乳化盐强化对乳蛋白浓缩物加工性质的影响

研究乳化盐强化对乳蛋白浓缩物85（MPC85）基本成分、粒径、溶解性和表面疏水性（H0）以及蛋白分子量的影响。结果表明,柠檬酸钠（SCS）单独使用或者与焦磷酸钠（SPP）复配均能够显著改变MPC85的粒径和溶解性,且缩短了达到稳定粒径和溶解性所需要的时间（p<0.05）。其中,单独使用SCS可使得MPC85粒径由31.37μm降低至20.67μm,达到稳定粒径值的时间缩短至360 min。SCS与SPS按照不同比例使用时,随着SCS占比的增加,粒径值显著降低（p<0.05）,且溶解性由77.42%增加至81.43%,同时达到稳定溶解度的时间缩短;乳化盐可以改变蛋白构象,使得更多疏水基团暴露,从而提高H0;复配乳化盐会降低分子量>60 ku的蛋白含量,且SPP和磷酸三钠（SPS）使得MPC85形成小分子量蛋白,分子量介于κ-CN与β-LG之间。      

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 emulsifying salts reduction on imitation cheese manufacture and functional properties

Imitation cheese (48%, 50% and 52% moisture) was manufactured using a Farinograph. The standard emulsifying salts (ES) concentration was 1.4%, giving a casein:ES ratio of 19:12. The effect of ES reduction on cheese manufacture and functionality, assessed by texture profile analysis, heat-induced flowability and dynamic rheology, was studied. Microstructure was investigated by light and cryo-scanning electron microscopy. Reducing ES increased processing time and hardness and decreased flowability and fat globule diameter. In comparison to standard ES, a reduction of up to 20% produced cheeses in reasonable processing times with slightly altered functionality. On further ES reduction, processing times greatly increased giving much harder and less meltable cheeses. Reducing ES by 40% increased processing times ∼3-fold, halved fat globule diameter and flowability and doubled hardness, compared to standard cheeses. At ES reduction above 40% the product obtained, after prolonged processing time, bore little resemblance to cheese.     

Effect of storage time and temperature of milk protein concentrate (MPC85) on the renneting properties of skim milk fortified with MPC85

This study investigated the effect of storage temperature (20–50 °C) and time (0–60 days) on the renneting properties of milk protein concentrate with 85% protein (MPC85). Reconstituted skim milk was fortified with the MPC85 (2.5% w/w) and the renneting properties of the skim milk/MPC85 systems were investigated using rheology. It was found that the final complex modulus (final G∗) and the yield stress of the rennet-induced skim milk/MPC85 gels decreased exponentially with storage time of the MPC85 for storage temperatures greater than 20 °C, with a greater effect at the higher storage temperatures. Changes in the solubility of MPC85 with storage time were correlated with the rheological properties. The primary phase of renneting (cleavage of κ-casein) was not affected by the storage of the MPC85; hence the effect was related to the secondary stage of renneting (aggregation/coagulation of rennet-treated casein micelles). Using a temperature–time superposition method, a master curve was formed from the final G∗, yield stress and solubility results. This suggested that the same physical processes affected the solubility and rennet gelation properties of the milks. It is proposed that the MPC85 protein in rennet-treated skim milk/MPC85 solutions may transform from an interacting material, when solubility is high, to an inert or weakly interacting material, when solubility is low, and that this results in the reduced final G∗ and yield stress of the rennet gels when MPC85 is stored at elevated temperatures for long periods.     

Effect of emulsifying salts containing potassium on the melting properties of block‐type dairy cheese analogue

Substituting sodium with potassium in emulsifying salts of pasteurized block‐type dairy cheese analogues was investigated. Rennet casein and butter were used as protein and fat sources for the manufacture of a product with 51% dry matter and 50% fat in dry matter. Different emulsifying salt blends contained sodium or potassium citrate and sodium polyphosphate. The cheese analogues were tested for their melting properties by oscillation rheometry and by empirical tests for meltability and fat release after 2 days, 4 and 12 weeks of cold storage. A recipe containing about 60% less sodium and a typical standard recipe without potassium showed very similar results during 4 weeks of cold storage.     

