Delipidation of a whey protein concentrate by electroacidification with bipolar membranes

The separation of residual fats from whey protein concentrates (WPC) results in a better nutritional and functional utilization of this product. Bipolar membrane electroacidification (BMEA) technology allows acidification and demineralization of solutions without any salt addition. The principle of BMEA is based on proton formation from water molecule dissociation at the bipolar membrane interface. The objective of this work was to determine the effect of an electroacidification treatment at pH 4.5 on the precipitation of lipids. WPC electroacidification was carried out with or without preliminary demineralization by conventional electrodialysis. The effect of ionic strength on lipid precipitation rates was also evaluated by dilution of the WPC samples. Lipid precipitation levels of 35-39% were obtained using the electroacidification process without a dilution step, while the combination of BMEA and dilution of the WPC resulted in a decrease in lipid content by six-fold from 0.76 to 0.21%.     

Effect of conductivity control on the separation of whey proteins by bipolar membrane electroacidification

Since the limiting factor of the bipolar membrane electroacidification (BMEA) process at 20% WPI (whey protein isolate) was hypothesized to be the lack of mobile ion inherent to the protein solution at pH 5.0, the aim of the present work is to study the effect of the conductivity control on the precipitation behavior of whey protein. BMEA performances were evaluated by measuring electrodialytic parameters, protein kinetic precipitation, molecular profiles, and isolate chemical composition and purity. The highest protein precipitation with 10% WPI solution was obtained at pH 4.6 and at a conductivity level of 200 microS/cm maintained with many 0.4-mL additions of 1.0 M KCl (200 microS[+]), with a 46% precipitation of the total protein, beta-lg composing the main part of the precipitated protein. With a 20% WPI solution, it was possible to reach pH 4.65 with conductivity control at 350 microS/cm. However, the 27% protein precipitation was still low. The changes in viscosity as pH decreases observed at 20% WPI would decreased the final precipitation rate of beta-lg, since the viscosity of the 20% WPI dispersion was very different.     

Bipolar membrane electroacidification of demineralized skim milk.

The aim of this study was to evaluate the effect of decreasing the mineral content of skim milk by electrodialysis (ED) prior to electroacidification with bipolar membrane (BMEA) on the performance of the process, the chemical composition, and the physicochemical and functional properties of the isolates produced. ED used to demineralize the skim milk solution was very efficient. However, the electroacidification parameters were influenced by the demineralization level of the skim milk solution: the energy efficiency was decreased with an increase in demineralization, but it was still possible to perform BMEA at a very low conductivity level. Moreover, the isolates produced by BMEA after electrodialysis demineralization at different rates showed similar chemical composition, except on potassium and lactose contents for 75% demineralized isolate. These isolates, except on protein load for 75% demineralization rate, showed similar physicochemical and functional properties, whatever the demineralization rate.     

Solubilization of chitosan by bipolar membrane electroacidification

Chitosan, a partially deacetylated derivative of chitin, was solubilized by bipolar membrane electroacidification (BMEA). Bipolar/monopolar (anionic or cationic) configuration and chitosan addition mode (single step or stepwise) were examined. Chitosan solubility and electroacidification parameters were monitored during the process to determine the optimal conditions. Bipolar/anionic configuration and stepwise feeding mode led to chitosan solubilization yield of 91% in 60 min at 20 mA/cm(2). In this configuration, chitosan solution had a pH of 2.5, a conductivity of 8.5 mS/cm, and an ash content of 0.2%. Relative energy consumption was 0.05 kWh/L of 1% chitosan solution prepared. Although some chitosan particles were aggregated in the electrodialysis stack, limiting chitosan solubilization, BMEA allowed complete solubilization of chitosan circulating in the system.     

Bipolar membrane electroacidification to produce bovine milk casein isolate

Bipolar membrane electroacidification (BMEA) has been developed previously (Bazinet et al., Report for the Canadian Electricity Association 9326 U 987, 1996; Bazinet et al., J. Agric. Food Chem. 1997, 45, 2419-2425, 3788-3794) and has been used for isoelectric precipitation of soybean proteins. The purpose of this study was to validate the feasibility of BMEA for the precipitation of milk casein and to investigate the effect of flow rate. High-purity isolates containing 1.23 and 2.00% ash and 85.4 and 91.6% total protein were obtained with flow rates of 0.2 and 1.2 gal/min. The molecular composition profiles of the isolates obtained by HPLC showed that only caseins were precipitated. However, except for protein precipitation curves, the flow rate did not influence the final composition and purity of the isolates. These results showed that BMEA is a new alternative process for the production of high-purity bovine milk casein isolate.     

