Effects of pH on the Textural Properties and Meltability of Pasteurized Process Cheese Made with Different Types of Emulsifying Salts

ABSTRACT: 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 °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 °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.     

Effects of two types of emulsifying salts on the functionality of nonfat pasta filata cheese

Effects of 2 types of emulsifying salts (ES) on the functionality of nonfat pasta filata cheese were examined. Nonfat pasta filata cheese was made from skim milk by direct acidification. Trisodium citrate (TSC) and tetrasodium pyrophosphate (TSPP) were added to curds (at 1, 3, and 5%, wt/wt) at the dry-salting step, together with glucono-δ-lactone to maintain a constant pH. When TSC was added, there were no significant compositional differences, although insoluble Ca and P contents significantly decreased with the addition of TSC. When TSPP was added, fat content was not significantly different, but protein content decreased with increasing concentrations of TSPP. Both insoluble Ca and P contents increased with the addition of 1% TSPP. The addition of ES affected textural and functional properties. With increasing concentrations of TSC, meltability increased, whereas increasing the TSPP content decreased meltability. Cheese made with 1% TSC had better stretchability compared with control cheese. However, the addition of more than 3% TSC decreased stretchability. Addition of TSPP caused a considerable decrease in stretchabilty. Scanning electron microscopy revealed that the size and number of serum pockets decreased and protein appeared more hydrated with the addition of both ES. These results suggested that TSC and TSPP influenced the functionality of nonfat pasta filata cheese differently; that is, the effects of TSC were probably caused by a decrease in the number of colloidal calcium phosphate cross-links and an increase in electrostatic repulsion, whereas the effects of TSPP may have been related to the formation of new TSPP-induced casein-casein interactions.     

Effects of emulsifying salts on the turbidity and calcium-phosphate-protein interactions in casein micelles

Influence of emulsifying salts (ES) on some physical properties of casein micelles was investigated. A reconstituted milk protein concentrate (MPC) solution (5% wt/wt) was used as the protein source and the effects of ES [0 to 2.0% (wt/wt)] were estimated by measuring turbidity, acid-base titration curves and amount of casein-bound Ca and inorganic P (P_i). Various ES, trisodium citrate (TSC), or sodium phosphates (ortho-, pyro-, or hexameta-) were added to MPC solution, and all samples were adjusted to pH 5.8. Acid-base buffering curves were used to observe changes in the amount and type of insoluble Ca phosphates. An increase in the concentration of TSC added to MPC solution decreased turbidity, buffering at pH ∼5 (contributed by colloidal Ca phosphate), and amount of casein-bound Ca and P_i. Addition of up to 0.7% disodium orthophosphate (DSP) did not significantly influence turbidity, buffering curves, or amount of casein-bound Ca and P_i. When higher concentrations (i.e., ≥1.0%) of DSP were added, there was a slow decrease in turbidity. With increasing concentration of added tetrasodium pyrophosphate (TSPP), turbidity and buffering at pH ∼5 decreased, and amount of casein-bound Ca and P_i increased. When small concentrations (i.e., 0.1%) of sodium hexameta-phosphate were added, effects were similar to those when TSPP were added but when higher concentrations (i.e., ≥0.5%) were added, the buffering peak shifted to a higher pH value, and amount of casein-bound Ca and P_i decreased. These results suggested that each type of ES influenced casein micelles by different mechanisms.     

Effect of the type of emulsifying salt on microstructure and rheological properties of "requeijão cremoso" processed cheese spreads

Abstract: The role of different types of emulsifying salts—sodium citrate (TSC), sodium hexametaphosphate (SHMP), sodium tripolyphosphate (STPP) and tetrasodium pyrophosphate (TSPP)—on microstructure and rheology of “requeijão cremoso” processed cheese was determined. The cheeses manufactured with TSC, TSPP, and STPP behaved like concentrated solutions, while the cheese manufactured with SHMP exhibited weak gel behavior and the lowest values for the phase angle (G”/G’). This means that SHMP cheese had the protein network with the largest amount of molecular interactions, which can be explained by its highest degree of fat emulsification. Rotational viscometry indicated that all the spreadable cheeses behaved like pseudoplastic fluids. The cheeses made with SHMP and TSPP presented low values for the flow behavior index, meaning that viscosity was more dependent on shear rate. Regarding the consistency index, TSPP cheese showed the highest value, which could be attributed to the combined effect of its high pH and homogeneous fat particle size distribution.     

