Lloyd E. Metzger

Maintaining functional integrity during ultrafiltration-based concentration of milk protein concentrate (MPC) is as critical as achieving high solids in the retentate. Previous studies demonstrated that ultrafiltration in plate-and-frame filtration (PF) modules can effectively concentrate MPC derived from spiral-wound ultrafiltration (UF) of skim milk, particularly at elevated temperatures. This study compares the functionality of powdered MPCs produced via UF and PF systems. Skim milk retentate from UF containing 20% total solids and approximately 80% protein on dry basis (feed) was processed using PF modules equipped with flat-sheet membranes across 3 replicates. Three PF treatments were applied: PF22 at 22°C, PF50MS at 50°C targeting medium solids, and PF50HS at 50°C targeting high solids. Filtration for PF22 and PF50HS continued until transmembrane pressure reached 900 kPa, while PF50MS was terminated upon achieving ∼30% solids. Retentates from UF, PF22, PF50MS, and PF50HS were spray-dried and evaluated for rheological and functional properties. All reconstituted MPC powders exhibited pseudoplastic behavior, best described by the Herschel-Bulkley model. Functional assessments revealed that rennet coagulation time increased with PF temperature, necessitating the addition of ∼0.25% CaCl₂ to achieve timely coagulation. Elevated PF temperatures negatively affected other functional attributes, including increased wetting time, reduced solubility, and shortened heat coagulation time-most notably in PF50HS compared with PF22 and UF. Conversely, high-temperature PF enhanced emulsion stability without altering emulsion formation. All PF treatments improved foaming capacity while maintaining comparable foaming stability to UF. A slight reduction in whey protein content and increased protein denaturation was observed at higher PF temperatures. These findings underscore the importance of temperature optimization in preserving the functional properties of MPC during PF concentration.

In the typical milk protein concentrate (MPC) manufacturing process, skim milk is ultrafiltered using a spiral-wound membrane to produce MPC80 with ~20% total solids (TS) and 80% total protein (TP) on a DM basis. However, improving the production efficiency by achieving higher solids in the retentate has been a challenge when using spiral-wound membranes due to the limitation of operating pressure. We attempted flat-sheet UF membrane in a plate-and-frame (PF) module to concentrate the MPC further and achieve better production efficiency. Three replicates of ultrafiltered skim milk (feed) from spiral-wound UF membrane were concentrated in 3 different PF settings, including PF at 22°C (PF22), PF at 50°C for medium solids (PF50MS), and PF at 50°C for high solids (PF50HS). Hence there were total 4 treatments: feed, PF22, PF50MS, and PF50HS. Filtration was carried out until the pressure drop reached 900 kPa for PF22 and PF50HS. For the PF50MS, the filtration was stopped when the TS achieved close to 30%. The average permeate flux and final TS were significantly higher for the treatments conducted at 50°C compared with 22°C with permeate fluxes of 8.76, 10.50, and 11.18 Lm^-2h^-1 and TS of 26.83, 29.92, and 34.24%, respectively, for the PF22, PF50MS, and PF50HS treatments. The apparent viscosity of the final retentates was 577; 1,513; and 12,805 cP at a constant shear rate of 100 s^-1 for the PF22, PF50MS, and PF50HS treatments, respectively. Standard plate count increased in the high-temperature PF retentates; however, the level was below the acceptable limit as described in the USDA standards for fluid milk. This study determined that PF temperature is an important parameter for improving the filtration performance of MPC. The study establishes guidelines for increasing TS and protein levels in dairy foods production.

