An approach to improve the baking properties and determine the onset of browning in fat-free mozzarella cheese.

Compared with low-moisture part-skim mozzarella and mozzarella cheese, bake performance of low-fat and fat-free mozzarella on pizza has a lot to desire. We hypothesized that a water-soaking pretreatment step of low-fat and fat-free cheese shreds before baking would improve pizza baking performance. The study also examined the correlation of the onset of cheese browning with the rate of moisture loss, changes in cheese surface temperature, and 3-dimensional (3D) plot L* a* b* CIELAB color analysis. The pretreatment of soaking cheese shreds in water improved the baking properties of fat-free mozzarella cheese on pizza. Compared with the control sample, which demonstrated significant shred identity, poor shred melt, fusion, and stretch during a pizza bake with fat-free mozzarella, the soaked cheese (SC) sample demonstrated satisfactory cheese melt, fusion, and stretch. In addition, the SC sample had desired browning as opposed to the control sample's excessive browning. The additional moisture from the soaking pretreatment aided in delaying the onset of cheese browning in the SC sample when compared with the control sample. For both the control and SC samples, there was a strong correlation between the onset of cheese browning with the peak of moisture-loss rate, and an increase in cheese surface temperature (>100°C). The color analysis of the 3D plot confirmed the relationship between the onset of cheese browning and the shift in L* (lightness), a* (red-green color), and b* (blue-yellow) values. According to the study's findings, soaking cheese shreds before baking can help improve bake performance on pizza. Furthermore, 3 measurement tools used in the study, (1) moisture-loss rate, (2) cheese surface temperature, and (3) 3D plot CIELAB color, were useful in determining the onset of cheese browning and can be applied to different intervention strategies to control cheese browning during pizza baking.

Use of micellar casein concentrate and milk protein concentrate treated with transglutaminase in imitation cheese products-Unmelted texture.

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.

Use of micellar casein concentrate and milk protein concentrate treated with transglutaminase in imitation cheese products-Melt and stretch properties.

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.

Short communication: Effect of pH on the heat stability of reconstituted reduced calcium milk protein concentrate dispersions.

This study aimed to investigate the heat stability of dispersions from reconstituted reduced-calcium milk protein concentrate (RCMPC) with 80% protein or more. The tested RCMPC powders were produced from skim milk subjected to CO2 treatment before and during the process of ultrafiltration. The CO2 injection was controlled to obtain 0 (control, no CO2 injection), 20, 30, and 40% reduction in calcium levels in the RCMPC powders. The RCMPC powders were reconstituted to 10% (wt/wt) protein in deionized water. These dispersions were tested for heat stability in a rocking oil bath at 140°C at unadjusted, 6.5, 6.7, 6.9, and 7.1 pH. Calcium ion activity (CIA) and ionic strength measurements were carried out using a Ca ion-selective electrode and conductivity meter. Unadjusted pH of the dispersions varied from 6.8 in control to 5.96 in 40% RCMPC dispersions. The CIA of unadjusted dispersions ranged from 1.31 mM in control to 2.83 mM in 40% RCMPC. Heat stability, expressed as heat coagulation time (HCT) of unadjusted dispersions decreased as the level of Ca removal in powders increased (from 13.81 min in control to 0.46 min in 40% RCMPC) and was negatively correlated with the CIA of the dispersions. For control RCMPC dispersions, the minimum and maximum heat stability were observed at dispersion pH of 6.5 and 6.9, respectively, followed by a decrease at pH 7.1 (CIA was the lowest). Dispersions from 40% RCMPC and pH 7.1 had the maximum HCT of 30.94 min among all RCMPC dispersions at all pH values. From this study, it can be concluded that improved heat stability in high protein formulation beverages subjected to UHT processing could be achieved through calcium reduction in milk protein concentrates using CO2 injection.

Adapting blood glucose meter biosensors for the measurement of lactose in dairy ingredients.