The effect of composition of ternary mixtures containing phosphate and citrate emulsifying salts on selected textural properties of spreadable processed cheese

Ternary mixtures consisting of phosphate and citrate emulsifying salts were studied for their impact on selected textural properties (especially hardness) of processed cheese spreads over a 30 day storage period at 6 ± 2 °C. Two different groups of samples were manufactured, one with pH adjustment (target values within the interval of 5.60–5.80) and one without pH adjustment. When binary mixtures with trisodium citrate (TSC) and tetrasodium diphosphate (TSPP) were used (with zero content of the other salts tested in the ternary mixture), the products consisting of TSC and TSPP at a ratio of approximately 1:1 were the hardest. Increasing the content of TSC, TSPP and/or sodium salt of polyphosphate and decreasing that of disodium hydrogen phosphate (DSP) in ternary mixtures resulted in the increasing of the hardness of processed cheese. The absolute values of processed cheese hardness significantly changed as a result of pH adjustment.     

Zinc binding in bovine milk

About 90% of the Zn in bovine skim milk was sedimented by ultracentrifugation at 100,000 g for 1 h. About half of the non-sedimentable Zn was non-dialysable, indicating that it was associated with protein, probably non-sedimented casein micelles. Casein micelles incorporated considerable amounts of Zn added to skim milk as ZnCl2, and at Zn concentrations greater than or equal to 16 mM coagulation of casein micelles occurred. Ca was displaced from casein micelles by increasing ZnCl2 concentration and approximately 40% of micellar Ca was displaced by 16 mM-ZnCl2. Micellar Zn, Ca and Pi were gradually rendered soluble as the pH of milk was lowered and at pH 4.6 greater than 95% of the Zn, Ca and Pi were non-sedimentable. These changes were largely reversible by readjustment of the pH to 6.7. About 40% of the total Zn in skim milk was non-sedimentable at 0.2 mM-EDTA and most of the remainder was gradually rendered soluble by EDTA over the concentration range 1-50 mM. This indicates that there are two distinct micellar Zn fractions. No micellar Ca or Pi was solubilized at EDTA concentrations up to 1.0 mM, indicating that both colloidal calcium phosphate (CCP) and casein micelles remained intact under conditions where the more loosely bound micellar Zn fraction dissolved. Depletion of casein micelles of colloidal Ca and Pi by acidification and equilibrium dialysis resulted in removal of Zn, and in colloidal Pi-free milk non-dialysable Zn was reduced to 1.2 mg/l (approximately 32% of the original Zn). Thus, approximately 32% of the Zn in skim milk is directly bound to caseins, while approximately 63% is associated with CCP. Over 80% of the Zn in colloidal Pi-free milk was rendered soluble by 0.2 mM-EDTA, indicating that the casein-bound Zn is the loosely bound Zn fraction in casein micelles. A considerable fraction of the Zn in acid whey (pH 4.6) co-precipitated with Ca and Pi on raising the pH to 6.7 and heating for 2 h at 40 degrees C, indicating that insoluble Zn phosphate complexes form readily under these conditions. Studies on dialysis of milk against water, or dilution of milk or casein micelles with water, showed that CCP and its associated Zn is very stable and dissolves only very slowly at pH 6.6. The nature of Zn binding in casein micelles may help to explain the lower nutritional bioavailability of Zn in bovine milk and infant formulae compared with human milk.     

