A physicochemical investigation of membrane fouling in cold microfiltration of skim milk

The main challenge in microfiltration (MF) is membrane fouling, which leads to a significant decline in permeate flux and a change in membrane selectivity over time. This work aims to elucidate the mechanisms of membrane fouling in cold MF of skim milk by identifying and quantifying the proteins and minerals involved in external and internal membrane fouling. Microfiltration was conducted using a 1.4-μm ceramic membrane, at a temperature of 6 ± 1°C, cross-flow velocity of 6 m/s, and transmembrane pressure of 159 kPa, for 90 min. Internal and external foulants were extracted from a ceramic membrane both after a brief contact between the membrane and skim milk, to evaluate instantaneous adsorption of foulants, and after MF. Four foulant streams were collected: weakly attached external foulants, weakly attached internal foulants, strongly attached external foulants, and strongly attached internal foulants. Liquid chromatography coupled with tandem mass spectrometry analysis showed that all major milk proteins were present in all foulant streams. Proteins did appear to be the major cause of membrane fouling. Proteomics analysis of the foulants indicated elevated levels of serum proteins as compared with milk in the foulant fractions collected from the adsorption study. Caseins were preferentially introduced into the fouling layer during MF, when transmembrane pressure was applied, as confirmed both by proteomics and mineral analyses. The knowledge generated in this study advances the understanding of fouling mechanisms in cold MF of skim milk and can be used to identify solutions for minimizing membrane fouling and increasing the efficiency of milk MF.     

An economic assessment of proteins recovery from fish meal effluents by ultrafiltration

The main objective of this work was to assess the technical and economical feasibility of proteins recovery from fish meal effluents using crossflow membrane technology, namely, ultrafiltration (UF) and nanofiltration (NF).Mackerel processing effluents were pre-treated by microfiltration (MF cartridges battery of 80, 20 and 5 μm pore size) followed by UF (membrane Carbosep M2, 15 kDa MWCO) or NF (membrane Kerasep NanoN01A, 1 kDa MWCO). A suitable treatment for the fish meal effluents consisted of a MF pre-treatment followed by UF operating at 4 bar, 4 m/s, natural pH and ambient temperature. UF yielded an average permeation flux of 28 l/(m² h),¹ and 62% proteins rejection for a volume reduction factor of 2.3. Both membranes fully recovered their original permeabilities through an acidic/basic washing cycle. The economic assessment of proteins recovery from fish meal effluents by UF was accomplished for a production of 544 ton/yr of fish meal (66% protein content), yielding a net present worth of 160×10³ US$, interest rate of return of 17% and payback time of 8 years.     

The role of surface tension of re-used caustic soda on the cleaning efficiency in dairy plants

During the cleaning in place with recycled cleaning solutions, an increase of suspended solids (SS) and a decrease of the surface tension (γ) of caustic soda (NaOH) solutions were observed for various types of dairy equipment. The decrease of γ was shown to result from the chemical reactions of the milk protein and fat with the cleaning solutions. In this work, the respective roles of SS and γ on the cleaning efficiency, cleanliness and cleaning rate were determined. The cleaning test consisted of an ultrafiltration membrane fouled with skimmed milk and cleaned using four NaOH-based solutions: newly prepared NaOH (high γ), re-used NaOH (low γ) with and without pre-clarification and a newly prepared commercial detergent solution. In the range of γ (28.7–74.0 mJ m⁻²) and SS (0.0–1.7 g kg⁻¹) studied, the cleaning efficiency and the membrane hydraulic cleanliness were similar (0.91–0.94 and 0.69–0.71, respectively). However, it was found that solutions with a low γ resulted in a much faster cleaning rate. The presence of SS was mainly detrimental to the cleaning rate. For an efficient cleaning rate, high pH and low γ were important. A re-used NaOH solution with both low γ and SS was as fast as the commercial detergent solution at the same temperature (50 °C).     