Effects of type of added salt and ionic strength on physicochemical and functional properties of casein isolates produced by electroacidification

A procedure developed for soybean protein precipitation which was based on electrodialysis was tested for the production of acid casein from reconstituted skim milk. In a previous paper, the performance of bipolar membrane electroacidification (BMEA) was evaluated under different conditions of ionic strength (micro(added) = 0, 0.25, 0.5, or 1.0 M) and added salt (CaCl(2), NaCl, or KCl) (1). The aim of this study, which is the complement of the work on evaluation of BMEA performance, was to evaluate the functionality of the protein isolates produced by BMEA and to compare the BMEA isolates to commercial isolates and an isolate produced by chemical acidification. It was not possible to show differences between the functional properties of isolates produced by BMEA, except at 1 M CaCl(2) micro(added), due to the variability of the isolates. However, the results showed that it is possible to obtain isolates similar to commercial isolates and that the addition of salt during the process does not induce variations in functional properties. From results on mineral concentrations, it appeared that the addition of monovalent cations did not influence the retention of monovalent or divalent cations in the BMEA isolates, while addition of divalent cations (CaCl(2)) influenced the retention of magnesium. According to previous results on evaluation of BMEA performances under different conditions of ionic strength and added salt, the difference observed for the BMEA isolate produced at 1.0 M CaCl(2) was confirmed.     

Effect of cationic membrane permselectivity on the efficiency of skim milk electroacidification

Bipolar membrane electroacidification (BMEA) uses the property of bipolar membranes to split water and the demineralization action of cation-exchange membranes (CEM). As milk mineral salt content is very sensitive to ionic strength and pH changes, the aim of this study was to better understand the effect of changes in mineral content during pH decrease and demineralization of skim milk. The objectives were to investigate the effect of different cationic permselective membranes (CSV and CMX membranes) on skim milk cation migration and protein precipitation during BMEA. The permselectivity of both membranes tested does not influence the final efficiency of BMEA. The purity of the bovine milk casein isolates produced was similar to or higher (97-98% versus 93.4-96.7) than those of commercial isolates, due to a reduced ash content (1.2 versus 2.0-3. 8%) resulting from the CEM demineralizing phenomenon. For both membranes, the main ionic species to migrate was the potassium ions.     

Straightforward process for removal of milk fat globule membranes and production of fat-free whey protein concentrate from cheese whey

A straightforward method for the separation of milk fat globule membrane (MFGM) and production of fat-free whey protein concentrate/isolate from cheese whey has been developed. Lowering of the conductivity of the whey from its initial value of about 5600 μS cm(-1) to about 2000-500 μS cm(-1) via diafiltration with water caused selective precipitation of MFGM when incubated for 30 min at pH 4.2 and 35 °C. The whey proteins remained soluble in the supernatant under these conditions. Experimental evidence suggested that precipitation of MFGM at pH 4.2 was not due to a nonspecific effect of lowering of the conductivity of the whey but due to the specific effect of removal of Ca2+ from the whey. The lipid content of whey protein isolate obtained by this process was <0.2%, and the protein loss was <14%. The method provides an industrially feasible process for the production of fat-free whey protein concentrate/isolate. The MFGM, which is reported to contain bioactive/nutraceutical lipids and proteins, is a valuable byproduct of the process.     

Production of soy protein concentrates using a combination of electroacidification and ultrafiltration

Soy protein concentrates produced by combining electroacidification and dead-end ultrafiltration with a membrane of 100 kDa (pH 7 and 6) were compared with concentrates produced by ultrafiltration (pH 9) and a traditional acid precipitation procedure at pH 4.5. Mineral removal during ultrafiltration (mainly potassium, phosphorus, and calcium) was enhanced for the pH 6 electroacidified extract, compared to the extract at pH 9. This yielded a concentrate with improved solubility characteristics. The solubility for the concentrate prepared at pH 6 was enhanced by as high as 45% when compared to the concentrate at pH 9. The concentrate produced according to the traditional acid precipitation process showed mineral contents and solubility profile similar to those of the pH 6 concentrate, but required twice as much water during the process. The effect of electroacidification treatments on ultrafiltration permeate flux was quantified through the measurement of the different hydraulic resistances. Cake resistance was the main resistance to the permeate flux, and it was minimum at pH 9, maximum at pH 7, and intermediate at pH 6.     