The use of sedimentation field flow fractionation and photon correlation spectroscopy in the characterization of casein micelles

Sedimentation Field Flow Fractionation (SdFFF) was combined with Photon Correlation Spectroscopy (PCS), to characterize changes in the structure of the colloidal particles of reconstituted skim milk of diameter >50 nm (aggregates of casein and calcium phosphate known as casein micelles) with the changes in partitioning (with the addition of salt) of calcium (Ca), inorganic phosphate (Pi) and casein between the serum and colloidal phases of the milk. The number weighted particle size distributions are determined. These are well represented by a log-normal distribution. Methods are presented for estimating the relative contributions of scattering and absorbance to the SdFFF detector signal and for taking both into account when analysing SdFFF data. The values found for the effective density of the casein micelles were in good agreement with the literature and ranged from (1.06-1.08 g cm(-3)) according to the composition of micelles. The changes in the scattering intensity as determined by PCS correlated with the changes in the particle composition. Although the concentrations of colloidal calcium phosphate (CCP) (1.1-3.5 g/kg milk) and micellar casein (18.1-27.2 g/kg milk) varied considerably only small changes in the size distribution of particles >50 nm diameter were observed except for milk to which 30 mmol Pi+10 mmol Ca/kg milk had been added where the particle size distribution shows a swelling of the particles consistent with a lower than expected value for the particle density. These observations suggest that the micelles have the ability to both lose (depleted micelles) and accommodate (enriched micelles) more casein, calcium and inorganic phosphate in their interior, thus confirming the model of the micelles which postulates an open structure allowing freedom of movement of casein and small ions.     

Effects of enhancement with differing phosphate types, concentrations, and pump rates, without sodium chloride, on beef biceps femoris instrumental color characteristics

Enhancement of beef biceps femoris muscles (n=45) with solutions comprising sodium hexametaphosphate (SHMP), sodium tripolyphosphate (STPP), or tetrasodium pyrophosphate (TSPP) at either 0.2% or 0.4% of product weight, with the exclusion of sodium chloride, was performed to observe the independent phosphate effects on instrumental color during simulated retail display. All solutions were injected into muscle samples at either 112% (12% pump) or 118% (18% pump) of raw product weight. All three phosphate types maintained higher (P<0.05) L* values than untreated steaks (CNT) through 5 days-of-display, and SHMP had higher (P<0.05) L* values than STPP and TSPP through 7 days-of-display. Additionally, steaks with 0.2% phosphate inclusion were lighter (L*; P<0.05) than CNT throughout display, and were lighter (P<0.05) than steaks enhanced with 0.4% phosphates through 7 days of display. Steaks enhanced with TSPP had higher (P<0.05) a* values than CNT on days 5 and 7 of display, whereas SHMP- or STPP-enhanced steaks generally had similar (P>0.05) a* values as CNT after 3d of display. Direct comparison of phosphate concentrations revealed no differences (P>0.05) in a* values. Only steaks enhanced with TSPP were more vivid (P<0.05) and had higher (P<0.05) proportions of oxymyoglobin than CNT on days 5 and 7 of display. However, direct comparison of phosphate types indicated that TSPP- and STPP-enhanced steaks had similar (P>0.05) oxymyoglobin proportions during display. Phosphate inclusion at 0.4% maintained higher (P<0.05) oxymyoglobin proportions than 0.2% phosphate inclusion through 5 days-of-display. These results indicate that while 0.2% phosphate concentrations maintain lighter color, 0.4% concentrations can more effectively retain oxymyoglobin during display. Additionally, only steaks enhanced with TSPP were redder, more vivid, and had higher oxymyoglobin proportions than untreated steaks during the latter stages of display.     

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 (0-20 min) 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.     

Selected Quality Factors and Sensory Attributes of Cured Ham as Influenced by Different Phosphate Blends

In each of four replications, 32 packer-style hams were randomly allotted to one of eight treatment groups in which the curing brine formulated for a 10% pump contained: (1) No phosphate; (2) 100% sodium tripolyphosphate (STP); (3) 5% sodium hexametaphosphate (SHMP) + 95% STP; (4) 10% SHMP + 90% STP; (5) 5% Quadrafos (SQ) + 95% STP; (6) 10% SQ + 90% STP; (7) 10% tetrasodium pyrophosphate (TSPP) + 90% STP; or (8) 20% TSPP + 80% STP. Raw hams were subjectively evaluated for quality, samples were removed for analysis, and hams were processed according to commercial procedures. Processing losses and cooking losses were calculated, and physical and sensory properties of the processed, cooked hams were measured. The 20% TSPP blend was least effective in reducing processing shrinkage; whereas, the 5% SHMP blend was the most effective. Nonphosphate treated hams had greater cooking losses and were scored lowest for all sensory attributes. Greater drip cooking losses occurred as amounts of SHMP and SQ increased in the phosphate blends.     

