Effects of Adding Low Levels of a Disulfide Reducing Agent on the Disulfide Interactions of β-Lactoglobulin and κ-Casein in Skim Milk

Effects of pore diameters (100, 50, and 20 nm), concentration factors (1–8) and processing stages (1–5) on the transmission of major serum proteins (β-lactoglobulin and α-lactalbumin) and minor serum proteins (immunoglobulin (Ig) G, IgA, IgM, lactoferrin (LF), lactoperoxidase (LPO), xanthine oxidase (XO)) during ceramic microfiltration (MF) of skim milk were studied. Holstein skim milk was microfiltered at a temperature of 50 °C, a transmembrane pressure of 110 kPa and a crossflow velocity of 6.7 m/s, using a tubular single stainless steel module that consisted of three ceramic tubes, each with 19 channels (3.5 mm inner diameter) and a length of 0.5 m. For MF with 100 nm and 50 nm pore diameters, the recovery yield of major serum proteins in permeate was 44.3% and 44.1%, while the recovery yield of minor serum proteins was slightly less by 0%–8% than 50 nm MF. MF with 20 nm pore diameters showed a markedly lower (by 12%–45%) recovery yield for both major and minor serum proteins, corresponding with its lower membrane flux. Flux sharply decreased with an increasing concentration factor (CF) up to four, and thereafter remained almost unchanged. Compared to the decrease (88%) of flux, the transmission of major and minor serum proteins was decreased by 4%–15% from CF = one to CF = eight. With increasing processing stages, the flux gradually increased, and the recovery yield of both major and minor proteins in the permeate gradually decreased and reached a considerably low value at stage five. After four stages of MF with 100 nm pore diameter and a CF of four for each stage, the cumulative recovery yield of major serum proteins, IgG, IgA, IgM, LF, LPO, and XO reached 95.7%, 90.8%, 68.5%, 34.1%, 15.3%, 39.1% and 81.2% respectively.

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Development and Validation of a Method for the Quantification of Milk Proteins in Food Products Based on Liquid Chromatography with Mass Spectrometric Detection

Journal of AOAC International ◽

10.1093/jaoac/94.4.1043 ◽

2011 ◽

Vol 94 (4) ◽

pp. 1043-1059 ◽

Cited By ~ 38

Author(s):

Petra Lutter ◽

Véronique Parisod ◽

Hans Weymuth

Keyword(s):

Milk Powder ◽

Skim Milk ◽

Internal Standard ◽

Milk Proteins ◽

Skim Milk Powder ◽

Selected Reaction Monitoring ◽

Validation Data ◽

Development And Validation ◽

Protein Rich ◽

Β Lactoglobulin

Abstract The protection of allergic consumers is crucial to the food industry. Therefore, accurate methods for the detection of food allergens are required. Targeted detection of selected molecules by MS combines high selectivity with accurate quantifcation. A confrmatory method based on LC/selected reaction monitoring (SRM)-MS/MS was established and validated for the quantifcation of milk traces in food. Tryptic peptides of the major milk proteins β-lactoglobulin, β-casein, αS2-casein, and κ-casein were selected as quantitative markers. Precise quantifcation was achieved using internal standard peptides containing isotopically labeled amino acids. For each peptide, qualifer and quantifer fragments were selected according to Commission Decision 2002/657/EC. A simple sample preparation method was established without immunoaffnity or SPE enrichment steps for food matrixes containing different amounts of protein, such as baby food, breakfast cereals, infant formula, and cereals. Intermediate reproducibility, repeatability, accuracy, and measurement uncertainty were determined for each matrix. LOD values of 0.2–0.5 mg/kg, e.g., for β-lactoglobulin, were comparable to those obtained with ELISA kits. An LOQ of approximately 5 mg/kg, expressed as mass fraction skim milk powder, was validated in protein-rich infant cereals. The obtained validation data show that the described LC/SRM-MS/MS approach can serve as a confrmatory method for the determination of milk traces in selected food matrixes.

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Influence of Processing Temperature on Membrane Performance and Characteristics of Process Streams Generated during Ultrafiltration of Skim Milk

Foods ◽

10.3390/foods9111721 ◽

2020 ◽

Vol 9 (11) ◽

pp. 1721

Author(s):

Ritika Puri ◽

Upendra Singh ◽

James A. O’Mahony

Keyword(s):

Inverse Relationship ◽

Skim Milk ◽

Biochemical Properties ◽

Processing Temperature ◽

Casein Micelle ◽

Plasmin Activity ◽

Membrane Performance ◽

Flux Decline ◽

Dairy Ingredients ◽

Β Lactoglobulin

The effects of processing temperature on filtration performance and characteristics of retentates and permeates produced during ultrafiltration (UF) of skim milk at 5, 20, and 50 °C were investigated. The results indicate that despite higher flux at 50 °C, UF under these conditions resulted in greater fouling and rapid flux decline in comparison with 5 and 20 °C. The average casein micelle diameter was higher in retentate produced at 5 and 20 °C. The retentate analysed at 5 °C displayed higher viscosity and shear thinning behaviour as compared to retentate analysed at 20 and 50 °C. Greater permeation of calcium and phosphorus was observed at 5 and 20 °C in comparison with 50 °C, which was attributed to the inverse relationship between temperature and solubility of colloidal calcium phosphate. Permeation of α-lactalbumin was observed at all processing temperatures, with permeation of β-lactoglobulin also evident during UF at 50 °C. All UF retentates were shown to have plasmin activity, while lower activity was measured in retentate produced at 5 °C. The findings revealed that UF processing temperature influences the physicochemical, rheological, and biochemical properties of, and thereby govern the resulting quality and functionality of, retentate- and permeate-based dairy ingredients.