Commonly used lactose assays [enzymatic spectrophotometric absorbance (EZA) and HPLC] for dairy ingredients are relatively expensive and time consuming. A blood glucose meter (BGM)-based method has successfully been documented as a rapid lactose assay in milk. However, the BGM-based method has not been evaluated in dairy ingredients. The objective of this study was to evaluate the BGM-based lactose analysis method in whey-derived (WD) and skim milk-derived (SMD) ingredients. The study was carried out in 4 phases. In phase 1, the effect of pH and lactose concentrations on the BGM reading was investigated using a factorial design with 2 factors: pH (6.02-7.50) and lactose (0.2 or 0.4%). We found that BGM readings were significantly affected by lower pH values at both lactose levels. In phase 2, the effect of total solids and ingredient type was investigated using a factorial design with 2 factors: ingredient type (WD or SMD) and total solids (0-8%). It was observed that the BGM reading was significantly affected by ingredient type and total solids. Phase 3 involved developing a linear relationship between the BGM reading and the EZA reference method to ascertain the accuracy of the proposed BGM method. Different ingredient types (WD or SMD) and non-lactose solids (0.5-27%) model ingredient dilutions prepared over a range of lactose contents (0.08-0.62%) were measured using the BGM and EZA methods. The average absolute percentage bias difference between the BGM method and EZA reference method results for these model dilutions was found to be between 2.2 and 7.3%. In phase 4, 15 samples procured from commercial sources ranging from 0.01 to 81.9% lactose were evaluated using the BGM method and EZA reference method. The average absolute percentage bias difference for lactose results between the 2 methods ranged from 3.6 to 5.0% and 5.3 to 9.7% for well-performing and poorly performing meters, respectively. Overall, the BGM method is a promising tool for rapid and low-cost analysis of lactose in both high-lactose and low-lactose dairy ingredients.

The ability of spore formers to degrade milk proteins, fat, phospholipids, common stabilizers, and exopolysaccharides.

Spore formers are common spoilage-causing microorganisms in dairy products; however, their modes of spoilage (proteolysis, lipolysis, etc.) have not been described in detail for cultured dairy products such as sour cream and yogurt. The objective of the present study was to test the ability of spore-forming strains isolated from dairy environments for their spoilage-causing activities at typical sour cream (24°C) and yogurt (42°C) fermentation temperatures. A total of 25 spore-forming strains were isolated from different sources, including raw milk, pasteurizer balance tank, biofilms formed on heat exchangers, and milk powder. These strains were tested for proteolytic and lipolytic activities and for their ability to degrade phospholipids, common stabilizers (starch, gelatin, xanthan gum, pectin), and exopolysaccharides (EPS) at sour cream and yogurt fermentation temperatures. A higher percentage of positive strains was observed for selected activities at yogurt fermentation temperature compared with sour cream fermentation temperature. Identified proteolytic spore-forming strains, based on a skim milk agar method, were subsequently quantified for their level of proteolysis using non-casein nitrogen (NCN) content and sodium dodecyl sulfate-PAGE (SDS-PAGE). The proteolytic strains that showed the highest levels of proteolysis (highest percentages of NCN content) at 24°C were Bacillus mojavensis BC, Bacillus cereus DBC, Bacillus subtilis DBC, B. mojavensis DBC1, and Paenibacillus polymyxa DBC1. At 42°C the strains with the highest levels of proteolysis (highest percentages of NCN content) were B. subtilis DBC, B. mojavensis BC, B. mojavensis DBC1, B. cereus DBC, and Bacillus licheniformis DBC6. Results of SDS-PAGE demonstrated that proteolytic strains had primarily hydrolyzed ß- and κ-CN. A viscometric method was used to evaluate the susceptibility of exopolysaccharides (EPS) to degradation by selected spore formers. This method helped to determine that EPS produced by commercial yogurt and sour cream cultures is susceptible to degradation by spore formers present in dairy environments.

Selective extraction of phospholipids from whey protein phospholipid concentrate using supercritical carbon dioxide and ethanol as a co-solvent.