The effect of concentration and composition of ternary emulsifying salts on the textural properties of processed cheese spreads

We used regression analysis to model the influence of varying ratios of disodium hydrogenphosphate (DSP), tetrasodium diphosphate (TSPP) and sodium polyphosphate (POLY) upon the hardness, cohesiveness, and relative adhesiveness of processed cheese spread (dry matter – 40 g/100 g; fat in dry matter – 50 g/100 g) at total emulsifying salt levels of 2.0, 2.5 and 3.0 g/100 g. Specific ratios of DSP to TSPP that rapidly increased hardness and decreased cohesiveness (1:1–3:4) and relative adhesiveness (1:1–1:2) were identified. The effect of the specific ratio of DSP:TSPP on textural parameters of samples was weakening with the rising amount of POLY in the ternary mixture. With the amount of POLY above 60%, the effect of the specific ratio of DSP:TSPP on textural parameters of samples was insignificant. With an increasing concentration of emulsifying salts, the values of hardness and cohesiveness were rising while the values of relative adhesiveness of the processed cheeses were falling. However, neither the concentration of emulsifying salts nor the adjustment of pH of the samples reaching the optimal range (5.69–5.84) affected the general trend of dependence of the observed textural parameters of model processed cheeses on the changing proportion of DSP, TSPP and POLY (P ≥ 0.05).     

A proteomic approach to detect lactosylation and other chemical changes in stored milk protein concentrate

Milk proteins undergo chemical changes such as lactosylation, deamidation and protein cross-linking during processing and storage of milk products. A proteomic technique combining two-dimensional gel electrophoresis and mass spectrometry was used to investigate chemical modifications to proteins, in milk protein concentrate (MPC80), during storage. Lactosylation, deamidation and protein cross-linking were observed on 2-DE gels. They were storage temperature-, humidity- and time-dependent. Lactosylated whey proteins were well separated on 2-DE in vertical stacks of spots. The masses of the spots varied by multiples of 324, indicating the attachment of lactose to lysine residues in the proteins. The trypsin-digested spots of α-lactalbumin were analysed by MALDI-TOF mass spectrometry, which indicated multiple lactosylation sites. The lactose adducts on gels were quantified by image analysis, allowing development of adducts over time to be monitored. The results show that proteomics can be used for the detection and quantification of chemical modifications to proteins in stored MPC80.     

Effect of processing methods and protein content of the concentrate on the properties of milk protein concentrate with 80% protein

In recent years, a large increase in the production of milk protein concentrates (MPC) has occurred. However, compared with other types of milk powders, few studies exist on the effect of key processing parameters on powder properties. In particular, it is important to understand if key processing parameters contribute to the poor solubility observed during storage of high-protein MPC powders. Ultrafiltration (UF) and diafiltration (DF) are processing steps needed to reduce the lactose content of concentrates in the preparation of MPC with a protein content of 80% (MPC80). Evaporation is sometimes used to increase the TS content of concentrates before spray drying, and some indications exist that inclusion of this processing step may affect protein properties. In this study, MPC80 powders were manufactured by 2 types of concentration methods: membrane filtration with and without the inclusion of an evaporation step. Different concentration methods could affect the mineral content of MPC powders, as soluble salts can permeate the UF membrane, whereas no mineral loss occurs during evaporation, although a shift in calcium equilibrium toward insoluble forms may occur at high protein concentration levels. It is more desirable from an energy efficiency perspective to use higher total solids in concentrates before drying, but concerns exist about whether a higher protein content would negatively affect powder functionality. Thus, MPC80 powders were also manufactured from concentrates that had 3 different final protein concentrations (19, 21, and 23%; made from 1 UF retentate using batch recirculation evaporation, a similar concentration method). After manufacture, powders were stored for 6 mo at 30°C to help understand changes in MPC80 properties that might occur during shelf-life. Solubility and foaming properties were determined at various time points during high-temperature powder storage. Inclusion of an evaporation step, as a concentration method, resulted in MPC80 that had higher ash, total calcium, and bound calcium (of rehydrated powder) contents compared to concentration with only membrane filtration. Concentration method did not significantly affect the bulk (tapped) density, solubility, or foaming properties of the MPC powders. Powder produced from concentrate with 23% protein content exhibited a higher bulk density and powder particle size than powder produced from concentrate that had 19% protein. The solubility of MPC80 powder was not influenced by the protein content of the concentrate. The solubility of all powders significantly decreased during storage at 30°C. Higher protein concentrations in concentrates resulted in rehydrated powders that had higher viscosities (even when tested at a constant protein concentration). The protein content of the concentrate did not significantly affect foaming properties. Significant changes in the mineral content are used commercially to improve MPC80 solubility. However, although the concentration method did produce a small change in the total calcium content of experimental MPC80 samples, this modification was not sufficiently large enough (<7%) to influence powder solubility.     