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High-pressure treatment of milk: effects on casein micelle structure and on enzymic coagulation

Journal of Dairy Research ◽

10.1017/s0022029999004021 ◽

2000 ◽

Vol 67 (1) ◽

pp. 31-42 ◽

Cited By ~ 130

Author(s):

ERIC C. NEEDS ◽

ROBERT A. STENNING ◽

ALISON L. GILL ◽

VICTORIA FERRAGUT ◽

GILLIAN T. RICH

Keyword(s):

Whey Proteins ◽

Skim Milk ◽

Casein Micelle ◽

Casein Micelles ◽

Dense Networks ◽

Protein Levels ◽

Micelle Structure ◽

Milk Casein ◽

Β Lactoglobulin ◽

Gel Network

High isostatic pressures up to 600 MPa were applied to samples of skim milk before addition of rennet and preparation of cheese curds. Electron microscopy revealed the structure of rennet gels produced from pressure-treated milks. These contained dense networks of fine strands, which were continuous over much bigger distances than in gels produced from untreated milk, where the strands were coarser with large interstitial spaces. Alterations in gel network structure gave rise to differences in rheology with much higher values for the storage moduli in the pressure-treated milk gels. The rate of gel formation and the water retention within the gel matrix were also affected by the processing of the milk. Casein micelles were disrupted by pressure and disruption appeared to be complete at treatments of 400 MPa and above. Whey proteins, particularly β-lactoglobulin, were progressively denatured as increasing pressure was applied, and the denatured β-lactoglobulin was incorporated into the rennet gels. Pressure-treated micelles were coagulated rapidly by rennet, but the presence of denatured β-lactoglobulin interfered with the secondary aggregation phase and reduced the overall rate of coagulation. Syneresis from the curds was significantly reduced following treatment of the milk at 600 MPa, probably owing to the effects of a finer gel network and increased inclusion of whey protein. Levels of syneresis were more similar to control samples when the milk was treated at 400 MPa or less.

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Heat-induced interactions of β-lactoglobulin and α-lactalbumin with the casein micelle in pH-adjusted skim milk

International Dairy Journal ◽

10.1016/s0958-6946(00)00087-x ◽

2000 ◽

Vol 10 (8) ◽

pp. 509-518 ◽

Cited By ~ 84

Author(s):

David J Oldfield ◽

Harjinder Singh ◽

Michael W Taylor ◽

Kevin N Pearce

Keyword(s):

Skim Milk ◽

Casein Micelle ◽

Β Lactoglobulin

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Influence of denaturation and aggregation of β-lactoglobulin on rennet coagulation properties of skim milk and ultrafiltered milk

Food Research International ◽

10.1016/s0963-9969(97)00011-2 ◽

1996 ◽

Vol 29 (8) ◽

pp. 715-721 ◽

Cited By ~ 27

Author(s):

Algane Waungana ◽

Harjinder Singh ◽

Rodney J. Bennett

Keyword(s):

Skim Milk ◽

Rennet Coagulation ◽

Β Lactoglobulin

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Heat stability of milk

Journal of Dairy Research ◽

10.1017/s0022029900021075 ◽

1980 ◽

Vol 47 (2) ◽

pp. 199-210 ◽

Cited By ~ 20

Author(s):

Donald F. Darling

Keyword(s):

Temperature Dependence ◽

Elevated Temperatures ◽

Skim Milk ◽

Heat Stability ◽

Coagulation Time ◽

Ph Values ◽

Protein Polymerization ◽

Casein Protein ◽

Apparent Activation Energies ◽

Β Lactoglobulin

SummaryThe heat stability of a standard reconstituted skim-milk preparation has been investigated as a function of pH, temperature of coagulation, and forewarming treatment. Apparent activation energies have been calculated from the temperature dependence of coagulation time, and a constant value of 144 kJ/mole has been found for milks between pH 6·6 and 6·9. The effect of forewarming resulted in a decrease in stability at the most acid pH values, a slight increase at higher pH but below the pH maximum, and a decrease in the region of the pH minimum. A working hypothesis is proposed for the mechanisms leading to the coagulation of milk at elevated temperatures, based upon Ca induced precipitation of casein, protein polymerization, β-lactoglobulin: κ-casein interaction, and precipitation of insoluble Ca phosphates.

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