In recent years, using dairy phospholipids (PL) as functional ingredients has increased because PL have nutritional benefits and functional properties. In this study, a novel 2-step supercritical fluid extraction (SFE) process was used to extract whey protein phospholipid concentrate (WPPC), a dairy co-product obtained during the manufacture of whey protein isolate, for PL enrichment. In the first step, nonpolar lipids in WPPC were removed using neat supercritical carbon dioxide (S-CO2) at 41.4 MPa and 60°C. In the second stage, the feasibility of using the polar solvent ethanol as a co-solvent to increase the solubility of S-CO2 extraction solvent was explored. A 3 × 3 × 2 factorial design with extraction pressure (35.0, 41.4, and 55.0 MPa), temperature (40 and 60°C), and concentration of ethanol (10, 15, and 20%) as independent factors was used to evaluate the extraction efficiency providing the most total PL, and the best proportion of each individual PL from the spent solids collected during S-CO2 SFE. All lipid fractions were analyzed using thin-layer chromatography and high-performance lipid chromatography. The total amount of PL extracted from WPPC was significantly affected by ethanol concentration; the extraction pressure and temperature were nonsignificant. The optimal SFE condition for generating a concentrated PL lipid fraction was 35.0 MPa, 40°C, and 15% ethanol concentration; the highest amount of extracted PL averaged 26.26 g/100 g of fat. Moreover, adjusting SFE condition allowed successful recovery of a high concentration of sphingomyelin, phosphatidylcholine, and phosphatidylethanolamine, giving averages of 11.07, 10.07, and 7.2 g/100 g of fat, respectively, 2 to 3 times more than conventional solvent extraction. In addition, exhausted solids obtained after the SFE process were enriched with denatured proteins (72% on dry basis) with significantly more water-holding capacity and emulsifying capacity than untreated WPPC. Overall, this 2-stage SFE process using neat S-CO2 and ethanol has the greatest potential to produce a PL-rich lipid fraction from WPPC.

Influence of milk protein concentrates with modified calcium content on enteral dairy beverage formulations: Storage stability.

Control of calcium-mediated storage defects, such as age gelation and sedimentation, were evaluated in enteral high-protein dairy beverages during storage. To investigate the effects of reduced-calcium ingredients on storage stability, 2 batches each of milk protein concentrates (MPC) with 3 levels of calcium content were acquired [control, 20% calcium-reduced (MPC-20), and 30% calcium-reduced (MPC-30)]. Control and calcium-reduced MPC were used to formulate 8% (wt/wt) protein enteral dairy beverages. The formulation also consisted of other ingredients, such as gums, maltodextrin, potassium citrate, and sucrose. The pH-adjusted formulation was divided into 2 parts, one with 0.15% sodium hexametaphosphate (SHMP) and the other with 0% SHMP. The formulations were homogenized and retort sterilized at 121°C for 15 min. The retort-sterilized beverages were stored at room temperature for up to 90 d and particle size and apparent viscosity were measured on d 0, 7, 30, 60, and 90. Beverages formulated using control MPC with 0 and 0.15% SHMP exhibited sedimentation, causing a decrease in apparent viscosity by approximately 10 cP and clear phase separation by d 90. The MPC-20 beverages with 0% SHMP exhibited stable particle size and apparent viscosities during storage. In the presence of 0.15% SHMP, particle size increased rapidly by 40 nm on d 90, implying the start of progressive gelation. On the other hand, highest apparent viscosities leading to gelation were observed in MPC-30 beverages at both concentrations of SHMP studied. These results suggested that beverages formulated with MPC-20 and 0% SHMP would have better storage stability by maintaining lower apparent viscosities. Further reduction of calcium using MPC-30 resulted in rapid gelation of beverages during storage.

Influence of milk protein concentrates with modified calcium content on enteral dairy beverage formulations: Physicochemical properties.