Processed cheese food (PCF) is a dairy product prepared by blending dairy ingredients with nondairy ingredients and heating the blend with agitation to produce a homogeneous product with an extended shelf life. Emulsifying salts (ES), such as disodium phosphate (DSP) and trisodium citrate, have a critical effect on the emulsification characteristics of casein by sequestering the calcium from the calcium-paracaseinate phosphate complex in natural cheese. Lactose-6-phosphate (LP) is an organic compound produced from lactose that has the potential to function as ES. Lactose-6-phosphate is not approved for use as a substitute for ES in the large-scale production of PC. The objective of this study was to produce PCF with LP instead of DSP. Lactose-6-phosphate was prepared by mixing 1 mol of α-lactose with 0.5 mol of sodium cyclo-triphosphate. The pH of recombined solutions was adjusted using sodium hydroxide to get a pH of 12 to obtain 60.74% LP. The solution was stirred for 3 d at room temperature and then concentrated to 52% total solids (TS). The ingredients in the PCF formulations were Cheddar cheese, butter, water, milk permeate powder, and LP (at a ratio of 2.0, 2.4, 2.8, 3.2, 4.0, 5.0, and 6.0%) were formulated to contain 17.0% protein, 25.0% fat, 44.0% moisture, and 2.0% salt. Processed cheese food made with 2.0% DSP was also produced as a control. The PCF was prepared by mixing all ingredients in a Kitchen Aid stand mixer to make a homogeneous paste. A 25-g sample of the mixture was cooked in the rapid visco analyzer (Perten RVA 4500, Macquarie Park, Australia) for 3 min at 95°C at 1,000 rpm for the first 2 min and 160 rpm for the last minute. The PCF was then transferred into molds and refrigerated till further analyses. The PCF was analyzed for moisture, pH, end apparent cooked viscosity, hardness, melted diameter, and melting temperature. The experiment was repeated 3 times using different batches of LP. The moisture of PCF ranged from 42.3% to 44.0% with a pH of 5.6 to 5.8. The end apparent cooked viscosity increased from 818.0 to 2,060.0 cP as the level of LP raised from 0.63% to 1.90%, whereas it was 660.0 cP in control. The hardness of PCF made with LP elevated from 61.9 to 110.1g as the level of LP increased; however, it was 85.6 g in control. The melted diameter decreased from 43 mm in control to 29 mm in 1.90% LP, while the melting temperature of PCF increased from 37.7°C in control to 59.0°C in 1.90% LP. We conclude that LP can be used as a substitute for DSP in PCF manufacture and has more capacity than DSP.

Sugar phosphorylation has many applications that can be used to develop dairy and food products. During the phosphorylation process, the color of the solution turns into a dark color. The dark color causes many challenges and limitations in using phosphorylation products. The dark color could cause unpleasant color changes in the products, so it is important to remove that color. Activated carbon has been utilized for decades to remove the dark color and improve the appearance of solutions such as sugar syrup and wastewater. This methodology is cheap and environmentally friendly. The objectives of this study were to develop a method to phosphorylate α-lactose monohydrate and milk permeate and to remove the dark color of solutions. The compositional characteristics of the solution, such as pH, total solids, and color parameters (L*—lightness; a*—redness; and b*—yellowness), were examined at different stages (seven stages) of washing the solutions. α-lactose monohydrate and MPP solutions were diluted with distilled water with a ratio of 1:2.2. Activated carbon was mixed with the solutions and left for 5 min at room temperature. Subsequently, the solutions were filtered. These steps were repeated seven times until there was a transparent (colorless) solutions. The experiment was repeated using three different batches of lactose and milk permeate solutions. Both solutions’ pH and total solids decreased with an increase in the number of washings with activated carbon. The International Commission on Illumination (CIE) L*a*b* scale was studied. The L* of the initial solutions was lower than that of the final solutions. However, the a* and b* of the initial solutions were higher than the final solutions. The total color difference (∆E) was calculated for both solutions. ∆E decreased with an increase in the number of washings with activated carbon in both solutions. We conclude that activated carbon can be used to remove the dark color that results from the phosphorylation process.

The aim of this research was to determine the effect of transglutaminase (TGase; 0, 0.3 and 3.0 units/g of protein) crosslinked micellar casein concentrate (MCC) and milk protein concentrate (MPC) on the functionality of process cheese product (PCP) loaf‐type formulation. The results showed that TGase significantly (P ≤ 0.05) increased viscosity after manufacture. Higher TGase levels also significantly (P ≤ 0.05) affected post‐manufacture melt characteristics such as melt viscosity and melt area measured using a rapid visco analyser and Schreiber melt test respectively. The study shows that the TGase treatment alters meltability of PCP.