Effects of enhancement with varying phosphate types and concentrations, at two different pump rates on beef biceps femoris instrumental color characteristics

The effect of enhancing beef biceps femoris muscles (n=45) with solutions comprising 2.0% sodium chloride and either sodium hexametaphosphate (SHMP), sodium tripolyphosphate (STPP), or tetrasodium pyrophosphate (TSPP) at either 0.2% or 0.4% of product weight on instrumental color during simulated retail display was investigated. All solutions were injected into muscle samples at either 112% (12% pump) or 118% (18% pump) of raw product weight. Muscles treated with all three phosphate types had lower (P<0.05) L* and b* values compared to untreated muscles (CNT). Steaks enhanced with STPP had similar (P>0.05) a* values as CNT, whereas SHMP- and TSPP-treated steaks generally had lower a* values than CNT. Across phosphate type, excluding day 3 of display, steaks treated with phosphate at 0.4% had similar (P>0.05) a* values as CNT, whereas those with 0.2% phosphate addition had lower (P<0.05) a* values than CNT. Across five days of display, STPP maintained higher (P<0.05) a* values than steaks treated only with sodium chloride, whereas SHMP did not differ (P>0.05) from sodium chloride-treated steaks. While STPP maintained a similar (P>0.05) saturation index as CNT, SHMP and TSPP generally had decreased (P<0.05) vividness during display. Additionally, excluding day 3 of display, phosphate concentration at 0.4% maintained similar vividness as CNT, whereas 0.2% phosphate concentration caused decreased (P<0.05) vividness, compared to CNT. The 630/580nm ratio results indicated that SHMP had less (P<0.05) oxymyoglobin than CNT throughout display. Disregarding day 3 of display, both STPP and TSPP had similar (P>0.05) oxymyoglobin proportions as CNT. These results indicate that STPP was the most effective phosphate type for maintaining color. Additionally, 0.4% phosphate concentrations can maintain color better than 0.2% phosphate concentrations. However, none of the phosphate/salt combinations produced superior color, compared to untreated steaks.     

Enhancement with varying phosphate types, concentrations, and pump rates, without sodium chloride on beef biceps femoris quality and sensory characteristics

Beef biceps femoris muscles (n=45) were used to evaluate the effect of enhancement with solutions containing sodium hexametaphosphate (SHMP), sodium tripolyphosphate (STPP), or tetrasodium pyrophosphate (TSPP) at either 0.2% or 0.4% of product weight, without sodium chloride. All solutions were injected into muscle samples at either 112% (12% pump) or 118% (18% pump) of raw product weight. Muscles enhanced with STPP or TSPP had a higher (P<0.05) pH than SHMP or untreated muscles (CNT), whereas there was no difference (P>0.05) in pH between SHMP and CNT. Muscles enhanced with STPP had less (P<0.05) free water than CNT, whereas SHMP and TSPP did not differ from CNT. However, direct comparison of phosphate types revealed no difference (P>0.05) in free water. Steaks enhanced with SHMP had greater (P<0.05) cooking losses than CNT, whereas steaks treated with STPP or TSPP did not differ (P>0.05) from CNT. Phosphate inclusion at 0.2% allowed for greater (P<0.05) cooking losses than CNT, whereas 0.4% phosphate inclusion exhibited similar (P>0.05) cooking losses as CNT. Although there were no differences (P>0.05) in cooking loss between pump rates, steaks enhanced at an 18% pump rate had greater (P<0.05) cooking losses than CNT, whereas those enhanced at 12% had similar (P>0.05) cooking losses as CNT. Enhancement with any of the three phosphate types or either concentration did not improve (P>0.05) sensory tenderness or juiciness characteristics compared to CNT, but enhancement at an 18% pump rate allowed for improved (P<0.05) overall tenderness, compared to a 12% pump rate. These results suggest that while phosphate enhancement independent of sodium chloride generally did not improve water retention, cooked yields and palatability compared to untreated samples, utilizing higher phosphate concentrations or utilizing STPP or TSPP effectively retained the additional water associated with solution enhancement, allowing for similar free water and cook yields as untreated samples.     

