Milk Ultrafiltrate Research Articles

Effect of partial acidification on the ultrafiltration and diafiltration of skim milk: Physico-chemical properties of the resulting milk protein concentrates

This study investigates the effect of pre-acidification of skim milk between pH 6.7–5.4 on the physico-chemical properties of the resulting milk protein concentrate as well as the membrane performance. The membrane filtration process comprised ultrafiltration and 3 stages of diafiltration each with a volume concentration factor of 3. With increasing number of processing stages at a given pH, both the colloidal calcium and micellar caseins were gradually dissociated, while the micellar hydration increased and the micellar size decreased. With the increase in processing stages, casein micelles generally maintained their intact structure between pH 6.7–6.0, and then partially disintegrated into loosely entangled protein aggregates at pH 5.8–5.6, while complete micellar disruption occurred after extensive diafiltration at pH 5.4. Small-angle X-ray scattering indicated that the internal structure of the non-dissociated micelles became more homogenous when the number of processing stages increased and when the pre-acidification pH decreased.

The effect of emulsifying salts on the turbidity of a diluted milk system with varying pH and protein concentration

Solutions of 10 commonly used emulsifying salts (ES) listed in the Code of Federal Regulations (21CFR133.179) for pasteurized process cheese were tested for their effect on the turbidity of a diluted milk system at different pH and protein concentrations to characterize the conditions that affect micellar structure. Emulsifying salt solutions were made by mixing the ES in a 1-in-20 dilution of water in skim milk ultrafiltrate (3 kDa molecular weight cut-off) to obtain ES concentrations from 0 to 248 mM. Skim milk was added to solutions containing nanopure water, skim milk ultrafiltrate, and a specific ES ranging in concentration from 0 to 248 mM and pH 5, 5.8, 6.8, 7.8, and 8.8. The turbidity of the samples was measured as the optical density at 400 nm immediately after mixing (time, t = 0), after 30 s (t = 30s), and after 30 min (t = 30min). Emulsifying salts were found to cause a decrease in the turbidity of the system, which was modeled using an exponential decay model, where C* represents a threshold salt concentration at which rapid dissociation occurs. At pH values 5.8 and 6.8, the ES caused the greatest decrease in turbidity of the diluted milk system. At pH 5, the ES had the least effect on the turbidity of the system. Sodium hexametaphosphate was found to have the strongest dissociative effect, with a C* value of 0.33 mM for t = 0 at pH 6.8. In contrast, the largest C* value calculated at pH 6.8 was monosodium phosphate at 278.22 mM. Increased time resulted in lower C* values. The model established for this study can be used to predict the dissociation of casein micelles in the presence of various types of ES.

Fate of Escherichia coli and Kluyveromyces marxianus contaminants during storage of Greek-style yogurt produced by centrifugation or ultrafiltration

The production of Greek-style yogurts requires more processing steps than traditional yogurt, which increases the possibility of microbial contamination by pathogens or spoilage organisms. The growth and survival during storage of two microbial contaminants (Escherichia coli and Kluyveromyces marxianus) in Greek-style yogurt, produced by centrifugation or ultrafiltration, was compared with that in regular stirred yogurt. E. coli strain ATCC® BAA-1430™ was shown to be a suitable surrogate for pathogenic O157:H7 in yogurt. The increased buffering capacity of the Greek-style yogurts produced from ultrafiltered milk led to lower E. coli viability during storage. On the other hand, the Greek-style yogurt seems to promote faster growth of the dairy yeast K. marxianus at a storage temperature of 4 °C.

Physico-chemical, functional and rheological properties of milk protein concentrate 60 as affected by disodium phosphate addition, diafiltration and homogenization.

Ultrafiltration and diafiltration of skim milk altered delicate salt equilibrium and composition of 5× UF retentate (5× UFR), and thus adversely affected the reconstitutional and functional properties of milk protein concentrate (MPC) powders. It might be due to interaction and aggregation of proteins during spray drying. Therefore, this study was envisaged to investigate the effect of disodium phosphate (DSP) addition, diafiltration and homogenization of retentates on physico-chemical, functional and rheological properties of MPC60 powders. Solubility of fresh control powder was significantly lower than MPC60-H powder; at par with that of MPC60-DSP and MPC60-Na-K, but remained minimum after 60days of storage at 25±1°C. The pH (6.6) adjustment of 5× UFR with DSP, significantly enhanced the dispersability, wettability, specific surface area (SSA), heat coagulation time (HCT), emulsification capacity and stability; buffer index of MPC60-DSP powder over control. Diafiltration of 5× UFR with NaCl and KCl, significantly (P<0.05) decreased calcium content, but enhanced pH and mineral content of MPC60-Na-K powder. This treatment led to significant improvement in dispersability, SSA, emulsification capacity and stability, HCT and oil binding properties. Flowability, wettability, dispersability, HCT, foaming capacity, emulsification capacity and stability were also improved significantly in MPC60-H powder made from homogenized 5× UFR. Rheological behavior of reconstituted powder samples exhibited pseudoplastic behavior, best explained by Hershel Bulkley model. These MPC60 powders with improved functional properties can be used for the improvement of quality attributes of various food formulations.