Fractionation of pasteurized skim milk proteins by dynamic filtration

This paper describes a two-stage process for separating milk proteins from pasteurized skim milk in three fractions: casein micelles, β-Lactoglobulin (β-Lg) and other large whey proteins, and α-Lactalbumin (α-La). Casein micelles were extracted in the retentate of a microfiltration using rotating ceramic disk membranes. α-La and β-Lg transmissions remained between 0.8 and 0.98. Their yields in permeate reached 81% for α-La and 76.6% for β-Lg at a VRR of 5.4. The separation between β-Lg and α-La was carried out by UF using a rotating disk module equipped with a 50 kDa PES circular membrane. Permeate fluxes were very high, remaining above 340 L h^?1 m^?2 at VRR = 5 and 40 °C. α-La transmission remained generally between 0.2 and 0.13 giving yields from 28% to 34%. β-Lg rejection was above 0.94, giving a maximum selectivity of 4.2. These data confirm the potential of dynamic membrane filtration for separating α-La and β-Lg proteins from skim milk.     

Improvement of a sustainable hybrid technology for caseins isoelectric precipitation (electrodialysis with bipolar membrane/ultrafiltration) by mitigation of scaling on cation-exchange membrane

Electroacidification of milk by electrodialysis with bipolar membranes (EDBM) can be performed to produce isoelectric precipitated casein. In spite of advantages of EDBM, a problem of fouling hampers the industrial application of this technology. There are two types of fouling occurring during milk electroacidification such as protein fouling inside the EDBM stack and scaling on cation-exchange membrane (CEM). Recent studies demonstrated that protein fouling can be avoided by coupling an EDBM module with an ultrafiltration (UF) module. The present study aims the mitigation of scaling on the CEM. In order to attain this goal, two approaches were tested: 1) addition of KCl in the milk reservoir and 2) use of a UF membrane allowing higher permeate flux and consequently higher flow rates of solutions in the EDBM stack. Results of this study demonstrate the reasonableness of both approaches resulting in the significant decrease of CEM scaling (more than 30%).Industrial RelevanceCaseins are the major milk proteins largely produced in the world (around 330 000 t per year) and widely applied in the food and pharmaceuticals industries. There are several relevant features of proposed method (electrodialysis with bipolar membranes coupled with ultrafiltration (EDBM-UF)) for the casein production such as

• 1)absence of the hazardous reagents;
• 2)high purity of caseins due to the demineralization during EDBM;
• 3)no waste generation;
• 4)the base stream from EDBM module (co-product) can be used for the formation of caseinates.

The present work demonstrates the significant decrease of scaling on the cation-exchange membrane (more than 30%), which is the major problem of the EDBM-UF process. Indeed, during milk acidification, there is a liberation of minerals (Ca^2 + and Mg^2 +), which form the membrane deposit. This deposit negatively affects the process performance and leads to the membrane replacement. The cost of ion-exchange membranes in ED module comprises a major part of the total cost of EDBM-UF process. Thus, control and prevention of the membrane deposit will allow to increase a lifetime of ion-exchange membranes and to decrease a price of EDBM-UF treatment.     

Dead end ultra-filtration of sugar beet juice expressed from cold electrically pre-treated slices: Effect of membrane polymer on fouling mechanism and permeate quality

Purification of raw sugar beet juice expressed at ambient temperature (20 °C) from pretreated sugar beet slices by pulsed electric field (E = 600 V·cm^− 1, t_PEF = 10 ms, T = 20 °C) was studied on the laboratory scale by dead-end ultrafiltration tests. Polyethersulfone (PES) and Regenerated Cellulose (RC) membranes with the same nominal molecular weight cut-off of 30 kDa were used. Experiments were carried out in unstirred and stirred (at rotation speed of 500 rpm) mode at constant trans-membrane pressure of 2 bar. The effects of the membrane polymer (Polyethersulfone and Regenerate Cellulose) on the filtration flux and the permeate quality were studied. In order to identify the fouling mechanism, the filtration kinetics was modeled using combined fouling models. Results showed that the filtration productivity (filtration flux) and selectivity (rejection ratio of impurities) depended on the membrane polymer. The juice filterability was better with Regenerated Cellulose (RC) membrane while the polyethersulfone (PES) membrane ensured a better retention of impurities (colorants, proteins and colloids), leading to a higher juice purity. Experimental and models data adjustment showed that combined models were preferable to investigate the fouling mechanism for both unstirred and stirred filtration. The desirable sugar purity (95–96%) of filtrate implies the potential application of a novel process (PEF treatment-cold pressing-ultrafiltration) for sugar industrial production.Industrial relevancePre-treatment by pulsed electric field PEF allowed cold or mild extraction of sucrose from sugar beet roots. The combination of PEF and ultra-filtration allowed high yield sucrose extraction and purification with less energy consumption. Membrane fouling analysis led to better filtration producibility. The obtained data can be useful for optimization of the sucrose production with high yield in industrial extraction processes.     