Effects of standardization of whole milk with dry milk protein concentrate on the yield and ripening of reduced-fat cheddar cheese

Commercial milk protein concentrate (MPC) was used to standardize whole milk for reduced-fat Cheddar cheesemaking. Four replicate cheesemaking trials of three treatments (control, MPC1, and MPC2) were conducted. The control cheese (CC) was made from standardized milk (casein-to-fat ratio, C/F approximately 1.7) obtained by mixing skim milk and whole milk (WM); MPC1 and MPC2 cheeses were made from standardized milk (C/F approximately 1.8) obtained from mixing WM and MPC, except that commercial mesophilic starter was added at the rate of 1% to the CC and MPC1 and 2% to MPC2 vats. The addition of MPC doubled cheese yields and had insignificant effects on fat recoveries (approximately 94% in MPC1 and MPC2 vs. approximately 92% in CC) but increased significantly total solids recoveries (approximately 63% in CC vs. 63% in MPC1 and MPC2). Although minor differences were noted in the gross composition of the cheeses, both MPC1 and MPC2 cheeses had lower lactose contents (0.25 or 0.32%, respectively) than in CC (0.60%) 7 d post manufacture. Cheeses from all three treatments had approximately 10(9) cfu/g initial starter bacteria count. The nonstarter lactic acid bacteria (NSLAB) grew slowly in MPC1 and MPC2 cheeses during ripening compared to CC, and at the end of 6 mo of ripening, numbers of NSLAB in the CC were 1 to 2 log cycles higher than in MPC1 and MPC2 cheeses. Primary proteolysis, as noted by water-soluble N contents, was markedly slower in MPC1 and MPC2 cheeses compared to CC. The concentrations of total free amino acids were in decreasing order CC > MPC2 > MPC1 cheeses, suggesting slower secondary proteolysis in the MPC cheeses than in CC. Sensory analysis showed that MPC cheeses had lower brothy and bitter scores than CC. Increasing the amount of starter bacteria improved maturity in MPC cheese.     

Use of milk protein concentrate to standardize milk composition in Italian citric Mozzarella cheese making

To better exploit manufacturing facilities and standardize cheese quality, milk composition could be standardized by fortifying its protein content with a milk protein concentrate (MPC) addition so avoiding partially skimming the milk. With this aim Mozzarella cheese was obtained adding citric acid into milk standardized at 4% protein and a fat to protein ratio of 1.0. Protein fortification was obtained adding MPC produced by ultrafiltration. Milk, whey, curd, cheese and stretching water were weighed and analysed for total solid, fat and protein content, to measure component recovery and yield. Yield increase (from 13.8% to 16.7%) was due to the higher recovery of the milk total solids and proteins in MPC cheese (48.2 and 78.3%, respectively) and to the slightly higher cheese moisture, obtained with a little modification of the cheese technology when adding MPC. Milk fat in cheese was lower than that reported in literature. Hot water stretching of the curd resulted in very low losses (1%) of protein and considerable losses (14%) of fat for both control and MPC cheeses. The likely reasons of this low recovery are discussed and it can be supposed that a further cheese yield increase is possible by changing the curd stretching procedures.     