RETRACTED: Enhancing the lipolysis of feta-type cheese made from ultrafiltered cow's milk

Abstract This study was conducted to investigate the effects of adding different levels of commercial pregastric lipase enzyme (calf lipase) on the free fatty acid profile of ultrafiltered Feta type cheese during ripening period. With an increase in added lipase level and ripening period, the main components of cheese including total solids, fat, fat in total solids, salt and salt in total solids did not change significantly but water soluble nitrogen increased. Increasing the added pregastric lipase level resulted in a significant decrease in the percentages of C 4:0 -C 8:0 free fatty acids while that of C 12:0 -C 18:0 and C 18:1 free fatty acids increased. According to sensory analysis of cheese samples, the best samples had the combination of 20, 40 and 60 days of ripening with 6 g/100 kg, 4 g/100 kg and 2 g/100 kg lipase in retentate, respectively. The addition of lipase to cheese milk could be recommended for the acceleration of flavor development and ripening of UF-Feta cheese over a short ripening period.

Milk ultrafiltrate analysis by ion chromatography and calcium activity for SMUF preparation for different scientific purposes and prediction of its supersaturation

In milk, the serum phase is in a dynamic equilibrium with insoluble salts within the casein micelle and therefore saturated with respect to calcium phosphate depending on pH, temperature and other compositional factors. In this study, simulated milk ultrafiltrate (SMUF) was therefore considered as a dynamic medium that approximates ultrafiltration (UF) permeates of a certain milieu condition resulting in changes in calcium and phosphate content as detected by ion chromatography. Due to reported spontaneous precipitation of existing SMUF solutions and interference with measurements and experiments, SMUF solutions were developed according to the chemical composition and physical parameters of UF permeate at different temperatures. SMUF solutions were proven to be as stable as their corresponding ultrafiltration permeates as they were similar in composition and calcium activity. Calcium activity was considered as a useful parameter to estimate the onset of supersaturation and spontaneous precipitation depending on calcium concentration and pH.

Concentration of Skim Milk by a Cascade Comprised of Ultrafiltration and Nanofiltration: Investigation of the Nanofiltration of Skim Milk Ultrafiltration Permeate

In order to reach a high volume reduction ratio (VRR) prior to drying of skim milk, a membrane cascade comprising of an ultrafiltration (UF) coupled with a nanofiltration (NF) can be applied. The present study investigated the impact of processing (filtration temperature, transmembrane pressure (TMP)) and product (feed pH) parameters on the NF of skim milk UF permeate. It could be shown that a low filtration temperature of 10 °C is more advantageous in terms of flux stability and rejection of the solute fraction as compared to higher filtration temperatures up to 45 °C. The solution pH did not affect permeate flux and lactose retention. However, in order to avoid calcium losses, it is more favorable to conduct the concentration at a pH of 6.8 instead of at a lower pH of 5. The application of a higher TMP (up to 4 MPa) enhances permeate flux and VRR as well as solute rejection during concentration of UF permeate. It was also shown that the retention of solutes decreases towards the end of the concentration process. As a consequence, the achievement of high final VRR must be weighed against increased product losses at the end.

Lipid droplets coated with milk fat globule membrane fragments: Microstructure and functional properties as a function of pH

Processed lipid droplets coated by milk fat globule membrane (MFGM) material are of primary interest to mimic the specific functions provided by the fat globules in milk and dairy products. The objectives were to investigate, as a function of pH, the properties and microstructure of MFGM-coated lipid droplets prepared with an ingredient rich in MFGM containing polar lipids and proteins. The samples were prepared in water and in milk ultrafiltrate. The combination of microscopy techniques, zeta potential and particle size measurements, and rheological determinations was used. We showed that all the components of the ingredient were highly sensitive to pH. Both the polar lipids and proteins contributed to the isoelectric point of the MFGM-rich ingredient at pI=4.2. Lipid droplets were coated with MFGM fragments both adsorbed at the surface of fat and protruding in the aqueous phase. Below pH5.5 the microstructure of the emulsions was affected by aggregation of the lipid droplets and formation of a gel. The emulsions prepared in water did not show coalescence upon 30days storage, while those prepared in milk ultrafiltrate showed coalescence for pH below 5.5. This study demonstrates that the MFGM-rich ingredient has excellent emulsifying properties and will contribute in the development of emulsions containing MFGM-coated lipid droplets for techno-functional, nutritional and health benefits (e.g. in infant formulas).