Micellar casein concentrate (MCC) is a high protein ingredient that is typically produced using 3 stages of microfiltration with a 3x concentration factor and diafiltration. Acid curd is an acid protein concentrate, which can be obtained by precipitating the casein at pH 4.6 (isoelectric point) using starter cultures or di-rect acids without the use of rennet. Process cheese product (PCP) is a dairy food prepared by blending dairy ingredients with nondairy ingredients and then heating the mixture to get a product with an extended shelf-life. Emulsifying salts are critical for the desired functional characteristics of PCP because of their role in calcium sequestration and pH adjustment. The objectives of this study were to develop a process to produce a novel cultured micellar casein concentrate ingredient (cMCC; culture-based acid curd) and to produce PCP without emulsifying salts using different combinations of protein from cMCC and MCC in the formulations (2.0:1.0, 1.9:1.1, and 1.8:1.2). Skim milk was pasteurized at 76 degrees C for 16 s and then microfiltered in 3 microfiltration stages using graded permeability ceramic membranes to produce liquid MCC (11.15% total protein; TPr and 14.06% total solids; TS). Part of the liquid MCC was spray dried to produce MCC pow-der (75.77% TPr and 97.84% TS). The rest of the MCC was used to produce cMCC (86.9% TPr and 96.4% TS). Three PCP treatments were formulated with different ratios of cMCC: MCC, including 2.0:1.0, 1.9:1.1, and 1.8:1.2 on the protein basis. The composition of PCP was targeted to 19.0% protein, 45.0% moisture, 30.0% fat, and 2.4% salt. This trial was repeated 3 times using different batches of cMCC and MCC powders. All PCP were evaluated for their final functional properties. No significant differences were detected in the composition of PCP made with different ratios of cMCC and MCC except for the pH. The pH was expected to increase slightly with elevating the MCC amount in the PCP formulations. The end apparent viscosity was signifi-cantly higher in 2.0:1.0 formulation (4,305 cP) com-pared with 1.9:1.1 (2,408 cP) and 1.8:1.2 (2,499 cP). The hardness ranged from 407 to 512 g with no sig-nificant differences within the formulations. However, the melting temperature showed significant differences with 2.0:1.0 having the highest melting temperature (54.0 degrees C), whereas 1.9:1.1 and 1.8:1.2 showed 43.0 and 42.0 degrees C melting temperature, respectively. The melting diameter (38.8 to 43.9 mm) and melt area (1,183.9 to 1,538.6 mm2) did not show any differences in different PCP formulations. The PCP made with a 2.0:1.0 ratio of protein from cMCC and MCC showed better func-tional properties compared with other formulations.

Melt and stretch properties in dairy-based imitation mozzarella cheese (IMC) are affected by the amount of intact casein provided by dairy ingredients in the formulation. Rennet casein (RCN) is the preferred ingredient to provide intact casein in a formulation. Ingredients produced using membrane technology, such as milk protein concentrate (MPC) and micellar casein concentrate (MCC), are unable to provide the required functionality. However, the use of transglutaminase (TGase) has potential to modify the physical properties of MPC or MCC and may improve their functionality in IMC. The objective of this study was to determine the effect of TGase-treated MPC and MCC retentates on melt and stretch properties when they are used in IMC and to compare them with IMC made using RCN. The MCC and MPC retentates were produced using 3 different lots of pasteurized skim milk and treated with 3 levels of TGase enzyme: no TGase (control), low TGase: 0.3 units/g of protein, and high TGase: 3.0 units/g of protein. Each of the MCC and MPC treatments was heated to 72°C for 10 min to inactivate TGase and then spray dried. Each MCC, MPC, and RCN powder was then used in an IMC formulation that was standardized to 48% moisture, 21% fat, 20% protein, and 1% salt. The IMC were manufactured in a twin-screw cooker by blending, mixing, and heating various ingredients (4.0 kg). Due to extensive crosslinking, the IMC formulation with the highest TGase level (MCC or MPC) did not form an emulsion. The IMC made from MCC treatments had significantly higher stretchability on pizza compared with their respective MPC treatments. The IMC made from TGase-treated MCC and MPC had significantly lower melt area and significantly higher transition temperature (TT) and stretchability compared with their respective controls. Comparison of IMC made using TGase-treated MCC and MPC to the RCN IMC indicated no difference in TT or texture profile analysis-stretchability; however, the Schreiber melt test area was significantly lower. Our results demonstrated that TGase treatment modifies the melt and stretch characteristics of MCC and MPC in IMC applications, and TGase-treated MPC and MCC can be used to replace RCN in IMC formulations.

