Analysis of natural milk and milk poweder samples by NAA

As a part of the Iraqi Food Analysis Programme /I.F.A.P./ the concentration of Na, Mg, P, Cl, K, Ca, Zn, Se, Br, Rb and I in natural milk collected from different regions of Iraq, and in milk powder samples have been determined by using the NAA technique. It was found that except for the elements I, Rb and Br the concentration of the elements was approximately identical in both the natural milks and milk powders.     

Rapid trace determination of radiostrontium in milk and drinking water

A rapid method for determining traces of radiostrontium in milk and drinking water is described. The technique involves a batch treatment of the milk sample with a cation exchanger (DOWEX 50W X8) followed by a solvent extraction with a crown ether (DC18C6) and a precipitation of SrCO₃. In the case of water, the strontium is extracted directly with the crown ether. The average separation yield is 74% for milk and 91% for water. The overall separation procedure takes about 8 hours. Activities as low as 0.03 Bq/1 can be determined with a low background GM-counter.     

Thermal behaviour of milk powders studied by differential thermal analysis and heat flow calorimetry

The technique of heat flow calorimetry was used to study the thermal behaviour of different milk powders above 20°C. Exothermic reactions of different types occurred when measurements were made with the samples in sealed cells. According to our interpretation of the calorimetric curves, these reactions correspond to: crystallization of amorphous lactose, Maillard reaction between milk proteins and lactose, oxidation of milk fat and decomposition of lactose. Their relative importance is discussed. In addition, the technique of high-pressure differential thermal analysis was used for studying spontaneous ignition and combustion of milk powders, under a large oxygen excess. The role of fat, carbohydrate and protein decomposition is underlined. Some self-ignition temperature values are given.     

Raman spectroscopy based analysis of milk using random forest classification

The development of a classification system based on the Raman spectra of milk samples is proposed in present study. Such development could be useful for nutritionists in suggesting healthy food to infants for their proper growth. Previously, molecular structures in milk samples have been exploited by Raman spectroscopy. In the current study, Raman spectral data of milk samples of different species is utilized for multi-class classification using a dimensionality reduction technique in combination with random forest (RF) classifier. Quantitative and experimental analysis is based on locally collected milk samples of different species including cow, buffalo, goat and human. This classification is based on the variations (different concentrations of the components present in milk such as proteins, milk fats, lactose etc.) in the intensities of Raman peaks of milk samples. Principal component analysis (PCA) is used as a dimensionality reduction technique in combination with RF to highlight the variations which can differentiate the Raman spectra of milk samples from different species. The proposed technique has demonstrated sufficient potential to be used for differentiation between milk samples of different species as the average accuracy of about 93.7%, precision of about 94%, specificity of about 97% and sensitivity of about 93% has been achieved.     

Electrospray ionization and tandem ion trap mass spectrometry for the confirmation of seven beta-lactam antibiotics in bovine milk

The feasibility of a technique to confirm the presence of residues from seven beta-lactam antibiotics in bovine milk has been demonstrated. The technique makes use of electrospray ionization and tandem ion trap mass spectrometry. Residues are first extracted from milk by reversed-phase solid phase extraction. Target analytes are separated by on-line reversed-phase liquid chromatography and ionized in the electrospray interface. The product ion mass spectra are acquired following collision-induced dissociation of protonated molecules. Confirmation is based on comparison of full scan spectra between unknowns and bona fide standards. The feasibility of this technique has been demonstrated for the six beta-lactams currently approved for use in lactating dairy cattle (penicillin G, ampicillin, amoxicillin, cloxacillin, cephapirin and ceftiofur) and a drug not approved for animal use, cefazolin. The technique has been applied to control milk fortified at 5 ng/mL of penicillin G and 10 ng/mL of the other six drugs.     

Determination of melamine in milk powder using gas chromatography-high-resolution isotope dilution mass spectrometry

A GC-high-resolution isotope dilution MS (IDMS) method for the quantification of melamine in milk powder is described. The developed technique is compared to the LC-IDMS/MS technique, typically used for the determination of melamine in various matrices. The accuracy of the GC-high-resolution IDMS method was demonstrated when a small degree of equivalence was obtained in a regional comparative study involving the determination of melamine in milk powder.     

Determination of lead and cadmium in milk by electrothermal atomic absorption spectrophotometry

The concentration of lead and cadmium in different kinds of milk samples (powdered, infant formula, market, buffalo, condensed and human) were determined using electrothermal atomic absorption spectrophotometric technique. Among all the varieties of milk analysed, condensed milk was found to contain much higher amount of lead. Human milk as expected was found to have lowest concentration of these elements. The results were compared with the reported values of other countries. Daily intake of these toxic elements by adults and babies up to the age of six months through the consumption of various types of milk was estimated and compared with the tolerance levels.     

