Analysis of α-lactalbumin, β-lactoglobulin A and B in whey protein powder, colostrum, raw milk, and infant formula by CE and LC

Structural and chemical changes induced by temperature and pH hinder the digestibility of whey proteins

In the food and feed industry, protein extraction is commonly performed under acid or basic conditions, combined with heat, in order to increase the extraction yield. Under severe processing conditions, proteins may undergo molecular modifications. Here, the effects of heating (30, 60, 90 °C) at different pH values (2, 7, 9, 11, 13) were evaluated on commercial whey proteins, used as a simplified protein model. The main structure and chemical modifications concerning protein aggregation, hydrolysis, insolubilization, amino acid degradation and racemization were investigated in detail. Using in vitro static models, the degree of protein hydrolysis and the released peptides were determined after the digestive process. Accumulation of molecular modifications was mostly observed after basic pH and high temperatures treatments, together with a marked decrease and modification of the digestibility profile. Instead, protein digestibility increased in neutral and acidic conditions in a temperature-dependent manner, even if some modification in the structure occurs.

Capillary electrophoresis with dual C4D/UV detection for simultaneously determining major metal cations and whey proteins in milk

A reliable and simple CE method with dual C⁴D and UV detection modes for simultaneous determination of major metal cations and whey proteins in milk samples was developed. Sample pretreatment comprised dilution, acidification to pH 4.55 with 10 mM AcOH and centrifugation. The complete separation of metal cations K⁺, Ca²⁺, Na⁺, and Mg²⁺ and whey proteins α-Lac, and β-Lg could be achieved respectively within 10 min and 20 min in a simple BGE composed of 1.0 M AcOH, 12 mM l-His and 2 mM 18-crown-6 with pH 2.74 at a voltage/current of +15 kV/12.5 μA. The samples were injected hydrodynamically by a pressure of 50 mbar for 5 s, the excitation voltage and excitation frequency of the C⁴D detector were 80 V and 1000 kHz, respectively and the detection wavelength of UV detection was set at 200 nm. In cation analysis, the range of the detection limit was 0.05-0.10 mg L^-1 for C⁴D detection and 0.10-0.50 mg L^-1 for UV detection, respectively, and the relative standard deviations (RSD%, n = 5) of intraday and interday analysis were 0.37-0.55% and 0.46-0.79% for the relative migration time, and 2.51-4.12% and 3.65-4.91% for the peak area, respectively. In whey protein analysis, the detection limits of β-Lg and α-Lac analysis were 5 mg L^-1 and 3 mg L^-1, respectively and the relative standard deviations (RSD%, n = 5) of intraday and interday analysis were 0.29-0.31% and 0.43-0.48% for the migration time and 2.89-3.25% and 3.29-4.18% for the peak area, respectively. The content of four major metal cations and two whey proteins in various types of milk samples was obtained. The results indicated that the content of metal cations varied little in milk samples of different brands and prices, while the content of whey proteins, as thermosensitive active proteins, varied greatly among different heat-treated milk samples.

FTIR Spectroscopic Study of the Secondary Structure of Globular Proteins in Aqueous Protic Ionic Liquids

Protein misfolding is a detrimental effect which can lead to the inactivation of enzymes, aggregation, and the formation of insoluble protein fibrils called Amyloids. Consequently, it is important to understand the mechanism of protein folding, and under which conditions it can be avoided or mitigated. Ionic liquids (ILs) have previously been shown as capable of increasing or decreasing protein stability, depending on the specific IL, IL concentration and which protein. However, a greater range of IL-proteins need to be systematically explored to enable the development of structure-property relationships. In this work, the secondary structure of four proteins, lysozyme, trypsin, β-lactoglobulin and α-amylase, were studied in aqueous solutions of 10 protic ionic liquids (PILs) with 0-50 mol% PIL present. The PILs consisted of ethyl-, ethanol-, diethanol- and triethanolammonium cations paired with nitrate, formate, acetate or glycolate anions. The secondary structure was obtained using ATR-FTIR spectroscopy. It was found that lysozyme and trypsin retained its secondary structure, consistent with a native folded state, for many of the aqueous IL solutions which contained a formate or nitrate anion at the most dilute concentrations. In contrast, α-amylase and β-lactoglobulin generally had poor stability and solubility in the IL solutions. This may be due to the isoelectric point of α-amylase and β-lactoglobulin being closer to the pH of the solvents. All four proteins were insoluble in ethyl-, ethanol- and diethanolammonium acetate, though α-amylase and trypsin retained their secondary structure in up to 20 and 30 mol% of triethanolammonium acetate, respectively. It was evident that the protein stability varied substantially depending on the protein-IL combination, and the IL concentration in water. Overall, the findings indicated that some ions and some ILs were in general better for protein solubility and stability than others, such as acetate leading to poor solubility, and EAN and EAF generally leading to better protein stability than the other PILs. This study of four proteins in 10 aqueous PILs clearly showed that there are many complexities in their interactions and no clear general trend, despite the similarities between the PIL structures. This highlights the need for more and larger studies to enable the selection and optimization of PIL solvents used with biomolecules.