Nanofiltration membrane fouling by oppositely charged macromolecules: investigation on flux behavior, foulant mass deposition, and solute rejection

Nanofiltration membrane fouling by oppositely charged polysaccharide (alginate) and protein (lysozyme) was systematically studied. It was found that membrane flux decline in the presence of both lysozyme and alginate was much more severe compared to that when there was only lysozyme or alginate in the feed solution. The flux performance for the mixed foulants was only weakly affected by solution pH and calcium concentration. These effects were likely due to the strong electrostatic attraction between the two oppositely charged foulants. Higher initial flux caused increased foulant deposition, more compact foulant layer, and more severe flux decline. The deposited foulant cake layer had a strong tendency to maintain a constant foulant composition that was independent of the membrane initial flux and only weakly dependent on the relative foulant concentration in feed solution. In contrast, solution chemistry (pH and [Ca2?]) had marked effect on the foulant layer composition, likely due to the resulting changes in the foulant-foulant interaction. The mixed alginate-lysozyme fouling could result in an initial enhancement in salt rejection. However, such initial enhancement was not observed when there was 1 mM calcium present in the feedwater, which may be attributed to the charge neutralization of the foulant layer.     

Concentration of Milk and Whey Using Composite,Spiral Wound,Reverse Osmosis Membranes

Two types of spiral wound, composite, reverse osmosis membranes, referred to as Phase I and Phase II, were studied in the concentration of milk and whey. The membranes can tolerate a pH range of 2 to 13, 50 ppm available Cl, 100 ppm H₂O₂, and temperatures up to 52°C.Two phase II membranes, Part A and Part B, sanitized using 50 ppm available Cl and 100 ppm H₂O₂, respectively, had average water fluxes of 71 an 69 L/m²h, respectively, at standard operating conditions. Phase II, Part A and Part B membranes had average NaCl rejections of 96.7 and 97.8%, respectively. Phase I modules had significantly lower permeate fluxes and salt rejections and significantly higher flux decline parameters than the Phase II membranes.The Phase II, Part B membranes had average permeate fluxes at a concentration factor of 2 for sweet whey, acid whey, and skim milk of 29, 36, and 14 L/m²h at standard operating conditions. The Phase II, Part B membranes had significantly higher average permeate fluxes than Phase II, Part A and Phase I membranes.Phase II membranes exhibited comparable or better performance than cellulose acetate membranes and can be used more easily in the dairy industry.     

Antioxidant activities of enzymatic rapeseed protein hydrolysates and the membrane ultrafiltration fractions

In this study, rapeseed protein isolate was hydrolyzed with various proteases to obtain hydrolysates that were separated by membrane ultrafiltration into four molecular size fractions (<1, 1–3, 3–5, and 5–10 kDa). Alcalase hydrolysis significantly (p < 0.05) produced the highest yield of protein hydrolysate while Flavourzyme produced the least. The <1 kDa fraction was the most abundant after the membrane ultrafiltration of the protein hydrolysates, which indicates that the proteases were efficient at reducing the native rapeseed proteins into low molecular weight peptides. Antioxidant properties of the resulting hydrolysates and membrane fractions were characterized and results showed the Pepsin + Pancreatin (P + P) protein hydrolysate had significantly highest (p < 0.05) scavenging activity against DPPH radical among the unfractionated enzymatic hydrolysates. But the P + P hydrolysate was not as effective as other hydrolysates during long-term inhibition of linoleic acid oxidation. For most of the samples, fractionation into the <1 kDa peptides significantly (p < 0.05) improved DPPH and superoxide scavenging properties when compared to the unfractionated protein hydrolysates. Only the <1 kDa fraction showed ferric reducing antioxidant power and the effect was dose-dependent. Overall, Alcalase and Proteinase K seem to be more efficient proteases to release antioxidant peptides from rapeseed proteins when compared to P + P, Flavourzyme and Thermolysin.     