Distribution of strontium in milk component

The distribution of strontium between the milk components, i.e., serum, casein micelles, whey and hydroxyapatite was determined. The sorption on hydroxyapatite was investigated using batch method and radiotracer technique. The aqueous phase comprised of either milk or whey. The sorption of strontium on hydroxyapatite depended on the method of its preparation and on the composition of the aqueous phase. The sorption of strontium was increased with an increase of pH. The presence of citrate species resulted in decrease of the sorption of strontium on hydroxyapatite. The sorption of ⁸⁵Sr on hydroxyapatite decreased with the increasing concentration of Ca²⁺ ions. Addition of Ca²⁺ ions to milk resulted in milk pH decrease. The decrease in pH value after calcium addition to milk is related to exchanges between added calcium and micellar H⁺. The average value of strontium sorption on casein micelles in milk with presence of hydroxyapatite was (47.3 ± 5.6) %. The average value of sorption of ⁸⁵Sr on casein micelles in milk without the addition of hydroxyapatite was (68.9 ± 2.2) %.     

Radioanalytical determination of137Cs and89Sr in milk

Separation of Cs, Sr and Ca from their mixture was studied using solvent extraction and ion exchange techniques. More than 90% separation efficiency was achieved for Ca–Sr separation using ion exchange resin (Doulite C-20) while solvent extraction amounted to 88%. A proposed technique for determination of¹³⁷Cs and⁸⁹Sr in milk (after removal of organic matter) showed more than 80% accuracy for⁸⁹Sr determination and more than 90% for¹³⁷Cs determination.     

Determination of biotin and folate in infant formula and milk by optical biosensor-based immunoassay

Biomolecular interaction analysis was evaluated for the automated analysis of biotin- and folate-supplemented infant formulas and milk powders. The technique was configured as a biosensor-based, nonlabeled inhibition immunoassay using monoclonal antibodies raised against analyte-conjugate. Sample extraction conditions were optimized and antibodies were evaluated for cross-reactivity. Performance parameters included a quantitation range of 2-70 ng/mL, recoveries of 86-102%, agreement against assigned reference values for National Institute of Standards and Technology Standard Reference Material 1846, between-laboratory reproducibility relative standard deviation of 9.1% for biotin and 8.1% for folate, respectively, and equivalence against reference microbiological assay methods for both analytes.     

Determination of minor proteins of bovine milk and colostrum by optical biosensor analysis

Automated, rapid, sensitive, and label-free biosensor-based immunoassays for immunoglobulin G (IgG), folate binding protein, lactoferrin, and lactoperoxidase in bovine milk using surface plasmon resonance optical detection with direct binding assay format are described. Samples are prepared for analysis by direct dilution into buffer. Analysis conditions, including ligand immobilization, flow rate, contact time, and regeneration are defined and nonspecific binding considerations evaluated. The technique has been applied to the measurement of these proteins in consumer milks, colostrum, milk products, and infant formulas, and their temporal change during early bovine lactation followed.     

Colloidal transport phenomena of milk components during convective droplet drying

Material segregation has been reported for industrial spray-dried milk powders, which indicates potential material migration during drying process. The relevant colloidal transport phenomenon and the underlying mechanism are still under debate. This study extended the glass-filament single droplet drying technique to observe not only the drying behaviour but also the dissolution behaviour of the correspondingly dried single particle. At progressively longer drying stage, a solvent droplet (water or ethanol) was attached to the semi-dried milk particle and the interaction between the solvent and the particle was video-recorded. Based on the different dissolution and wetting behaviours observed, material migration during milk drying was studied. Fresh skim milk and fresh whole milk were investigated using water and ethanol as solvents. Fat started to accumulate on the surface as soon as drying was started. At the initial stage of drying, the fat layer remained thin and the solubility of the semi-dried milk particle was much affected by lactose and protein present underneath the fat layer. Fat kept accumulating at the surface as drying progressed and the accumulation was completed by the middle stage of drying. The results from drying of model milk materials (pure sodium caseinate solution and lactose/sodium caseinate mixed solution) supported the colloidal transport phenomena observed for the milk drying. When mixed with lactose, sodium caseinate did not form an apparent solvent-resistant protein shell during drying. The extended technique of glass-filament single droplet approach provides a powerful tool in examining the solubility of individual particle after drying.     

The certification of the iodine content of two spiked skim milk powders

Summary The Certification of the Iodine Content of Two Spiked Skim Milk Powders The certification of the iodine content in the BCR certified reference materials 150 and 151 is described. In particular the methods and their results are presented. The certified values are based on the results of 8–10 laboratories, of which each applied a different analyical technique.     