Because of their high protein and low lactose content, milk protein concentrates (MPC) are typically used in the formulation of ready-to-drink beverages. Calcium-mediated aggregation of proteins during storage is one of the main reasons for loss of storage stability of these beverages. Control and calcium-reduced MPC [20% calcium-reduced (MPC-20) and 30% calcium-reduced (MPC-30)] were used to evaluate the physicochemical properties in this study. This study was conducted in 2 phases. In phase I, 8% protein solutions were prepared by reconstituting the 3 MPC and adjusting the pH to 7. These solutions were divided into 3 equal parts, 0, 0.15, or 0.25% sodium hexametaphosphate (SHMP) was added, and the solutions were homogenized. In phase II, enteral dairy beverage formulations containing MPC and a mixture of gums, maltodextrin, and sugar were evaluated following the same procedure used in phase I. In both phases, heat stability, apparent viscosity, and particle size were compared before and after heat treatment at 140°C for 15 s. In the absence of SHMP, MPC-20 and MPC-30 exhibited the highest heat coagulation time at 30.9 and 32.8 min, respectively, compared with the control (20.9 min). In phase II, without any addition of SHMP, MPC-20 exhibited the highest heat coagulation time of 9.3 min compared with 7.1 min for control and 6.2 min for MPC-30. An increase in apparent viscosity and a decrease in particle size of reconstituted MPC solutions in phases I and II with an increase in SHMP concentration was attributed to casein micelle dissociation caused by calcium chelation. This study highlights the potential for application of calcium-reduced MPC in dairy-based ready-to-drink and enteral nutrition beverage formulations to improve their heat stability.

Influence of partially demineralized milk proteins on rheological properties and microstructure of acid gels.

Innovative clean label processes employed in the manufacture of acid gels are targeted to modify the structure of proteins that contribute to rheological properties. In the present study, CO2-treated milk protein concentrate powder with 80% protein in dry matter (TMPC80) was mixed with nonfat dry milk (NDM) in different ratios for the manufacture of acid gels. Dispersions of NDM and TMPC80 that provided 100, 90, 70, and 40% of protein from NDM were reconstituted to 4.0% (wt/wt) protein and 12.0% (wt/wt) total solids. Dispersions were adjusted to pH 6.5, followed by heat treatment at 90°C for 10 min. Glucono-δ-lactone was added and samples were incubated at 30°C, reaching pH 4.5 ± 0.05 after 4 h of incubation. Glucono-δ-lactone levels were adjusted to compensate for the lower buffering capacity of samples with higher proportions of TMPC80, which is attributable to the depletion of buffering minerals from both the serum and micellar phase during preparation of TMPC80. Sodium dodecyl sulfate-PAGE analysis indicated a higher amount of caseins in the supernatant of unheated suspensions with increasing proportions of CO2-treated TMPC80, attributable to the partial disruption of casein micelles in TMPC80. Heat treatment reduced the level of whey proteins in the supernatant due to the heat-induced association of whey proteins with casein micelles, the extent of which was larger in samples containing more micellar casein (i.e., samples with a lower proportion of TMPC80). Particle size analysis showed only small differences between nonheated and heated dispersions. Gelation pH increased from ˜5.1 to ˜5.3, and the storage modulus of the gels at pH 4.5 increased from ˜300 to ˜420 Pa when the proportion of protein contributed by TMPC80 increased from 0 to 60%. Water-holding capacity also increased and gel porosity decreased with increasing proportion of protein contributed by TMPC80. The observed gel properties were in line with microstructural observations by confocal microscopy, wherein sample gels containing increasing levels of TMPC80 exhibited smaller, well-connected aggregates with uniform, homogeneous pore sizes. We concluded that TMPC80 can be used to partially replace NDM as a protein source to improve rheological and water-holding properties in acid gels. The resultant gels also exhibited decreased buffering, which can improve the productive capacity of yogurt manufacturing plants. Overall, the process can be leveraged to reduce the amount of hydrocolloids added to improve yogurt consistency and water-holding capacity, thus providing a path to meet consumer expectations of clean label products.

Influence of hydrodynamic cavitation on the rheological properties and microstructure of formulated Greek-style yogurts.