Rheological and thermogelling properties of commercials chitosan/β-glycerophosphate: Retention of hydrogel in water, milk and UF-milk

This study shows that how commercial chitosans owing three different molecular weights and high degree of acetylation can be neutralized closed to physiological pH using β-glycerophosphate to produce liquid solution at room temperature and formation of hydrogel upon subsequence heating up to the biological temperature (37 °C). The addition of β-glycerophosphate provided the precise buffering, controlled hydrophobic interaction and hydrogen bonding in order to retain chitosan in solution at 22 °C and neutral pH, and allowed gel formation upon heating up to 37 °C. Examination of flow and dynamic rheological properties, extrusion force and energy, heat induced gelation and gel stability of selected chitosan evidenced the flow performance and frequency dependent of elastic and viscous modules, extrusion ability, establishment of sol/gel diagram and retention of gel in three food mediums including water, pasteurized milk and ultrafiltered milk. It appeared that strength of gel network is governed by molecular weight and the higher molecular weight provided the superior gel strength. The study on retention of selected hydrogel in different mediums revealed that water has the most affinity to maintain the gel network.

Separation of milk fat globules via microfiltration: Effect of diafiltration media and opportunities for stream valorization.

Milk fat globule membranes (MFGM) sourced in buttermilk have gained recent interest given their nutritional value and functional properties. However, production of isolated MFGM has been challenging given their size similarity with casein micelles, which limits attempts toward fractionation by size exclusion techniques. Therefore, the hypothesis underpinning this study is that the removal of proteins from cream before butter-making facilitates MFGM isolation. As such, milk fat globules were separated from raw whole milk via microfiltration (1.4-µm pore diameter and 0.005-m2 filtration surface area) by using 3 diafiltration media; namely, skim milk ultrafiltration permeate, saline, and water. Their effects on the stability of the milk fat globules and protein permeation was elucidated. Whereas a substantial reduction in protein concentration was achieved with all diafiltration media (~90% reduction), water and saline produced negligible membrane fouling with better filtration performance. Moreover, diafiltration with skim milk ultrafiltration permeate exhibited reduced permeate flux. Colloidal stability of the resultant milk decreased with all diafiltration solutions due to changing composition and reduced apparent viscosity. Overall, microfiltration was found to be an efficient method for separation of milk fat globules from whole milk, leading to increased MFGM fragment concentration in buttermilk dry matter, thus making it more suitable for industrial utilization.

Effect of ultrafiltered milk permeate and non-dairy creamer powder concentration on low phenylalanine yoghurt's physicochemical properties during storage.

Phenylketonuria (PKU) is a genetic disorder that has no cure and all patients with this disorder must adhere to a special diet to prevent the onset of symptoms and mental retardation in children. In this study, analog yoghurt with good and acceptable nutrition benefit for PKU patients was produced. Accordingly, ultrafiltered milk permeate was added at two different concentrations of 4 and 5 w/w% and non-dairy creamer at two different concentrations of 1.5 and 2 w/w%. Subsequently, pH, acidity, protein, fat, dry matter, humidity, syneresis and Phe of the yogurts were determined. Protein content, dry matter, pH, acidity and Phe in the analog yogurt with 5% permeate and 2% non-dairy creamer were higher than other yoghurt samples, significantly (P<0.05). During the storage, pH and syneresis of samples reduced, while acidity significantly increased. Phe content of analog yoghurt was low (274mg/kg).

Simulation of membrane ultrafiltration of secondary raw milk

The results of a simulation of the ultrafiltration of secondary raw milk are discussed with the use of cottage cheese whey as an example. A mathematical model of ultrafiltration processes was developed with consideration for the formation of a concentration gel layer from lactoserum proteins on the membrane surface. The results of mathematical modeling were compared with the experimental data and conditions for the best fit to them we determined.