Influence of enzymatic cross-linking on milk fat globules and emulsifying properties of milk proteins

The enzyme transglutaminase (TGase) can modify dairy protein functionality through cross-linking of proteins. This study examined the effects of TGase treatment on milk fat globules and the emulsifying properties of milk proteins. The extent of TGase-induced cross-linking of caseins increased with incubation time, with no differences between whole and skim milk. Extensive clustering of fat globules in extensively cross-linked raw whole milk occurred on homogenisation at 400 or 800 bar. Considerably less clustering of fat globules was observed when recombined milk (90 g fat L^–1) was prepared from TGase-treated skim milk and homogenised at 400 or 800 bar. TGase treatment did not affect fat globule size in cream, but prevented coalescence of fat globules therein, possibly through cross-linking of milk fat globule membrane components. TGase-induced cross-linking of milk proteins affected their emulsifying properties and may increase the stability of natural milk fat globules against coalescence.     

Available lysine,protein digestibility and lactulose in commercial infant formulas

Available lysine, in vitro protein digestibility and lactulose values were determined in 23 commercial infant formulas. The mean available lysine content of the formulas based on dairy proteins was 66.7±9.5 mg g⁻¹ protein, similar to that of human milk, while that of soy based formulas was considerably lower (45.0±8.3 mg g⁻¹ protein). In vitro protein digestibility values ranged 85.5–88.9% for soy-based formulas and 90.5–98.3% for formulas based on dairy proteins. Formulas based on milk enriched with whey had higher lactulose content than those based on cow's milk. However, all values were below the limit of 600 mg L⁻¹ recommended for UHT milk.     

Functional properties of milk proteins as affected by Maillard reaction induced oligomerisation

Milk proteins were modified by Maillard reaction with glucose, lactose, pectin and dextran and analysed for changes in molar mass distribution and functional properties. The study revealed that oligomeric (20,000–200,000 g/mol) and polymeric (>200,000 g/mol) Maillard reaction products with heterogeneous functional property profiles were generated. Compared to untreated milk proteins, milk protein/saccharide Maillard products formed highly viscous solutions and performed increased antioxidant capacity. Improved heat stability was detected for milk protein/dextran products, higher surface hydrophobicity for milk protein/glucose and milk protein/lactose products, and increased overrun for milk protein/pectin and milk protein/dextran products. Total milk protein/saccharide Maillard products formed outstandingly stable protein foams, Maillard products of total milk protein and glucose, lactose or pectin stable O/W-emulsions. Milk protein/pectin and milk protein/dextran Maillard products were characterized by increased emulsifying activity, and whey protein/saccharide products by enhanced pancreatic in vitro digestibility.The study characterizes Maillard reaction products of milk proteins and makes it possible to specifically select modified proteins for industrial applications according to the requirements towards food proteins, weighing changes in techno- and tropho-functional protein properties.     

Application of tailor-made membranes in a multi-stage process for the purification of sweeteners from Stevia rebaudiana

In this paper the performance of a three stage process with commercial as well as tailor-made polyethersulphone (PES) membranes for the purification of sweeteners from Stevia rebaudiana Bertoni was evaluated. Retentions of the sweeteners for a synthetic mixture and plant extract in combination with flux decline measurements indicated that, in contrast with the laboratory-made membranes, on most commercial membranes a foulant layer was formed that influenced the separation performance negatively. For the plant extract, the best commercial membrane (PW010) had a selectivity and flux similar to the best laboratory-made membrane (27% PES), but the laboratory-made membrane was preferred because it showed a slightly lower retention of the sweeteners, as desired. Starting from an extract purity of 11% with the overall process (microfiltration, ultrafiltration, nanofiltration) a purity of 37% and a yield of 30% could be reached.     