On quantifying the dissolution behaviour of milk protein concentrate

Milk protein concentrate (MPC) is a newly developed dairy powder with wide range of applications as ingredients in the food industry, such as cheese, yogurt, and beverage. MPC has relatively poor solubility as a result of their high protein content (40–90 wt%), with distinct dissolution behaviour in comparison to skim milk or whole milk powders. Here, a focused beam reflectance measurement (FBRM) was used to monitor the dissolution process of an MPC powder, with the data used to develop a kinetic dissolution model based on the Noyes–Whitney equation. The model was used to estimate the dissolution rate constant k and the final particle size in suspension d_∞, describing dynamic dissolution behaviours and final solubility respectively of a particular powder. In this work, the effects of dissolution temperature, storage duration and storage temperature on dissolution properties of an MPC powder were also investigated. A quantitative understanding of relationship between process and storage conditions with powder functionality could be achieved from k and d_∞ profiles. This approach can potentially be applied to predict the dissolution behaviour of specific dairy powders in a more robust manner than conventional solubility tests.     

Use of dry milk protein concentrate in pizza cheese manufactured by culture or direct acidification

Milk protein concentrate (MPC) contains high concentrations of casein and calcium and low concentrations of lactose. Enrichment of cheese milk with MPC should, therefore, enhance yields and improve quality. The objectives of this study were: 1) to compare pizza cheese made by culture acidification using standardized whole milk (WM) plus skim milk (SM) versus WM plus MPC; and 2) compare cheese made using WM + MPC by culture acidification to that made by direct acidification. The experimental design is as follows: vat 1 = WM + SM + culture (commercial thermophilic lactic acid bacteria), vat 2 = WM + MPC + culture, and vat 3 = WM + MPC + direct acid (2% citric acid). Each cheese milk was standardized to a protein-to-fat ratio of approximately 1.4. The experiment was repeated three times. Yield and composition of cheeses were determined by standard methods, whereas the proteolysis was assessed by urea polyacrylamide gel electrophoresis (PAGE) and water-soluble N contents. Meltability of the cheeses was determined during 1 mo of storage, in addition to pizza making. The addition of MPC improved the yields from 10.34 +/- 0.57% in vat 1 cheese to 14.50 +/- 0.84% and 16.65 +/- 2.23%, respectively, in vats 2 and 3 and cheeses. The percentage of fat and protein recoveries showed insignificant differences between the treatments, but TS recoveries were in the order, vat 2 > vat 3 > vat 1. Most of the compositional parameters were significantly affected by the different treatments. Vat 2 cheese had the highest calcium and lowest lactose contencentrations. Vat 3 cheese had the best meltability. Vat 1 cheese initially had better meltability than vat 2 cheese; however, the difference became insignificant after 28 d of storage at 4 degrees C. Vat 3 cheese had the softest texture and produced large-sized blisters when baked on pizza. The lowest and highest levels of proteolysis were found in vats 2 and 3 cheeses, respectively. The study demonstrates the use of MPC in pizza cheese manufacture with improved yield both by culture acidification as well as direct acidification.     

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.     

Casein hydration and fat emulsification during manufacture of imitation cheese, and effects of emulsifying salts reduction

The manufacture of imitation cheese in a Farinograph was interrupted at various times, and the casein matrix formed and the free liquid were collected and analysed. During manufacture, a torque profile was generated, which showed three distinctive stages; an initial torque peak “peak-1”, followed by a trough and finally a second “peak-2”. Analyses provided quantitative and qualitative evidence that the initial manufacturing stage (peak-1) was concerned with water uptake and the formation of a hydrated casein matrix, as ∼75% of the added water was absorbed. This was followed by a fat emulsification phase (trough) and, once sufficiently emulsified, by the incorporation of the fat to form a homogeneous cheese mass, at peak-2. A similar approach showed that the effect of emulsifying salts reduction was to retard casein hydration, reflected in an increase in peak-1 torque, and led to a prolonged mixing time to sufficiently emulsify fat and allow its incorporation.     