Effect of the consumption of β-lactoglobulin and epigallocatechin-3-gallate with or without calcium on glucose tolerance in C57BL/6 mice

Interactions between β-lactoglobulin (β-lg) and epigallocatechin-3-gallate (EGCG) may modulate their health benefits. The objective of this study was therefore to investigate the synergistic effect of consuming β-lg and EGCG complexes on glucose tolerance of C57BL/6 male mice given an oral glucose tolerance test (OGTT) and randomized to one of the following treatments administered prior to the OGTT: 1) simulated milk ultrafiltrate (SMUF-), 2) SMUF- + EGCG, 3) SMUF- + β-lg, 4) SMUF- + EGCG + β-lg, 5) SMUF + calcium (SMUF+) and 6) SMUF+ + EGCG + β-lg. We found no significant between-group difference in postprandial glucose response. However, when mice were separated in those who received β-lg from those who did not, we found that the latter displayed significantly higher postprandial glucose concentrations. Our results support the beneficial impact of β-lg on glycemic control and suggest that concomitant EGCG or calcium consumption does not improve this effect.

Calcium phosphate precipitation during concentration by vacuum evaporation of milk ultrafiltrate and microfiltrate

Vacuum evaporation is performed to concentrate milk constituents before their spray-drying. During this step, the mineral fraction and especially calcium phosphate precipitates. The aim of this study was to evaluate the mineral behavior with a special attention paid on calcium and inorganic phosphate during vacuum evaporation of milk ultrafiltrate (UF) and milk microfiltrate (MF)). Water evaporation was performed with a pilot-scale falling-film evaporator with a configuration close to those used in industry. Samples were analyzed for levels of water evaporation. Different approaches were used like i. analyses of mineral contents and their precipitation; ii. theoretical calculation of salt formed and ion distribution. During evaporation, formation of trouble with presence of particles was determined. In the same time, increases of all components present were determined with a precipitation of calcium phosphate. With UF, deposits of calcium phosphate in the evaporator were deduced whereas with MF, interaction of calcium phosphate with whey proteins limited the calcium phosphate precipitation. The mineral precipitates were always negatively charged. Moreover and due to evaporation, the increase in the ionic strength significantly decreased the negative charge present at the surface of calcium phosphate precipitates.

Effect of adjusted pH prior to ultrafiltration of skim milk on membrane performance and physical functionality of milk protein concentrate

Processing conditions during ultrafiltration of skim milk influence properties of the casein micelle and thereby the physical properties of milk protein concentrate (MPC). The aim of the study was to establish the effects of pH adjustment of skim milk feed to obtain MPC with desired emulsification properties. The ultrafiltration was conducted using commercially pasteurized skim milk with the pH adjusted to 6.7 (control), 6.3, 5.9, or 5.5 at 15°C until a volume concentration factor of 5 was reached. Effects of pH adjustment on selected physico-chemical properties (Ca content, particle size, ζ-potential) and functionalities (solubility, heat stability, emulsification capacity, and stability) of MPC were determined. Lowering the feed pH solubilized colloidal calcium phosphate that substantially contributed to modifying the properties of casein. This caused a reduction in the particle size while increasing the net negative charge. The structural modifications in proteins were manifested in the Fourier transform infrared spectra. Subsequent concentration did not induce any further protein structural changes. Such modifications to the casein micelles and colloidal calcium phosphate negatively affected the solubility and heat stability of the corresponding MPC powders. However, the emulsion activity index improved only until the pH of the feed was lowered to 5.9 and declined when pH was dropped to 5.5, followed with the loss of stability. Readjusting the pH of MPC powder dispersions to 6.7 restored their surface properties and thereby their functionality. Lowering the feed pH also negatively affected the membrane performance by clogging the membrane pores and lowering the flux, particularly at pH 5.5. Adjusting pH to 5.9 produced MPC with optimum emulsifying properties with minimal influence on membrane performance.

Acid gelation of whey protein microbeads of different sizes

In acidified dairy products, the size of the whey protein particles could play a key role in the final structure of the gel. In the present study, small (SM; 2.5 ± 1.2 μm), medium (MM; 4.2 ± 2.2 μm), and large (LM; 18.4 ± 7.2 μm) whey protein microbeads were produced by mixing a 150 g.kg−1 whey protein isolate (WPI) solution and n-dodecane in the presence of polyglycerolpolyricinoleate (PGPR) surfactant at different shear rates and were then stabilized through heat gelation. The microbeads were then washed by centrifugation, dispersed at 70 or 90 g.kg−1 in milk ultrafiltrate, and acidification was performed at 35 °C by adding glucono-δ-lactone to achieve the final pH of ~4.5 in 6 h. Acid gelation was monitored using small deformation rheology, while the gel microstructure was investigated microscopically. The results showed that smaller size of microbeads promoted gels with a higher stiffness and a smaller pore size distribution. The effects were particularly significant at SM microbeads as the number of particles in this system was higher than in LM or MM, hence more connectivity between particles.