The amount of intact casein provided by dairy ingredients is a critical parameter in dairy-based imitation mozzarella cheese (IMC) formulation because it has a significant effect on unmelted textural parameters such as hardness. From a functionality perspective, rennet casein (RCN) is the preferred ingredient. Milk protein concentrate (MPC) and micellar casein concentrate (MCC) cannot provide the required functionality due to the higher steric stability of casein micelle. However, the use of transglutaminase (TGase) has the potential to modify the surface properties of MPC and MCC and may improve their functionality in IMC. The objective of this study was to determine the effect of TGase-treated MPC and MCC powders on the unmelted textural properties of IMC and compare them with IMC made using commercially available RCN. Additionally, we studied the degree of crosslinking by TGase in MPC and MCC retentates using capillary gel electrophoresis. Three lots of MCC and MPC retentate were produced from pasteurized skim milk via microfiltration and ultrafiltration, respectively, and randomly assigned to 1 of 3 treatments: no TGase (control); low TGase: 0.3 units/g of protein; and high TGase: 3.0 units/g of protein, followed by inactivation of enzyme (72°C for 10 min), and spray drying. Each MCC, MPC, and RCN was then used to formulate IMC that was standardized to 21% fat, 1% salt, 48% moisture, and 20% protein. The IMC were manufactured by blending, mixing, and heating ingredients (4.0 kg) in a twin-screw cooker. The capillary gel electrophoresis analysis showed extensive inter- and intramolecular crosslinking. The IMC formulation using the highest TGase level in MCC or MPC did not form an emulsion because of extensive crosslinking. In MPC with a high level of TGase, whey protein and casein crosslinking were observed. In contrast, crosslinking and hydrolysis of proteins were observed in MCC. The IMC made from MCC powder had significantly higher texture profile analysis hardness compared with the corresponding MPC powder. Further, many-to-one (multiple) comparisons using the Dunnett test showed no significant differences between IMC made using RCN and treatment powders in hardness. Our results demonstrated that TGase treatment causes crosslinking hydrolysis of MCC and MPC at higher TGase levels, and MPC and MCC have the potential to be used as ingredients in IMC applications.

This study aimed to examine the physicochemical properties of 30% calcium (Ca)-reduced micellar casein 80% protein powders (RC-MCC) and the functional properties of the resultant dispersions. The calcium reduction in the micellar casein (MCC) powder was achieved by subjecting the liquid micellular casein obtained from the microfiltration of pasteurized skim milk to carbon dioxide (CO₂) treatment before and during ultrafiltration. The CO₂ injection was controlled to obtain a 0 and 30% reduction in calcium in the C-MCC (control) and RC-MCC powders, respectively. The MCC powders were tested for physicochemical properties such as chemical composition, particle size distribution, and bulk density. The MCC powders were reconstituted in deionized water to test the functional properties of the dispersions, i.e., solubility, viscosity, heat stability, emulsifying capacity, emulsion stability, foam capacity, and foam stability. The CO₂ injection did not result in any significant differences in the composition except mineral contents, particularly calcium. The particle size and bulk density of RC-MCC powders were significantly (p < 0.05) lower than control powders. The RC-MCC powder dispersions showed increased heat stability compared to control, whereas no significant changes in viscosity and emulsification capacity were observed between the two dispersions. However, the emulsion stability and foam stability of RC-MCC dispersions were significantly lower than C-MCC dispersions. This study showed that by utilizing a novel microfiltration–CO₂ injection–ultrafiltration process, 30% calcium-reduced MCC powder was commercially feasible. This research also provides a detailed understanding of the effect of calcium reduction on the functional properties of resultant MCC dispersions. It showed that calcium reduction could improve the solubility of the powders and heat stability and foam capacity of the dispersions.