With limited applications of acid whey generated during the manufacture of Greek yogurts, an alternate processing technology to sidestep the dewheying process was developed. Milk protein concentrate (MPC) and carbon dioxide-treated milk protein concentrate (TMPC) were used as sources of protein to fortify skim milk to 9% (wt/wt) protein for the manufacture of Greek-style yogurts (GSY). The GSY bases were inoculated and fermented with frozen direct vat set yogurt culture to a pH of 4.6. Owing to the difference in buffering of MPC and TMPC, GSY with TMPC and MPC exhibited different acidification kinetics, with GSY containing TMPC having a lower fermentation time. The GSY with TMPC had a titratable acidity of 1.45% lactic acid and was comparable to acidity of commercial Greek yogurt (CGY). Hydrodynamic cavitation at 4 different rotor speeds (0, 15, 30, and 60 Hz) as a postfermentation tool reduced the consistency coefficient (K) of GSY containing TMPC from 79.4 Pa·sn at 0 Hz to 17.59 Pa·sn at 60 Hz. Similarly for GSY containing MPC, K values decreased from 165.74 Pa·sn at 0 Hz to 53.04 Pa·sn at 60 Hz. The apparent viscosity (η100) was 0.25 Pa·s for GSY containing TMPC and 0.66 Pa·s for GSY containing MPC at 60 Hz. The CGY had a η100 value of 0.74 Pa·s. Small amplitude rheological analysis performed on GSY indicated a loss of elastic modulus dependency on frequency caused by the breakdown of protein interactions with increasing cavitator rotor speeds. A steady decrease in hardness and adhesiveness values of GSY was observed with increasing cavitational intensities. Numbers of grains with a perimeter of >1mm of cavitated GSY with TMPC and MPC were 35 and 13 grains/g of yogurt, respectively, and were lower than 293 grains/g observed in CGY. The water-holding capacity of GSY was higher than that observed for a commercial strained Greek yogurt. The ability to scale up the process of hydrodynamic cavitation industrially, and the ease of controlling events of cavitation that can influence final textural properties of the product, make this technology promising for large-scale industrial application. Overall, the current set of experiments employed in the manufacture of GSY, which included the use of TMPC as a protein source in conjunction with hydrodynamic cavitation, could help achieve comparable titratable acidity values, rheological properties, and microstructure to that of a commercial strained Greek yogurt.

Textural performance of crosslinked or reduced-calcium milk protein ingredients in model high-protein nutrition bars.

Transglutaminase (Tgase) crosslinking and calcium reduction were investigated as ways to improve the texture and storage stability of high-protein nutrition (HPN) bars formulated with milk protein concentrate (MPC) and micellar casein concentrate (MCC). The MPC and MCC crosslinked at none, low, and high levels, and a reduced-calcium MPC (RCMPC) were each formulated into model HPN bars. Hardness, crumbliness, moisture content, pH, color, and water activity of the HPN bars were measured during accelerated storage. The HPN bars prepared with MPC were harder and more cohesive than those prepared with MCC. Higher levels of Tgase crosslinking improved HPN bar cohesiveness and decreased hardening during storage. The RCMPC produced softer, yet crumblier HPN bars. Small textural differences were observed for the HPN bars formulated with the transglutaminase crosslinked proteins or RCMPC when compared with their respective controls. However, modification only slightly improved protein ingredient ability to slow hardening while balancing cohesion and likely requires further improvement for increased applicability in soft-texture HPN bars.

Prediction of process cheese instrumental texture and melting characteristics using dielectric spectroscopy and chemometrics.

This study evaluated the potentiality of dielectric spectroscopy as a tool to predict the functional properties of process cheese. Dielectric properties of process cheese were collected over the frequency range 0.2 to 3.2GHz at 25°C. Dielectric spectra of process cheese were collected using a high-temperature, open-ended dielectric probe connected to a vector network analyzer. The present study was conducted using 2 sets of commercial process cheese formulations and a set of specially formulated process cheese. For the all the process cheese samples analyzed, a decrease in dielectric constant and dielectric loss factor was observed as the incident frequency increased. Partial least square regression (PLSR) and multilayer perceptron neural network models were developed using the dielectric spectra of process cheese to predict the hardness (gf), melting point (°C), and modified Schreiber melt diameter (mm) of process cheese. The prediction models were validated using the full cross-validation method. The ratio of prediction error to deviation was greater than 2 for melt diameter and hardness, indicating a good practical utility of the PLSR prediction models. The predictability of multilayer perceptron neural network was less than the PLSR models and could be due to the small number of training samples in the data sets. Dielectric spectroscopy coupled with PLSR could be a useful tool for the nondestructive measurement of functional properties of process cheese.