Impact of calcium on the interactions between epigallocatechin-3-gallate and β-lactoglobulin

Milk proteins such as β-lactoglobulin (β-lg) have been shown to interact with epigallocatechin-3-gallate (EGCG), and possibly offset their degradation. However, currently no studies have taken into account other milk components such as calcium in the EGCG/β-lg interactions. The aim of this study was to characterize the interactions between EGCG and β-lg in a simulated milk ultrafiltrate (SMUF) with and without calcium. Different EGCG concentrations were tested in solutions containing β-lg and made in SMUF in the presence or absence of calcium. Particle size and zeta potential, as well as other measurements were performed on all solutions. Results showed an important increase in particle size and charge when β-lg was in the presence of EGCG. Particle charge grew significantly more negatively in the absence of calcium. It was demonstrated for the first time, to the best of our knowledge, that the presence of calcium greatly impacts the EGCG/β-lg interactions.

High concentration of skim milk proteins by ultrafiltration: Characterisation of a dynamic membrane system with a rotating membrane in comparison with a spiral wound membrane

The purpose of this work was to characterise the ultrafiltration of skim milk with a dynamic system with a rotating membrane regarding flux in milk protein concentration. The flux of the dynamic system showed a maximum at medium rotational speeds, probably due to the permeate backpressure or a shift in the deposited particle size range to smaller particles above a critical rotational speed. The flux increased almost linearly up to a transmembrane pressure (TMP) of 100 kPa. At higher TMP, the curves levelled off, especially at higher protein concentrations. The dynamic system was less limited by the increasing retentate viscosity and reached significantly higher volume reduction ratios (VRR) as compared with a spiral wound module (SWM). SWM are suitable to achieve VRR <5–6 before a dynamic system, possibly in combination with tubular ceramic membranes, could be used to achieve higher VRR >8.

Fouling control in ultrafiltration of bovine serum albumin and milk by the use of permanent magnetic field

Membrane separation processes are widely employed for protein concentration in the food industry. The major drawback is permeability reduction caused by concentration polarization and fouling. The present work evaluated the influence of a permanent magnetic field applied to the ultrafiltration process (UF) of protein solutions, as an alternative to improve the permeation performance and the permeability recovery. Permeation tests of bovine serum albumin (BSA) and milk as the feed protein solutions through a 50kDa hydrophilic polyethersulfone (PES) membrane were carried out in a tangential flow module. The feed pH was varied (4.0, 6.5 and 8.0) and ionic strength was modified by sodium chloride (NaCl). Permanent magnets were placed so as to obtain a maximum 0.7T magnetic field perpendicular to the membrane surface. The magnetic induction effect (MI) on the feed solutions was also studied by submitting the feed to the magnetic field for 2h before permeation run. The presence of magnetic field and the MI effect of the solution were effective in increasing both the permeate flux and the recovery of hydraulic permeability. The magnetic field application in the UF of protein solutions has proven to be an attractive alternative for improving process performance.

Comparison of the efficiency of different NF membranes for the enrichment of milk oligosaccharides from bovine milk

Oligosaccharides in milk (MOS) have been reported in the literature to exert various bioactivities and to modulate the immune system. However, processes to obtain milk oligosaccharides on industrial scale as food ingredients are currently not available. Therefore, the aim of the study on hand was the evaluation of different nanofiltration (NF) membranes for the enrichment of MOS from bovine milk. Moreover, a transfer of the NF process from laboratory to pilot plant and industrial scale was performed. The immunostimulatory effect of the MOS concentrates was studied by the activity of NFκB in human embryotic kidney cells (HEKnfκbRE-cells). NF was carried out with lactose hydrolyzed skimmed and ultrafiltered milk permeate by application of different membranes. The quantification of MOS was determined by high-pH anion-exchange chromatography with pulsed amperometric detection and parallel online electrospray ion trap mass spectrometry. The enrichment of MOS (3-sialyl-lactose, 6-sialyl-lactose, N-acetylgalactosaminyl-lactose) on laboratory, pilot plant and industrial scale was achieved by the retention of these oligosaccharides of at least 50 % in NF retentate. The content of MOS in relation to total sugar content in the retentate from NF on industrial scale was 100-fold higher than in the initial sample. The MOS retentates and the standards (3-sialyl-lactose, 6-sialyl-lactose) exhibited increased NFκB activity in HEKnfκbRE-cells. Although there exist a few studies about the enrichment of MOS by NF, this is the first report about a screening of the efficiency of different NF membranes for the enrichment of MOS on different technological scales of production.