Effect of calcium chelators on physical changes in casein micelles in concentrated micellar casein solutions

The effect of calcium chelators on physical changes of casein micelles in concentrated micellar casein solutions was investigated by measuring calcium-ion activity, viscosity and turbidity, and performing ultracentrifugation. The highest viscosities were measured on addition of sodium hexametaphosphate (SHMP), because it cross-linked the caseins. For the weak calcium chelator disodium uridine monophosphate (Na₂UMP), physical changes in the solutions were negligible. Disodium hydrogen phosphate (Na₂HPO₄), trisodium citrate (TSC), and sodium phytate (SP) caused similar increases in viscosity, but had different effects on turbidity. The increase in viscosity was attributed to swelling of the casein micelles (i.e., increased voluminosity) at decreasing calcium-ion activity. The major decrease in turbidity was due to dissociation of the casein micelles. The extent of micellar dissociation was dependent on the type and concentration of calcium chelator. It seems that the micelles were dissociated in the order of SHMP ≥ SP > TSC > Na₂HPO₄ > Na₂UMP.     

Rennet-induced gelation of calcium and phosphate supplemented skim milk subjected to CO2 treatment

A Doehlert design was performed to study the effect of calcium and phosphate supplementation at 0 to 25 mmol/kg and 0 to 16 mmol/kg, respectively, on the rennet gelation of reconstituted skim milk subjected to pH-reversible CO(2) acidification. Supplemented reconstituted skim milk samples were acidified to pH 5.80 by the addition of CO(2) under pressure and depressurized under vacuum to restore the initial pH value. The second-order polynomial models satisfactorily predicted the effect of salt addition on the micellar molar Ca:P ratio and the average diameter of the casein micelles, whereas only trends were used in the analysis of the rennet-clotting behavior of salt-supplemented, CO(2)-treated milk. Whether added Ca was the most determinant factor on the micellar molar Ca:P ratio, added Pi (a mixture of Na(2)HPO(4) and NaH(2)PO(4)) was the most determinant factor on the other responses studied, and its effect was most pronounced when Ca was simultaneously added. By comparison with control samples, changes observed in this study were essentially due to salt supplementation and not to the CO(2) treatment. Therefore, this CO(2) treatment could be considered as an entirely reversible treatment rather than only pH-reversible, and predictions might be applied to untreated milk. In the case of Ca-supplemented milk, the micellar molar Ca:P ratio increased, the average micellar diameter decreased, and the rennet-clotting properties were improved, whereas opposite effects were observed upon Pi supplementation. Since modification of the micellar molar ratio is the result of change in the chemical composition of micellar calcium phosphate, the effect of calcium and phosphate supplementation on the rennet clotting of milk was found to be also dependent on the nature of the interaction between caseins and colloidal calcium phosphate.     

CHEMICAL AND FUNCTIONAL PROPERTIES OF VARIOUS BLENDS OF PHOSPHATES

Chemical and functional properties of various blends of phosphate were examined and compared with the conventional phosphate (M-CP: a mechanical blend [50:50] of sodium tripolyphosphate [STPP] and tetrasodium pyrophosphate [TSPP]). Regardless of solution temperature and brine concentration, the solubilities of various blends of phosphates, especially M-1 (a mechanical blend [50:50] of tetrapotassium pyrophosphate and STPP), M-LC (a long-chained sodium hexametapolyphosphate [SHMP] treated with trisodium phosphate [TSP]) and M-MC (a middle-chained SHMP treated with TSP), except for C-S (a chemical blend [50:50] of STPP and TSPP for faster/higher solubility) and C-V (a chemical blend [50:50] of STPP and TSPP for higher viscosity), were higher than that of M-CP. The scanning electronic microscopic image revealed that the structures of various blends of phosphate were quite different. Comparing with M-CP, C-V was superior in viscosity, water retention ability (WRA), emulsifying activity and cooking stability. M-1 was superior in WRA compared to M-CP.

PRACTICAL APPLICATIONS

Conventional blending for phosphates is typically made through simple mechanical mixing. In our study, we featured chemically blended phosphates and found that some of them demonstrated superior functional properties. With this advantage, the use of chemically blended phosphate could reduce the usage level while achieving a similar or better performance.     