Manufacture of process cheese products without emulsifying salts using acid curd and micellar casein concentrate

Process cheese products (PCP) are dairy foods prepared by blending dairy ingredients (such as natural cheese, protein concentrates, butter, nonfat dry milk, whey powder, and permeate) with nondairy ingredients [such as sodium chloride, water, emulsifying salts (ES), color, and flavors] and then heating the mixture to obtain a homogeneous product with an extended shelf life. The ES, such as sodium citrate and disodium phosphate, are critical for the unique microstructure and functional properties of PCP because they improve the emulsification characteristics of casein by displacing the calcium phosphate complexes that are present in the insoluble calcium-paracaseinate-phosphate network in natural cheese. The objectives of this study were to determine the optimum protein content (3, 6, and 9% protein) in micellar casein concentrate (MCC) to produce acid curd and to manufacture PCP using a combination of acid curd cheese and MCC that would provide the desired improvement in the emulsification capacity of caseins without the use of ES. To produce acid curd, MCC was acidified using lactic acid to get a pH of 4.6. In the experimental formulation, the acid curd was blended with MCC to have a 2:1 ratio of protein from acid curd relative to MCC. The PCP was manufactured by blending all ingredients in a KitchenAid blender (Professional 5 Plus, KitchenAid) to produce a homogeneous paste. A 25-g sample of the paste was cooked in the rapid visco analyzer (RVA) for 3 min at 95°C at 1,000 rpm stirring speed during the first 2 min and 160 rpm for the last min. The cooked PCP was then transferred into molds and refrigerated until further analysis. This trial was repeated 3 times using different batches of acid curd. MCC with 9% protein resulted in acid curd with more adjusted yield. The end apparent viscosity (402.0–483.0 cP), hardness (354.0–384.0 g), melting temperature (48.0–51.0°C), and melting diameter (30.0–31.4 mm) of PCP made from different acid curds were slightly different from the characteristics of typical PCP produced with conventional ingredients and ES (576.6 cP end apparent viscosity, 119.0 g hardness, 59.8°C melting temperature, and 41.2 mm melting diameter) due to the differences in pH of final PCP (5.8 in ES PCP compared with 5.4 in no ES PCP). We concluded that acid curd can be produced from MCC with different protein content. Also, we found that PCP can be made with no ES when the formulation uses a 2:1 ratio of acid curd relative to MCC (on a protein basis).     

Kinetics of enthalpy relaxation of milk protein concentrate powder upon ageing and its effect on solubility

Kinetics of enthalpy relaxation of milk protein concentrate (MPC) powder upon short-term (up to 67 h) storage at 25 °C and a_w 0.85, and long-term (up to 48 days) storage at 25 °C and a range of a_w values (0–0.85) were studied by differential scanning calorimetry (DSC). The short-term study showed a rapid recovery of enthalpy for the first 48 h, followed by a slower steady increase with time. The non-exponential β parameter was calculated using the Kohlrausch–Williams–Watts function and found to be 0.39. Long-term storage showed that enthalpy relaxation depends on both storage period and water activity. The enthalpy value was much less for lower moisture content (mc) (a_w ? 0.23, mc ? 5.5%) than for higher mc (a_w ? 0.45, mc ? 8%) samples for a particular storage period. The results suggest that the presence of more water molecules, in close proximity to the protein surface facilitates kinetic unfreezing and subsequent motion of molecular segments of protein molecules towards thermodynamic equilibrium. Although de-ageing of stored samples did not reverse storage-induced solubility losses, the timescale of enthalpy relaxation was similar to that of solubility loss. It is suggested that enthalpy relaxation within stored samples allows structural rearrangements that are responsible for subsequent solubility decreases.     