Solubilization of rehydrated frozen highly concentrated micellar casein for use in liquid food applications.

Highly concentrated micellar casein concentrate (HC-MCC), a potential ingredient of protein-fortified food, is a gel at cold temperature. It contains ~17 to 21% casein, with most serum proteins and lactose removed by microfiltration and diafiltration, and it is then further concentrated using vacuum evaporation. The HC-MCC can be stored frozen, and our objective was to determine the conditions needed to obtain complete solubility of thawed HC-MCC in water and to understand its gelation upon cooling. Dispersibility (ability to pass through a 250-µm mesh sieve), suspendability (percentage of protein not sedimented at 80 × g within 5min), and solubility (percentage of protein not sedimented at 20,000 × g within 5min) were measured at 4, 12, or 20°C after various mixing conditions. Gelation upon cooling from 50 to 5°C was monitored based on storage (G') and loss (G'') moduli. The gelled HC-MCC was also examined by transmission electron microscopy. Thawed HC-MCC was added to water to reach a protein concentration of 3% and mixed using high shear (7,500rpm) for 1min or low shear (800rpm) for 30min at 4, 12, 20, or 50°C and at pH 6.4 to 7.2. The HC-MCC completely dispersed at 50°C, or at ≤20°C followed by overnight storage at 4°C. Suspendability at 50°C was ~90% whereas mixing at ≤20°C followed by overnight storage resulted in only ~57% suspendability. Solubility followed a similar trend with ~83% at 50°C and only ~29% at ≤20°C. Mixing HC-MCC with 60mM trisodium citrate increased dispersibility to 99% and suspendability and solubility to 81% at 20°C. Cold-gelling temperature, defined as the temperature at which G'=G'' when cooling from 50 to 5°C, was positively correlated with protein level in HC-MCC. Gelation occurred at 38, 28, and 7°C with 23, 20, and 17% of protein, respectively. Gelation was reversible upon heating, although after a second cooling cycle the HC-MCC gel had lower G'. In micrographs of gelled HC-MCC, the casein micelles were observed to be within the normal size range but packed very closely together, with only ~20 to 50 nm of space between them. We proposed that cold-gelation of HC-MCC occurs when the kinetic energy of the casein micelles is sufficiently reduced to inhibit their mobility in relation to adjacent casein micelles. Understanding solubilization of rehydrated frozen HC-MCC and its rheological properties can help in designing process systems for using HC-MCC as a potential ingredient in liquid food.

Manufacture of modified milk protein concentrate utilizing injection of carbon dioxide.

Dried milk protein concentrate is produced from skim milk using a combination of processes such as ultrafiltration (UF), evaporation or nanofiltration, and spray drying. It is well established that dried milk protein concentrate (MPC) that contains 80% (MPC80) and greater protein content (relative to dry matter) can lose solubility during storage as a result of protein-protein interactions and formation of insoluble complexes. Previous studies have shown that partial replacement of calcium with sodium improves MPC80 functionality and prevents the loss in solubility during storage. Those studies have used pH adjustment with the addition of acids, addition of monovalent salts, or ion exchange treatment of UF retentate. The objective of this study was to use carbon dioxide to produce MPC80 with improved functionality. In this study, reduced-calcium MPC80 (RCMPC) was produced from skim milk that was subjected to injection of 2,200 ppm of CO2 before UF, along with additional CO2 injection at a flow rate of 1.5 to 2 L/min during UF. A control MPC80 (CtrlMPC) was also produced from the same lot of skim milk without injection of CO2. The above processes were replicated 3 times, using different lots of skim milk for each replication. All the UF retentates were spray dried using a pilot-scale dryer. Skim milk and UF retentates were tested for ζ-potential (net negative charge), particle size, and viscosity. All the MPC were stored at room (22±1°C) and elevated (40°C) temperatures for 6 mo. Solubility was measured by dissolving the dried MPC in water at 22°C and at 10°C (cold solubility). Injection of CO2 and the resultant solubilization of calcium phosphate had a significant effect on UF performance, resulting in 10 and 20% loss in initial and average flux, respectively. Processing of skim milk with injection of CO2 also resulted in higher irreversible fouling resistances. Compared with control, the reduced-calcium MPC had 28 and 34% less ash and calcium, respectively. Injection of CO2 resulted in a significant decrease in ζ-potential and a significant increase in the size of the casein micelle. Moreover, RCMPC had a significantly higher solubility after storage at room temperature and at elevated temperature. This study demonstrates that MPC80 with a reduced calcium and mineral content can be produced with injection of CO2 before and during UF of skim milk.