Effects of calcium chelating agents on the solubility of milk protein concentrate

The aim of this study was to determine the effects of calcium chelating agents on the dissolution and functionality of 10% (w/w) milk protein concentrate (MPC) powder. MPC powder dissolution rate and solubility significantly (P > 0.05) increased with addition of sodium phosphate, trisodium citrate (TSC) and sodium hexametaphosphate (SHMP), compared to MPC dispersions alone. Trisodium citrate and SHMP addition increased viscosity as a result of micelle swelling. However, dispersions containing SHMP showed a decrease in viscosity after prolonged time due to micelle dissociation. Overall, MPC powder dissolution was aided by the addition of calcium chelating agents.     

Effects of phosphates and citrates on sediment formation in UHT goats' milk

Sediment formation was investigated during UHT treatment of goats' milk, subjected to indirect treatment at 140 degrees C for 2 s, with upstream homogenisation. Stabilisers evaluated were sodium hexametaphosphate (SHMP), trisodium citrate (TSC), disodium hydrogen orthophosphate (DSHP), and sodium dihydrogen orthophosphate (SDHP). With no added stabiliser, goats' milk produced a heavy sediment on UHT treatment. Addition of SDHP reduced pH, had little effect on ionic calcium and did not substantially reduce sediment. However, addition of SHMP, DSHP and TSC each reduced ionic calcium, increased ethanol stability and reduced sediment. Following stabiliser additions, there was a good correlation between ethanol stability and ionic calcium (R2=0.85) but not between ethanol stability and pH (R2=0.08). Overall, reducing ionic calcium reduced the amount of sediment formed for all these three stabilisers, although there was no single trend line between sediment formation and ionic calcium concentration. Sediment formation was not well correlated with pH for TSC or for SHMP, but it was for DSHP, making it the only stabiliser where sediment formation correlated well both with ionic calcium and pH, which might account for its effectiveness at higher ionic calcium levels. Sediment was much reduced when the temperature was reduced from 140 degrees C to 125 degrees C and 114 degrees C. There were no further changes in sediment on storage for two weeks. Analysis of the sediment showed that it was predominantly fat and protein, with a mass ratio ranging between 1.43:1 and 1.67:1. Its mineral content was usually less than 5% of dry weight. The maximum amounts of P and Ca were found to be 2.32% and 1.63%, respectively.     

Effects of mineral salts and calcium chelating agents on the gelation of renneted skim milk

The effects of adding CaCl2, orthophosphate, citrate, EDTA, or a mixture of these, to reconstituted skim milk (90 g of solids/kg solution) on the gelation of renneted milk were mediated by changes in Ca2+ activity and the casein micelle. At pH 6.65, the addition of citrate or EDTA, which removed more than 33% of the original colloidal calcium phosphate with the accompanying release of 20% casein from the micelle, completely inhibited gelation. Reformation of the depleted colloidal calcium phosphate and casein in the micelle, by the addition of CaCl2, removed this inhibition. When the minimum requirements for colloidal calcium phosphate and casein in the micelle were met, the coagulation time decreased with increasing Ca2+ activity, leveling off at high Ca2+ activity. The storage modulus of renneted gels, measured at 3 h, increased with increasing colloidal calcium phosphate content of micelles up to a level at which it was approximately 130% of the original colloidal calcium phosphate in the micelles. Further increases in colloidal calcium phosphate by the addition of CaCl2, orthophosphate, or mixtures of these, which did not change the proportion of casein in the micelle, decreased the storage modulus. The gelation of the renneted milk was influenced by Ca2+ activity, the amounts of colloidal calcium phosphate, and casein within the micelle, with the effects of colloidal calcium phosphate and casein within the micelle clearly dominating the storage modulus. These results are consistent with the model of Horne (Int. Dairy J. 8:171-177, 1998) which postulates that, following cleavage of the stabilizing K-casein hairs by rennet, the properties of the rennet gel are determined by the balance between the electrostatic and hydrophobic forces between casein micelles.     