Mozzarella干酪加工过程中主要理化指标变化及其产率计算

该文目的在于为干酪功能特性、含水率和产率的控制提供理论依据，使用标准化原料乳经低温巴氏杀菌，采用无盐渍新工艺生产Mozzarella干酪，从添加发酵剂开始，到制成新鲜干酪，测定各阶段干酪凝块的温度、水分含量、pH值和滴定酸度及各阶段乳清和凝块的蛋白和脂肪含量，计算Mozzarella干酪的效能和产率。试验结果表明：在排乳清和粉碎加盐阶段，干酪凝块中的水分含量变化幅度最大，排出乳清中的蛋白和脂肪数量明显增加；干酪的脂肪回收率达到92.22%，实际测得的乳清中脂肪的损失率为7.62%；乳蛋白的回收率达到83.60%，仅有16.72%的蛋白质损失于乳清中；在堆酿阶段pH值有一个从6.3(干酪凝块5.5)至5.25的快速下降过程。Mozzarella干酪的实际产率达到12.38%，达到了同类型干酪的产率要求。Mozzarella干酪的理化指标达到了美国全脂Mozzarella干酪的标准。     

Milk excretion of ivermectin and moxidectin in dairy sheep: assessment of drug residues during cheese elaboration and ripening period

Ivermectin (IVM) and moxidectin (MXD) are broad-spectrum endectocide antiparasitic drugs extensively used in food-producing animals. The patterns of IVM and MXD excretion in milk were comparatively characterized following their subcutaneous administration (200 microg.kg(-1) of body weight) to lactating dairy sheep. The relationship between milk excretion and plasma disposition kinetics of both compounds was characterized. A pool of milk collected from all of the animals in each experimental group was used for cheese elaboration. IVM and MXD residual concentrations were assessed during the cheese-making process and ripening period. IVM and MXD concentrations were measured in plasma, milk, and milk product (whey, curd, and cheese) samples using an HPLC-based methodology with fluorescence detection. IVM and MXD were extensively distributed from the bloodstream to the mammary gland, and large quantities, particularly of MXD, were excreted in milk. Residual concentrations of both compounds were recovered in milk up to 30 (IVM) and 35 (MXD) days post-treatment. The total fraction of the administered dose excreted in milk for MXD was significantly higher than that of IVM. During cheese production, the highest residual concentrations of both molecules were measured in the curd. Thirty-four percent of the total drug residue measured in the pooled milk collected from treated sheep was lost during the cheese-making process. The lowest residual concentrations were measured in the whey. IVM and MXD concentrations in the elaborated cheese tended to increase during the ripening period, reaching the highest residual level at 40 days of cheese maturation. The long persistence of milk residual concentrations of MXD and IVM in lactating dairy sheep and the high concentrations found in cheese and other milk-related products should be seriously considered before recommendation of the extralabel use of these antiparasitic drugs in dairy animals.     

Volatile organic compounds in foods: a five year study

A purge and trap procedure was used with gas chromatography-mass spectrometry determination to analyze 70 foods for volatile organic compounds (VOCs). The results from analyses over a 5 year period (1996-2000) are reported. VOCs were found in at least one sample of all foods tested, although no single compound was found in each of the foods. The total amount of VOCs found in a single food item over the 5 year period ranged from 24 to 5328 ppb, with creamed corn (canned) the lowest and cheddar cheese the highest. Benzene was found in all foods except American cheese and vanilla ice cream. Benzene levels ranged from 1 to 190 ppb, with the highest level found in fully cooked ground beef. Benzene was found in 12 samples of cooked ground beef, with an average of 40 ppb. Benzene levels above 100 ppb were also seen in at least one sample each of a cola (138 ppb), raw bananas (132 ppb), and cole slaw (102 ppb). This compares to a maximum contaminant level of 5 ppb set by the U.S. EPA for drinking water.     