Rheological properties of instant milk‐based puddings prepared with emulsifying salt‐containing milk powders

The present work analysed the rheological properties, water‐holding capacity (WHC) and syneresis of instant puddings prepared with the emulsifying salt‐containing milk powders (ESMPs), which contained different proportions of disodium phosphate (DSP) and tetrasodium pyrophosphate (TSPP). Rheological measurements revealed that increasing the proportion of TSPP in the ESMPs increased gel stiffness (indicated by high values of G?, G^* and consistency index) and WHC, and decreased the tan δ and syneresis of the instant puddings. It was concluded that different interactions can be assumed dependent on the proportion of DSP and TSPP in the ESMPs added to the pudding system, and a mechanism was proposed for observed changes.     

微波对醇法大豆浓缩蛋白乳化性的影响

为改善和提高醇法大豆浓缩蛋白的乳化功能特性,采用微波对醇法大豆浓缩蛋白进行改性,并以微波功率、改性时间、均质时间、pH、料液比、溶液质量、NaC l浓度及不同种类盐为改性影响因素,研究了其对改性蛋白乳化性的影响。结果表明,当蛋白浆液处理量为55 g,均质6 m in,微波功率640 W,改性时间1.5 m in,料液比1∶9(W/V),pH为9时,可使乳化能力达到96.9%。     

Yield and aging of Cheddar cheeses manufactured from milks with different milk serum protein contents

Whey proteins in general and specifically β-lactoglobulin, α-lactalbumin, and immunoglobulins have been thought to decrease proteolysis in cheeses manufactured from concentrated retentates from ultrafiltration. The proteins found in whey are called whey proteins and are called milk serum proteins (SP) when they are in milk. The experiment included 3 treatments; low milk SP (0.18%), control (0.52%), and high milk SP (0.63%), and was replicated 3 times. The standardized milk for cheese making of the low milk SP treatment contained more casein as a percentage of true protein and more calcium as a percentage of crude protein, whereas the nonprotein nitrogen and total calcium content was not different from the control and high SP treatments. The nonprotein nitrogen and total calcium content of the milks did not differ because of the process used to remove the milk SP from skim milk. The low milk SP milk contained less free fatty acids (FFA) than the control and high milk SP treatment; however, no differences in FFA content of the cheeses was detected. Approximately 40 to 45% of the FFA found in the milk before cheese making was lost into the whey during cheese making. Decreasing the milk SP content of milk by 65% and increasing the content by 21% did not significantly influence general Cheddar cheese composition. Higher fat recovery and cheese yield were detected in the low milk SP treatment cheeses. There was more proteolysis in the low milk SP cheese and this may be due to the lower concentration of undenatured β-lactoglobulin, α-lactalbumin, and other high molecular weight SP retained in the cheeses made from milk with low milk SP content.     

Chemical,textural, rheological,and sensorial properties of wheyless feta cheese as influenced by replacement of milk protein concentrate with pea protein isolate

Replacement of milk protein with protein isolates from vegetable resources can significantly influence the characteristics of feta whey less cheese and also decrease the cost of final production. In this study, various blends of milk protein concentrate (MPC) and pea protein isolate (PPI) were mixed at levels of 12% MPC and 0% PPI (MP0), 10% MPC and 2% PPI (MP2), 9% MPC and 3% PPI (MP3), 8% MPC and 4% PPI (MP4), 7% MPC and 5% PPI (MP5), 6% MPC and 6% PPI (MP6) and used in the manufacture of wheyless feta cheese. The chemical, textural, rheological, and sensorial properties, as well as the microstructure of the cheese samples, were evaluated after 1, 15, and 30 days of storage. The general linear model procedure of SAS statistical software was used for statistical analysis. Duncan's multiple range tests was used to compare the means of different treatments. The results showed that all properties of the cheeses were influenced by different levels of PPI due to different total solids content. The use of high concentrations of PPI resulted in a more open protein network, softer structure and decreasing the storage (G′) and loss (G″) moduli in the cheeses. Sensory evaluation of the samples revealed that total score in terms of flavor, texture and overall acceptability was gradually decreased with increasing PPI levels, but still preferable for the panelists. Furthermore, for each sample, with increasing levels of PPI, the whiteness and the greenness were decreased, but the yellowness was increased.