Effects of sodium chloride, phosphate type and concentration, and pump rate on beef biceps femoris quality and sensory characteristics

Beef biceps femoris muscles (n=45) were used to evaluate the effect of enhancement with solutions comprising 2.0% sodium chloride and either sodium hexametaphosphate (SHMP), sodium tripolyphosphate (STPP), or tetrasodium pyrophosphate (TSPP) at either 0.2% or 0.4% of product weight. All solutions were injected into muscle samples at either 112% (12% pump) or 118% (18% pump) of raw product weight. Muscles treated with all three phosphate types had decreased (P<0.05) free water compared to untreated muscles (CNT), and while TSPP-treated muscles were able to bind greater (P<0.05) additional water than CNT, STPP- and SHMP-treated muscles did not differ (P>0.05) from CNT. Disregarding phosphate type, steaks with 0.4% phosphate inclusion bound more (P<0.05) water than those with 0.2% phosphate inclusion. Steaks treated with STPP or TSPP had decreased (P<0.05) cooking losses than CNT, while SHMP-treated steaks did not differ (P>0.05) from CNT. Steaks injected at 18% pump had greater (P<0.05) percent moisture, and did not differ (P>0.05) in free water, water binding, or cooking losses from steaks injected at 12% pump. Although there were no differences (P>0.05) in Warner-Bratzler shear force in this study, steaks with SHMP, STPP, and TSPP all were rated more tender, and juicier (P<0.05) by sensory panelists than CNT steaks or steaks enhanced only with sodium chloride. Regardless of phosphate type, steaks enhanced with 0.4% phosphate and those steaks at 18% pump received improved (P<0.05) sensory tenderness ratings compared to 0.2% phosphate and 12% pump, respectively. These results suggest that enhancing biceps femoris muscles with STPP or TSPP can improve water retention, yield, and palatability characteristics. Additionally, enhancement with a phosphate/salt solution at an 18% pump rate, compared to a 12% pump rate, can allow for improved sensory tenderness perceptions without decreasing product yields.     

Effect of Tetrasodium Pyrophosphate on the Physicochemical Properties of Yogurt Gels

The effect of tetrasodium pyrophosphate (TSPP) on the properties of yogurt gels was investigated. Various concentrations (0.05 to 0.2%) of TSPP were added to preheated (85°C for 30 min) reconstituted skim milk, which was readjusted to pH 6.50. Milk was inoculated with 2% starter culture and incubated at 42°C until the pH reached 4.6. Acid-base buffering profiles of milk and total and soluble calcium levels were measured. Turbidity measurements were used to indicate changes in casein dispersion. Storage modulus (G′) and loss tangent (LT) values of yogurts were monitored during fermentation using dynamic oscillatory rheology. Large deformation properties of gels were also measured. Microstructural properties of yogurt were observed using fluorescence microscopy. The addition of TSPP resulted in the disappearance of the buffering peak during acid titration at pH ∼5.1 that is due to the solubilization of colloidal calcium phosphate (CCP), and a new peak was observed at lower pH values (pH 4.0-4.5). The buffering peak at pH 6.0 during base titration virtually disappeared with addition of TSPP and a new peak appeared at pH ∼4.8. The addition of TSPP reduced the soluble Ca content of milk and increased casein-bound Ca values. The addition of up to 0.125% TSPP resulted in a reduction in turbidity because of micelle dispersion but at 0.15%, turbidity increased and these samples exhibited a time-dependent increase in turbidity because of aggregation of casein particles. Gels made with 0.20% TSPP were very weak and had a very high gelation pH (6.35), probably due to complete dispersion of the micelle structure in this sample. The LT value of gels at pH 5.1 decreased with an increase in TSPP concentration, probably due to the loss of CCP with the addition of TSPP. The G′ values at pH 4.6 of gels made with ≤0.10% TSPP were not significantly different but the addition of ≥0.125% TSPP significantly decreased G′ values. The addition of 0.05 to 0.125% TSPP to milk resulted in a reduction in the yield stress values of yogurt compared with yogurt made without TSPP. Greater TSPP levels (>0.125%) markedly reduced the yield stress values of yogurt. Lowest whey separation levels were observed in yogurts made with 0.10% TSPP. High TSPP levels (>0.10%) greatly increased the apparent pore size of gels. Addition of very low levels of TSPP to milk for yogurt manufacture may be useful in reducing the whey separation defect, but at TSPP concentrations ≥0.125% very weak gels were formed.