Direct enzyme-linked immunosorbent assay for determining aflatoxin M1 at picogram levels in dairy products

Protocols for detecting picogram quantities of aflatoxin M1 in dairy products were established. Milk samples were subjected to a reverse phase Sep-Pak C18 cartridge treatment before analysis by an enzyme-linked immunosorbent assay (ELISA) according to previously published procedures. M1 in yogurt, brick cheddar, and ripened Brie cheese was extracted by a modified Pons method, subjected to a normal phase silica cartridge treatment, and analyzed by ELISA. The detection limits for M1 in milk, yogurt, cheddar, and Brie were 10, 10, 50, and 25 ppt (ng/kg), respectively. Recovery for M1 added to these products was in the range 70-110%. Good agreement was found for M1 levels in several naturally contaminated milk samples analyzed by both ELISA and liquid chromatography.     

Impact of whey pH at drainage on the physicochemical, sensory, and functional properties of mozzarella cheese made from buffalo milk

In this study, the effects of whey pH at drainage on the physicochemical, sensory, and functional properties of mozzarella cheese made from buffalo milk during storage were investigated. Four cheese samples were manufactured using starter culture at different whey pH values [(A) 6.2, (B) 5.9, (C) 5.6, and (D) 5.3] and analyzed on the 1st, 28th, and 56th day. Ash, calcium, and phosphorus concentrations decreased as the whey pH at drainage was lowered. Cheese yield and calcium recovery were the highest in D cheeses. During storage, expressible serum levels decreased and nonexpressible serum levels increased, indicating an increase in the water holding capacity of the cheeses. Reducing the calcium content of cheeses increased meltability values, but an overly low calcium level (D cheeses) had an adverse effect on the meltability. The melting properties of cheese samples, except D cheeses, were improved with aging. A cheeses were the hardest and D cheeses the softest throughout storage. The 1st day sensory evaluations revealed that C and D cheeses were preferred and that A cheeses were not. All sensory properties of A cheeses were improved with storage. D cheeses were rated inferior to the others at the end of the storage time.     

Heat-induced aggregation of whey proteins: comparison of cheese WPC with acid WPC and relevance of mineral composition

Heat-induced aggregation of whey proteins in solutions made from two commercial whey protein concentrates (WPCs), one derived from mineral acid whey (acid WPC) and the other from cheese whey (cheese WPC), was studied using polyacrylamide gel electrophoresis (PAGE), size exclusion chromatography (SEC), and transmission electron microscopy (TEM). Heat treatment (75 degrees C) of acid WPC solutions (12.0%, w/w, pH 6.9) resulted in formation of relatively small "soluble" aggregates that were predominantly disulfide-linked. By contrast, heat treatment of the cheese WPC solutions (under the same conditions) caused formation of relatively large aggregates, containing high proportions of aggregates linked by noncovalent associations. The rate of aggregation of both beta-lactoglobulin and alpha-lactalbumin at 75 degrees C, measured as the loss of native proteins by PAGE, was higher in the cheese WPC solution than in the acid WPC solution. Cross dialysis of the two WPC solutions resulted in alteration of the mineral composition of each WPC solution and reversing their heat-induced aggregation behavior. The results demonstrated that the mineral composition is very important in controlling the aggregation behavior of WPC products.     

Analysis of free fatty acids in whey products by solid-phase microextraction

To evaluate the impact of Cheddar cheese starter cultures on the level of free fatty acids in liquid whey, a solid-phase microextraction (SPME) technique was utilized. The determination of response factors relative to an internal standard and the verification of linearity over a wide concentration range allowed for the quantitation of free fatty acids in experimentally produced liquid whey and in a wide range of dry whey ingredients. Results indicated that whey produced with a Lactococcus lactis subsp. lactis starter culture contained the highest level of total free fatty acids with significantly higher levels of lauric, myristic, and palmitic acids. Significant declines in oleic, linoleic, and palmitic acid occurred during storage. Commercial whey ingredients demonstrated a linear increase in free fatty acids with increasing percent protein, except for whey protein isolate, which had the lowest concentration. The use of SPME for the rapid analysis of free fatty acids in whey products should allow for further research to determine the importance of these compounds on the quality and stability of whey products.     