Formation of whey protein/κ-casein complexes in heated milk: Preferential reaction of whey protein with κ-casein in the casein micelles

Studies of the formation of soluble κ-casein/whey protein (WP) complexes in heated (90 °C 10 min⁻¹) milk and related mixtures of proteins have been made. The use of milk samples containing different genetic variants, and having different compositions, allowed the effects of changing the natural protein balance on the formation of particles to be investigated. In addition, studies were made of the effects of addition of WP or of purified κ-casein to the milk samples. The addition of WP caused an increase in the amount and the size of the complexes, but addition of κ-casein to the milk had little or no effect on the complex formation, nor did it seem that the added κ-casein could react with the WP in the milk. Conversely, in systems where the casein micelles were absent, the purified κ-casein reacted well with WP, suggesting that in milk heated at its normal pH the WP react preferentially with the κ-casein on the casein micelles.     

Baroprotection of vegetative bacteria by milk constituents: A study of Listeria innocua

The baroprotective effect of milk constituents on Listeria innocua 4202 treated at 350 or 500 MPa for 5 min was examined. High-pressure (HP) treatment of L. innocua 4202 (1×10⁹ cfu mL⁻¹) resulted in complete inactivation in simulated milk ultra-filtrate (SMUF), a ∼5.0 log reduction in phosphate-buffered saline and a ∼2.9 log reduction in milk. The addition of micellar casein to SMUF increased survival of the bacterium by 3 logs, compared with SMUF alone, but the protective effect was negated if the minerals associated with the casein micelles were removed. The colloidal minerals calcium (30 mm), magnesium (5 mm), citrate (10 mm) and phosphate (20 mm), suspended in SMUF increased survival by ∼3.3, ∼1.7, ∼3.3 and ∼3.5 logs, respectively. The buffering capacity of the suspending medium was found to be a key factor in microbial baroresistance. Buffering by phosphate and citrate in milk may protect microorganisms against changes in pH during HP treatment, whereas the divalent cations calcium and magnesium may protect cell membranes against HP.     

Ultrafiltration flux of acid whey obtained by lactic acid fermentation

Acid whey was prepared from reconstituted ultra-low heat skimmed milk powder fermented with Lactobacillus helveticus, clarified by centrifugation, pH adjusted and ultrafiltered (cut-off limit 10 or 30 kDa) at 50 °C to a volume reduction ratio of 10. Centrifugation primarily removed the serum albumin and, to a lesser extent, immunoglobulins, considered the most critical membrane foulants during ultrafiltration of acid whey. Below pH 3.9 the flux improvement was directly dependent on pH lowering. At pH 3.9 a deviation point in the relationship between pH and flux of acid whey was observed. Above this pH a severe flux decline was detected and at pH 4.6 the fermented acid whey was non-filterable. Largest flux increase was obtained at a transmembrane pressure of 2.0 bar and 50 °C. Under these conditions the permeation flux achieved using a 30 kDa membrane was about 34 ± 5 kg h⁻¹m⁻², comparable with that for sweet whey.     

Milk enhances intestinal absorption of green tea catechins in in vitro digestion/Caco-2 cells model

The effect of milk on the absorption of polyphenols is still controversial so far. In order to determine the impact of milk addition on green tea catechins bioaccessibility and intestinal absorption an in vitro digestion/Caco-2 cell model was applied. Green tea extract (GTE) was solubilized in distilled water at 23 °C and 100 °C, combined with skimmed milk (GTE + 10% milk and GTE + 25% milk) and subjected to simulated gastric and intestinal digestion, followed by transepithelial absorption in Caco-2 cells monolayers. In the mixture with milk, gallated catechins: ECG and EGCG showed binding to milk proteins while EC and EGC seemed to have weaker affinity. Catechins were stable during gastric incubation and very sensitive to intestinal digestion. Bioaccessibility of green tea catechins brewed at 100 °C was higher than brewed at 23 °C. Catechins from digested GTE with 10% and 25% milk exhibited enhanced intestinal permeability in Caco-2 model in comparison to non-digested GTE and digested GTE without milk. Apparent permeability coefficients (P_app) of EGCG and ECG in digested GTE with 25% milk were significantly higher compared to those in GTE with 10% milk, and amounted to 2.41 × 10^− 6 cm/s and 1.39 × 10^− 6 cm/s. The recoveries of all catechins in GTE with milk in Caco-2 cells after 2 h incubation were significantly higher than that without milk. To summarize, these data suggest that milk addition may increase catechin bioavailability by enhancing their transepithelial absorption and uptake from green tea extract.     