Effect of xylitol on the functional properties of low-fat process cheese.

Process cheese (PC) is a dairy food prepared by blending natural cheese, salt, emulsifying salts, and other dairy and nondairy ingredients, and heating with continuous agitation to produce a homogeneous product. Fat is a critical component of PC and plays an important role in its functional characteristics. The health concerns associated with fat consumption have led to an increase in the demand for low-fat dairy products. Reducing the fat content of PC results in poor functional properties such as increased hardness and reduced melt characteristics. The objective of the current study was to evaluate the effect of xylitol on the functional properties of low-fat PC. Three different low-fat PC formulations were prepared with 0% (control), 2%, and 4% xylitol. All 3 PC formulations were formulated to contain 5% fat, and each treatment was manufactured in triplicate. Rheological characteristics including elastic modulus, viscous modulus, and temperature at Tanδ = 1 (melt temperature) were determined using dynamic stress rheometry (DSR). The DSR was carried out at a frequency of 1.5 Hz and stress levels of 400 Pa, using a temperature sweep from 20 to 90 °C. The hardness of the samples was determined by using texture profile analysis (TPA). Compositional analysis indicated that all treatments had similar fat, protein, and moisture contents. Elastic and viscous moduli results obtained with DSR showed a significant difference between 0% xylitol (control) and xylitol-containing treatments in the temperature range of 30 to 80 °C. The melt temperature was not significantly different between the 3 treatments. However, TPA demonstrated that the addition of xylitol significantly decreased the hardness of low-fat PC. Based on TPA and DSR data obtained in this study, we determined that xylitol addition improved the functional properties of low-fat PC.

Effect of sodium gluconate on the solubility of calcium lactate.

Calcium and lactate are present in excess of their solubility in Cheddar cheese. Consequently, calcium lactate crystals (CLC) are a common defect in Cheddar cheese. A novel approach for preventing CLC is the addition of sodium gluconate. Sodium gluconate has the potential to increase the solubility of calcium and lactate by forming soluble complexes with calcium and lactate ions, and preventing them from being available for the formation of CLC. The objective of this study was to determine if sodium gluconate could increase the solubility of calcium lactate (CaL(2)). Seven CaL(2) solutions (5.31% wt/wt) with 7 levels of sodium gluconate (0, 0.5, 1, 1.5, 2, 3, and 4% wt/wt) were made in triplicate. Solutions were stored at 7 °C for 21 d, and were visually inspected for CLC formation. Subsequently, they were filtered to remove CLC and the supernatant was analyzed for lactic acid and gluconic acid by HPLC and for calcium by atomic absorption spectroscopy. The visual inspection demonstrated that CLC were formed in the solution with 0% gluconate after the first day of storage and CLC continued to accumulate over time. A minute amount of CLC was also visible in the solution with 0.5% gluconate after 21 d of storage, whereas CLC were not visible in the other solutions. The HPLC results indicated a higher concentration of calcium and lactic acid in the filtrate from the solutions containing added gluconate. Thus, sodium gluconate can increase the solubility of CaL(2).

Noncasein nitrogen analysis of ultrafiltration and microfiltration retentate.