Lipolysis during ripening of Emmental cheese considering organization of fat and preferential localization of bacteria

This study followed the progression of lipolysis in Emmental cheese by quantifying the concentrations of individual free fatty acids (FFA) released during ripening in each of the different rooms: 12 days at 12 degrees C, 28 days at 21 degrees C, and 8 days at 4 degrees C. Lipolysis, which corresponded to 1.56% of fat, mainly occurred in the 21 and 4 degrees C rooms, with 68 and 16.5% of total FFA, respectively. The nonselectivity of lipolytic enzymes was evidenced: all fatty acids were released with level of > or =1%. Differential scanning calorimetry experiments showed that the thermal properties of cheese were affected by (i) lipolysis of fat, that is, the monoacylglycerols, diacylglycerols, and FFA that may be localized at the fat/whey interface, and/or by (ii) hydrolysis of high-melting-point triacylglycerols constituted mainly by long-chain saturated fatty acids (e.g., palmitic acid). Analysis of the cheese microstructure was performed using confocal laser scanning microscopy. Fat globules were mainly disrupted after pressing of curd grains, leading to the release of the milk fat globule membrane (MFGM); fat inclusions were surrounded by pockets of whey, delimited by casein strands. Moreover, colonies of bacteria were preferentially localized in situ at the fat/protein interface. This study showed that both the localization of bacteria and the supramolecular organization of fat which was not protected by the MFGM can help the accessibility of milk fat to lipolytic enzymes and then contribute to the quality of cheese.     

Aerobic biodegradation of precoagulated cheese whey wastewater

Prior to the application of an aerobic biological process, cheese whey wastewater has been pretreated by means of a precipitation stage by adding either NaOH or CaOH2. Both precipitating agents reduce roughly 50% of the raw wastewater chemical oxygen demand (COD). The sludge generated in the prestage shows acceptable settling properties, although solids from the CaOH2-treated effluent are better separated from the liquid bulk than those formed in NaOH-processed wastewater. In both situations, the presedimentation stage renders a supernatant more prone to biodegradation than the untreated effluent. The previous statement is corroborated by the determination of some biological kinetic parameters. Under the operating conditions used in this work, sludge generation after the biological process is reduced to a minimum. The sludge generated shows good settling properties, especially for those experiments in which CaOH2 has previously been added.     

Effect of different membrane separation technologies (Ultrafiltration and microfiltration) on the texture and microstructure of semihard low-fat cheeses

Semihard low-fat cheeses made from ultrafiltered (UF) or microfiltered (MF) milk were compared. The use of MF membranes and milder pasteurization of the milk reduced the retention of whey proteins in the retentate to 35%, compared with approximately 100% retained in the UF process. Microbiological development, physicochemical composition, and cheese ripening were not altered by the concentration processes. The lower retention of whey protein in MF cheeses accounted for their higher hardness, which correlated with higher firmness values in the textural analysis. Microstructure showed a protein matrix with open spaces through the protein network, although micrographs of UF cheeses showed the presence of spongy structures linked to the casein, which did not appear in MF cheeses and which correspond to the denatured whey protein bound to the casein. Firmness was scored better in MF cheeses, although when MF membranes were used, the optimum yields achieved using UF membranes were not attained.     

The addition of Propionibacterium freudenreichii to Raclette cheese induces biochemical changes and enhances flavor development

Two mixtures of Propionibacterium freudenreichii commercial strains were tested as adjunct cultures in pasteurized milk Raclette cheese to investigate the ability of propionibacteria (PAB) to enhance flavor development. Cheese flavor was assessed by a trained sensory panel, and levels of free amino acids, free fatty acids, and volatile compounds were determined. The PAB level showed a 1.4 log increase within the ripening period (12 weeks at 11 degrees C). Eye formation, which was not desired, was not observed in PAB cheeses. PAB fermented lactate to acetate and propionate and produced fatty acids by lipolysis, branched chain volatile compounds derived from isoleucine and leucine catabolism and some esters. One of the experimental cheeses received the highest scores for odor and flavor intensity and was characterized by higher frequencies of detection for some minor notes ("propionic"and "whey" odor, "sweet" taste). PAB can therefore be considered as potential adjunct cultures to enhance or modify cheese flavor development.