HPLC/UV analysis of proteins in dairy products using a hydrophobic interaction chromatographic column

A novel ultra-high performance liquid chromatography method for the rapid determination of β-lactoglobulin as heat load indicator in commercial milk samples

The level of undenatured acid-soluble β-lactoglobulin can be used as an indicator to assess the heat load applied to liquid milk, thus further allowing the discrimination between milk originating from different thermal production processes. In this work, a new UHPLC method for the rapid determination of bovine β-lactoglobulin in 1.8min only (total runtime 3min) is presented using simple UV detection at 205nm. Separation selectivity for possibly co-eluting other major whey proteins (bovine serum albumin, lactoferrin, α-lactalbumin, immunoglobulin G) was verified, and the method validated for the analysis of liquid milk samples regarding linearity (20-560μg/mL, R(2)>0.99), instrumentation precision (RSDs<2.8%), limits of detection and quantification (7 and 23mg/L milk), repeatability of sample work-up (RSDs≤2.6%) and method recovery (103%). In total, 71 commercial liquid milk samples produced using different preservation techniques (e.g., thermal or mechanical treatment), hence featuring different applied heat loads, were profiled for their intrinsic undenatured acid-soluble β-lactoglobulin levels. As expected, pasteurized milk showed the highest concentrations clearly above 3000mg/L due to pasteurization being the mildest thermal treatment, while in contrast, ultra-high temperature heated milk featured the lowest amounts (<200mg/L). For extended shelf life (ESL) milk, quite diverse levels were determined ranging from ∼100 up to 4000mg/L, thus clearly illustrating variable applied heat loads and impacts on the "nativeness" of milk essentially due to the fact that the production technologies used for ESL milk may differ significantly, and are currently not regulated in the EU.

Size exclusion and reversed-phase high-performance liquid chromatography/UV for routine control of thermal processing of cows' and donkey milk major proteins

Cows' and donkey milks (raw and thermally processed) and respective whey were analysed for quantification of major proteins. Two different chromatographic approaches, size exclusion (SE-HPLC) and reversed-phase high performance liquid chromatography (RP-HPLC) both coupled to UV detection were used. Usefulness of these methods for routine control of the effect of thermal processing was evaluated. The external standard method was used to calibrate the SE-HPLC and RP-HPLC systems. Concerning quantification of β-lactoglobulin (β-lg), α-lactalbumin (α-la), lysozyme (lys), and total casein (cn), no significant differences between results obtained by SE-HPLC and by RP-HPLC (t-test, P>0·05) were observed for raw milks and whey. Heating of cows' milk promoted aggregation of denatured proteins as observed by SE-HPLC, whereas α-la and β-lg from donkey milk were stable to thermal processing at 100°C (5 min). Lys was quantified in donkey raw milk and whey however, in thermally processed donkey milk lys was denatured and could not be quantified by HPLC.

Quantification of bovine casein fractions by direct chromatographic analysis of milk. Approaching the application to a real production context

The ability to quantify the casein content by an exact and cost-effective approach represents an issue of crucial importance in the dairy industry as the natural variations in milk protein concentration can markedly affect the yield of the cheesemaking processes, thus causing a direct and significant economic impact on the producers. In this work, the separation and quantification of alpha(s1)-, alpha(s2)-, kappa- and beta-casein was carried out by direct RP-HPLC analysis of milk. The identification of each casein was established by electrospray ionization mass spectrometry. The data show that this method is able to effectively separate the bovine casein fractions, it provides simplified analytical conditions (with special regard to mobile phase composition and gradient profile) and faster separation while ensuring adequate precision to achieve reliable quantifications in milk samples from dairy production.

Rapid Determination of Vitellogenin in Fish Plasma by Anion Exchange High Performance Liquid Chromatography Using Postcolumn Fluorescence Derivatization with o-Phthalaldehyde

An analytical method involving anion exchange high performance liquid chromatographic determination of vitellogenin (Vtg) in fish plasma after postcolumn fluorescence derivatization with o-phthalaldehyde (OPA) was developed. The retention time of Vtg was about 11 min. The reagent variables for derivatization were optimized. The fluorophore was excited at 335 nm and detected at 435 nm. A calibration curve was established ranging from 0.13 to 11.28 microg. The determination limit of Vtg was found to be as low as 0.13 microg. The spiked recovery was 93.6% and interassay variability was less than 4%. The method developed was used to determine Vtg in fish plasma obtained from red sea bream (Pagrosomus major), black porgy (Sparus macrocephalus) and skew band grunt (Hapalogenys nitens), without complicated sample pretreatment. The results confirmed that the method showed advantages of being simple, rapid, reproducible and sensitive.

