage modulus values measured at 70°C for process cheese initially increased with increasing TSPP concentration, but above a concentration of 1% ES, the storage modulus values decreased. Cooking time had little effect on the various melting or rheological properties. With an increase in TSPP concentration, the insoluble Ca and P contents increased, suggesting that TSPP addition resulted in the formation of insoluble calcium pyrophosphate complexes; some of which were likely associated with caseins. A portion of the added TSPP remained in the soluble phase. The acid-base buffering profiles also indicated that calcium pyrophosphate complexes were formed in cheese made with TSPP. In milk systems, low levels of TSPP have been shown to induce protein crosslinking and gelation, whereas at higher TSPP concentrations milk gelation was inhibited due to excessive charge repulsion from these calcium pyrophosphate complexes. We hypothesized that a similar phenomenon was occurring in our process cheese, resulting in the initial reduction in meltability with TSPP addition due to protein crosslinking, but at higher TSPP levels meltability increased due to excessive charge repulsion.

Effect of sodium hexametaphosphate concentration and cooking time on the physicochemical properties of pasteurized process cheese.

Sodium hexametaphosphate (SHMP) is commonly used as an emulsifying salt (ES) in process cheese, although rarely as the sole ES. It appears that no published studies exist on the effect of SHMP concentration on the properties of process cheese when pH is kept constant; pH is well known to affect process cheese functionality. The detailed interactions between the added phosphate, casein (CN), and indigenous Ca phosphate are poorly understood. We studied the effect of the concentration of SHMP (0.25-2.75%) and holding time (0-20min) on the textural and rheological properties of pasteurized process Cheddar cheese using a central composite rotatable design. All cheeses were adjusted to pH 5.6. The meltability of process cheese (as indicated by the decrease in loss tangent parameter from small amplitude oscillatory rheology, degree of flow, and melt area from the Schreiber test) decreased with an increase in the concentration of SHMP. Holding time also led to a slight reduction in meltability. Hardness of process cheese increased as the concentration of SHMP increased. Acid-base titration curves indicated that the buffering peak at pH 4.8, which is attributable to residual colloidal Ca phosphate, was shifted to lower pH values with increasing concentration of SHMP. The insoluble Ca and total and insoluble P contents increased as concentration of SHMP increased. The proportion of insoluble P as a percentage of total (indigenous and added) P decreased with an increase in ES concentration because of some of the (added) SHMP formed soluble salts. The results of this study suggest that SHMP chelated the residual colloidal Ca phosphate content and dispersed CN; the newly formed Ca-phosphate complex remained trapped within the process cheese matrix, probably by cross-linking CN. Increasing the concentration of SHMP helped to improve fat emulsification and CN dispersion during cooking, both of which probably helped to reinforce the structure of process cheese.

Effects of pH on the textural properties and meltability of pasteurized process cheese made with different types of emulsifying salts.

Functional properties of pasteurized process cheese (PPC) made with different types of emulsifying salts (ES) (2%, wt/wt) were investigated as a function of different pH values (from 5.3 to approximately 5.9). The ES investigated were trisodium citrate (TSC), disodium phosphate (DSP), sodium hexametaphosphate (SHMP), and tetrasodium pyrophosphate (TSPP). Meltability and textural properties were determined using UW-MeltProfiler and uniaxial compression, respectively. All PPC samples exhibited an increase in degree of flow (DOF) determined at 45 degrees C when the pH was increased from 5.3 to 5.6, presumably reflecting greater Ca binding by the ES, increased charge repulsion and therefore greater casein dispersion. When the pH of PPC was increased from 5.6 to approximately 5.9, 2 types of ES (DSP and SHMP) exhibited no further increase in DOF at 45 degrees C; while DOF increased in 1 type of PPC (made with TSC) but decreased in another (made with TSPP). TSPP is able to form crosslinks with casein especially in the vicinity of pH 6, which likely restricted melt; in contrast TSC does not crosslink caseins and the increase in pH helped cause greater casein dispersion. Low pH samples (5.3) were not significantly harder than higher pH samples for all ES types but exhibited fracture. The PPC with the highest hardness values at pHs 5.3 and 5.6 were made with TSPP and TSC, respectively. The pH-dependent functional behavior of PPC was strongly influenced by the type of ES and its physicochemical properties including its ability to bind Ca, the possible creation of crosslinks with casein and casein dispersion during cooking.

Effect of trisodium citrate concentration and cooking time on the physicochemical properties of pasteurized process cheese.

The effects of the concentration of trisodium citrate (TSC) emulsifying salt (0.25 to 2.75%) and holding time (0 to 20 min) on the textural, rheological, and microstructural properties of pasteurized process Cheddar cheese were studied using a central composite rotatable design. The loss tangent parameter (from small amplitude oscillatory rheology), extent of flow (derived from the University of Wisconsin Meltprofiler), and melt area (from the Schreiber test) all indicated that the meltability of process cheese decreased with increased concentration of TSC and that holding time led to a slight reduction in meltability. Hardness increased as the concentration of TSC increased. Fluorescence micrographs indicated that the size of fat droplets decreased with an increase in the concentration of TSC and with longer holding times. Acid-base titration curves indicated that the buffering peak at pH 4.8, which is due to residual colloidal calcium phosphate, decreased as the concentration of TSC increased. The soluble phosphate content increased as concentration of TSC increased. However, the insoluble Ca decreased with increasing concentration of TSC. The results of this study suggest that TSC chelated Ca from colloidal calcium phosphate and dispersed casein; the citrate-Ca complex remained trapped within the process cheese matrix. Increasing the concentration of TSC helped to improve fat emulsification and casein dispersion during cooking, both of which probably helped to reinforce the structure of process cheese.