Previous research has suggested that the standard noncasein nitrogen (NCN) measurement method for milk overestimates the NCN content of microfiltration (MF) retentate. The objective of this study was to develop a modified method to more accurately measure the NCN content of ultrafiltration and MF retentate products. The standard method is based on precipitation of casein micelles at their isoelectric point (4.6) with acetic acid. In the standard method, a 10-mL milk sample and 75 mL of 38°C water are placed in a 100-mL volumetric flask. One milliliter of 10% acetic acid solution is added and the flask is incubated at 38°C for 10 min. Subsequently, 1 mL of 1N sodium acetate solution is added and mixed. After cooling the contents to 20°C, the flask is made up to 100mL with water, mixed, and then filtered (Whatman No. 1 filter paper). The N content of the filtrate is then determined by Kjeldahl analysis and referred to as NCN. A method was developed that used a 50-mL centrifugal tube instead of a volumetric flask. This modification facilitated measurement of the pH after addition of acetic acid. Subsequently, the sample was centrifuged (800×g at 25°C) for 10 min to facilitate filtration with a smaller pore size filter paper (Whatman no. 6). In this study, we evaluated the effect of pH after addition of 1% acetic acid and pH of the final filtrate on NCN analysis. Four pH levels after acetic acid addition (4.0, 4.2, 4.4, and 4.6) and 2 pH levels after sodium acetate addition (4.6 and 4.8) were evaluated. As the pH after acetic acid addition was increased from 4.0 to 4.6, the NCN content significantly decreased. Sodium dodecyl sulfate PAGE results also indicated that the casein fractions present in the filtrate were significantly decreased when the pH was increased from 4.0 to 4.6. The NCN content slightly decreased but the difference was not significant when the final pH of the filtrate was increased from 4.6 to 4.8. Subsequently, the NCN contents of several ultrafiltration and MF samples were determined using the standard method and modified method. The modified method gave significantly lower NCN values for most samples as compared with the standard method.

Evaluation of commercially available, wide-pore ultrafiltration membranes for production of α-lactalbumin-enriched whey protein concentrate.

Commercially available, wide-pore ultrafiltration membranes were evaluated for production of α-lactalbumin (α-LA)-enriched whey protein concentrate (WPC). In this study microfiltration was used to produce a prepurified feed that was devoid of casein fines, lipid materials, and aggregated proteins. This prepurified feed was subsequently subjected to a wide-pore ultrafiltration process that produced an α-LA-enriched fraction in the permeate. We evaluated the performance of 3 membrane types and a range of transmembrane pressures. We determined that the optimal process used a polyvinylidene fluoride membrane (molecular weight cut-off of 50 kDa) operated at transmembrane pressure (TMP) of 207 kPa. This membrane type and operating pressure resulted in α-LA purity of 0.63, α-LA:ß-LG ratio of 1.41, α-LA yield of 21.27%, and overall flux of 49.46 L/m(2)·h. The manufacturing cost of the process for a hypothetical plant indicated that α-LA-enriched WPC 80 (i.e., with 80% protein) could be produced at $17.92/kg when the price of whey was considered as an input cost. This price came down to $16.46/kg when the price of whey was not considered as an input cost. The results of this study indicate that production of a commercially viable α-LA-enriched WPC is possible and the process developed can be used to meet worldwide demand for α-LA-enriched whey protein.

Development of a rapid method for the measurement of lactose in milk using a blood glucose biosensor.

Current methods for lactose measurement in dairy products are time consuming and tedious and may require expensive equipment and skilled technicians. The aim of this research was to develop a novel and rapid method for the routine measurement of lactose in dairy products. The proposed method is based on the rapid hydrolysis of lactose using ß-galactosidase and subsequently measuring glucose using a blood glucose meter. Blood glucose meters were developed after decades of research and clinical trials and are used extensively worldwide by individuals with diabetes to monitor their blood glucose levels. The method was developed and validated in a series of experiments. In the first experiment, temperature and time required for the near-complete hydrolysis of lactose were determined. Subsequently, the influence of glucose meters and their test strip lots were evaluated. We found that meters were not significantly different. However, the test strip lots were significantly different from each other. In the second experiment, the proposed method was validated using different concentrations of lactose solutions (1.9-6.5%) and compared with a HPLC-based reference method. In the third experiment, the proposed method was used to determine the lactose content of raw milk. The proposed method shows potential for rapid, routine, and low-cost measurement of lactose in milk and other dairy products.