Modification of functional properties of egg-white proteins

Egg-white proteins are extensively utilised as food ingredients due to their unique functional properties. Several attempts have been made in order to improve the functional properties of egg-white proteins and to identify the optimal formulations for unique food products. Experimental data proves that controlled denaturation of egg-white proteins can have a beneficial impact on various functional applications in the food industry such as emulsifying ability, heat stability, and gelation. This review describes the effect of heat-induced denaturation on protein structure and functionality. Studies on the impact of Maillard reaction, which aim to elucidate the structure-function relationship of egg-white proteins, are presented. A novel approach which could be the basis for the development of new methods aiming to improve the functional properties of egg-white proteins is also discussed.

Detection and quantification of bovine, ovine and caprine milk percentages in protected denomination of origin cheeses by reversed-phase high-performance liquid chromatography of beta-lactoglobulins

A method for detecting and quantifying bovine, ovine and caprine milk mixtures in milk and cheeses by means of reversed-phase high-performance liquid chromatography (RP-HPLC) of beta-lactoglobulins is described. Gradient elution was carried out with a flow rate of 0.5 ml/min and a temperature of 45 degrees C, using a mixture of two solvents: solvent A (0.1% TFA in water) and solvent B (0.09% TFA in 80% aqueous acetonitrile, v/v). The effluent was monitored at 215 nm. Under the conditions used different chromatographic patterns were obtained for bovine, ovine and caprine whey proteins. Each milk type presented different retention times for beta-lactoglobulin peaks. Binary mixtures of bovine and ovine or bovine and caprine raw milks containing 1, 2, 5, 10, 20, 30, 50, 75 and 95% (v/v) of bovine milk, as well as ovine and caprine milk mixtures containing 1, 2, 5, 10, 20, 30, 50, 75 and 95% (v/v) of ovine milk were used for cheese making. Cheeses were prepared and ripened, according to traditional methods. Milk mixtures, fresh and ripened cheeses were analyzed. A linear relationship was established between log 10 of beta-lactoglobulin peaks ratio (calculated as peak area values ratio) and log 10 of the relative percentage of bovine or ovine milk. The ratio between beta-lactoglobulin peaks was not affected by the degree of ripening. Thus, enabling the quantification of milk type percentage, with a detection limit of 2%. This technique allowed quantification of milk species within the concentration range of 5-95%. The method was successfully applied for authenticity evaluation and quantitative determination of ovine and caprine milk percentages of commercial protected denomination of origin (PDO) cheeses.

Separation and quantification of the major casein fractions by reverse-phase high-performance liquid chromatography and urea-polyacrylamide gel electrophoresis. Detection of milk adulterations

The separation and quantification of bovine kappa-, alpha- and beta-caseins by HPLC-UV using an RP column which contained polystyrene-divinilbenzene copolymer based packing was optimized and validated. Gradient elution was carried out at a flow-rate of 1 ml/min and a temperature of 46 degrees C, using a mixture of two solvents. Solvent A was 0.1% trifluoroacetic acid in water and solvent B was acetonitrile-water-trifluoroacetic acid (95:5:0.1). The effluent was monitored by a UV detector at 280 nm. The determinations were performed in the linear range of 0.038-0.377 mg/ml for kappa-casein, 0.188-1.883 mg/ml for alpha-casein and 0.151-1.506 mg/ml for beta-casein. The detection limits were 0.006, 0.019 and 0.015 mg/ml for kappa-casein, alpha-casein and beta-casein, respectively. The validity of the method was verified. The recoveries ranged from 91 to 100% for bovine milk. The precision of the method was also evaluated, the RSD being less than 3.67%. The same HPLC procedure was used for the separation of caprine and ovine caseins. Different chromatographic profiles were obtained for bovine, ovine and caprine milks, although it was only possible to detect and quantify additions of 5% or more of bovine milk to caprine milk. With respect to detection of milk adulterations, electrophoresis using urea-polyacrylamide gel electrophoresis (PAGE) analysis was more sensitive. The evolution of casein proteolysis in cheeses made from bovine milk and cheeses made from ovine milk, during 30 days of ripening was followed by HPLC-UV and urea-PAGE methodologies. The results obtained by these techniques were similar.