Antihypertensive activity of milk fermented by Enterococcus faecalis strains isolated from raw milk

A total of 231 microorganisms were isolated from raw cow milk samples and the angiotensin-converting enzyme-inhibitory (ACEI) activity of the resultant fermented milk produced with the isolated microorganisms was assayed. Forty-six of these microorganisms were selected on the basis of high ACEI activity. Four Enterococcus faecalis strains stood out as producers of fermented milk with potent ACEI activity (IC₅₀ (the protein concentration that inhibits 50% of ACE activity): 34–59 μg mL⁻¹). Single doses (5 mL kg⁻¹) of the whey fraction obtained from these fermented milk samples were administered to spontaneously hypertensive rats (SHR) and to normotensive Wistar-Kyoto (WKY) rats in order to investigate their possible antihypertensive activity. Highly significant decreases in the systolic blood pressure (SBP) and in the diastolic blood pressure (DBP) were observed when the fermented milk was administered to SHR. Nevertheless, the fermented milk did not modify the SBP and the DBP of the WKY rats. Raw cow milk is an excellent source of wild lactic acid bacteria able to produce fermented milk with antihypertensive activity and antihypertensive activity of milk fermented by Enterococcus faecalis strains was associated with peptides different from Ile-Pro-Pro and Val-Pro-Pro.     

Development of a fermented goat's milk containing probiotic bacteria

A set-type fermented milk manufactured from goat's milk was developed. Optimal curd tension was achieved by supplementation of milk with skim milk powder and whey protein concentrate (WPC). Milk was fermented employing a commercial probiotic starter culture (ABT-2), which contained Streptococcus thermophilus ST-20Y, Lactobacillus acidophilus LA-5, and Bifidobacterium BB-12. Supplementation of milk with 3% WPC reduced fermentation time by 2 h due to the increase in viable counts of S. thermophilus and Bifidobacterium by 0.3 and 0.7 log units, respectively. Addition of WPC increased the protein content (1%) as well as potassium and magnesium content (0.3 and 0.02 g kg⁻¹, respectively). Increase of the protein content led to an increase in the apparent viscosity and gel firmness of the product, and at the same time whey syneresis was reduced. As a consequence, the product received a high score for appearance, taste, aroma, texture and overall acceptance.     

Fouling of nanofiltration, reverse osmosis, and ultrafiltration membranes by protein mixtures: the role of inter-foulant-species interaction

Protein fouling of nanofiltration (NF), reverse osmosis (RO), and ultrafiltration (UF) membranes by bovine serum albumin (BSA), lysozyme (LYS), and their mixture was investigated under cross-flow conditions. The effect of solution chemistry, membrane properties, and permeate flux level was systematically studied. When the solution pH was within the isoelectric points (IEPs) of the two proteins (i.e., pH 4.7-10.4), the mixed protein system experienced more severe flux decline compared to the respective single protein systems, which may be attributed to the electrostatic attraction between the negatively charged BSA and positively charged LYS molecules. Unlike a typical single protein system, membrane fouling by BSA-LYS mixture was only weakly dependent on solution pH within this pH range, and increased ionic strength was found to enhance the membrane flux as a result of the suppressed BSA-LYS electrostatic attraction. Membrane fouling was likely controlled by foulant-fouled-membrane interaction under severe fouling conditions (elevated flux level and unfavorable solution chemistry that promotes fouling), whereas it was likely dominated by foulant-clean-membrane interaction under mild fouling conditions. Compared to nonporous NF and RO membranes, the porous UF membrane was more susceptible to dramatic flux decline due to the increased risk of membrane pore plugging. This study reveals that membrane fouling by mixed macromolecules may behave very differently from that by typical single foulant system, especially when the inter-foulant-species interaction dominates over the intra-species interaction in the mixed foulant system.