Effect of droplet lifetime on where ions are formed in electrospray ionization

The location of gaseous ion formation in electrospray ionization under native mass spectrometry conditions was investigated using theta emitters with tip diameters between 317 nm and 4.4 μm to produce droplets with lifetimes between 1 and 50 μs.

Simultaneous detection of α-Lactoalbumin, β-Lactoglobulin and Lactoferrin in milk by Visualized Microarray

BACKGROUND

α-Lactalbumin (a-LA), β-lactoglobulin (β-LG) and lactoferrin (LF) are of high nutritional value which have made ingredients of choice in the formulation of modern foods and beverages. There remains an urgent need to develop novel biosensing methods for quantification featuring reduced cost, improved sensitivity, selectivity and more rapid response, especially for simultaneous detection of multiple whey proteins.

RESULTS

A novel visualized microarray method was developed for the determination of a-LA, β-LG and LF in milk samples without the need for complex or time-consuming pre-treatment steps. The measurement principle was based on the competitive immunological reaction and silver enhancement technique. In this case, a visible array dots as the detectable signals were further amplified and developed by the silver enhancement reagents. The microarray could be assayed by the microarray scanner. The detection limits (S/N = 3) were estimated to be 40 ng/mL (α-LA), 50 ng/mL (β-LG), 30 ng/mL (LF) (n = 6).

CONCLUSIONS

The method could be used to simultaneously analyze the whey protein contents of various raw milk samples and ultra-high temperature treated (UHT) milk samples including skimmed milk and high calcium milk. The analytical results were in good agreement with that of the high performance liquid chromatography. The presented visualized microarray has showed its advantages such as high-throughput, specificity, sensitivity and cost-effective for analysis of various milk samples.

Bioanalytical methods for food allergy diagnosis, allergen detection and new allergen discovery

For effective monitoring and prevention of the food allergy, one of the emerging health problems nowadays, existing diagnostic procedures and allergen detection techniques are constantly improved. Meanwhile, new methods are also developed, and more and more putative allergens are discovered. This review describes traditional methods and summarizes recent advances in the fast evolving field of the in vitro food allergy diagnosis, allergen detection in food products and discovery of the new allergenic molecules. A special attention is paid to the new diagnostic methods under laboratory development like various immuno- and aptamer-based assays, including immunoaffinity capillary electrophoresis. The latter technique shows the importance of MS application not only for the allergen detection but also for the allergy diagnosis.

Development of an SI-Traceable HPLC-Isotope Dilution Mass Spectrometry Method To Quantify β-Lactoglobulin in Milk Powders

β-Lactoglobulin (β-LG) is one of the major allergenic proteins in milk. There is an urgent demand for an accurate and traceable method to develop β-LG certified reference material (CRM). In this work, β-LG was enzymatically digested and a specific peptide was chosen for quantitation by isotope-dilution mass spectrometry (IDMS). With amino acid CRMs as standards, the results could be traced to SI unit. By the proposed method, the recovery ranged from 86.0% to 118.3% with CVs <9.0%. The LOD and LOQ were 4.8 × 10^-5 g/g and 1.6 × 10^-4 g/g of β-LG in milk powder, respectively. Ten samples from domestic market were analyzed with CVs <5.6%, and the relative expanded uncertainties ranged from 4.2% to 5.9% (k = 2). With the CRMs, it is expected that the comparability of β-LG quantitation results will be improved among different laboratories.