Qualitative and quantitative analysis of proteins and peptides in milk products by capillary electrophoresis

Milk protein is an important component of the human diet throughout much of the world. The ability to assess the relative composition and integrity of milk proteins or peptides in dairy foods or food ingredients is important because these molecules have a profound effect on product functionality and quality. This communication describes two capillary electrophoretic methods that are useful for the analysis of proteins and casein-derived peptides in cheese and milk products. One technique, which uses a buffer containing citrate/phosphate (pH 3.3), 4 M urea, and a polymeric additive in a coated capillary, is useful for qualitative and quantitative analysis of proteins and peptides in milk, cheese, and whey products. The second method employs a citrate/phosphate buffer (pH 2.8) and a bare silica capillary, and is well suited for the analysis of small, casein-derived peptides in aqueous cheese extracts.     

Selective solid-phase extraction of dibutyl phthalate from soybean milk using molecular imprinted polymers

An analysis method is reported for dibutyl phthalate and related compounds with high selectivity and sensitivity by using the selective molecularly imprinted solid-phase extraction (MISPE) technique. In this report, dibutyl phthalate (DBP) is employed as the template molecule, and the molecularly imprinted polymers (MIPs) are synthesized through the bulk polymerization of methacrylic acid (MAA). The Scatchard plot suggests that the template-polymer system has two-site binding behavior with the dissociation constants of 0.5187 and 0.01898 mmol L⁻¹, respectively. The rebinding test, based on the MISPE column technique, shows the recoveries of soybean milk samples spiked with 5 phthalates are in the range of 75.8-107.5% with the relative standard deviations of 1.80-10.08%, indicating the feasibility of the prepared MIPs for phthalates extraction. Finally, the method is used to analyze the trace level of phthalates in commercial soybean milk.     

Validation of capillary electrophoresis in the analysis of ewe's milk casein

Recent investigations have shown that capillary electrophoresis (CE) can be an alternative to other techniques such as polyacrylamide gel electrophoresis (PAGE) or sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in the qualitative analysis and separation of the different casein fractions in cow's and ewe's milk. However, past work has not yet clarified whether that method can achieve good quantifications. The present study has used a commercial whole ovine casein standard and a mixture of the standard and whole casein extracted from ewe's milk cheese to test the reliability of the technique. The results show that CE was able to quantify the ewe's milk caseins. The areas under four of the most representative peaks on the electrophoretogram for two alpha and two beta-caseins (designated alpha-casein1CE, alpha-casein2CE, beta-casein1CE, and beta-casein2CE in order of elution) were used to validate the method. In relation to linearity, coefficient of determination (r2) values greater than 99% were obtained for the regressions of each of the caseins. Moreover, each casein yielded response factors with a relative standard deviation (R.S.D.) of less than or equal to 5. The coefficients obtained in the day-to-day reproducibility analysis were higher than those for the same-day repeatability, but all the values were within acceptable limits. In the study of accuracy, the percentage recovery rates for the alpha-casein fractions were higher than those for the beta-casein fractions, hence quantification of the latter using this technique would appear to be more accurate under the conditions employed.     

Nano-HPLC-mass spectrometry and MEKC for the analysis of oligosaccharides from human milk

The separation of oligosaccharides derivatized with various esters of aminobenzoic acid by means of reversed-phase nano-HPLC (nHPLC) with on-line ESI mass spectrometry and off-line MALDI-TOF mass spectrometry as well as MEKC is described. For this purpose methyl, ethyl and butyl aminobenzoates and heptyloxyaniline were used as derivatization agents for homologous maltodextrins and oligosaccharides from human milk. Four different C(18) stationary phases were tested for this purpose because the type of stationary phase was shown to have a dramatic effect on the performance of the separation. Optimal results were obtained using n-butyl aminobenzoate as label and an encapsulated ODS stationary phase. The on-line coupling of nHPLC to ESI MS allowed to separate and identify various oligosaccharides from human milk. This technique enabled the exact attribution of the molecular structure to a signal in the chromatogram. In a second approach oligosaccharides were separated by nHPLC and subsequently fractionated. The fractions were analyzed by MALDI-TOF mass spectrometry. The results obtained by this approach confirmed the ESI MS data. An analogous separation profile was obtained by using sodium dodecyl sulfate in MEKC, which proves that the retention mechanisms of both techniques are identical.     

A preliminary study of milk powder hydration using TEDSpiL continuous wave NMR

Moisture content of foodstuffs are typically assessed by Titration or Near Infrared Spectroscopy, which are labour-intensive as a manual measurement or costly when automated. Magnetic resonance offers a method for moisture evaluation but is also normally costly. In this work, we revisit Look and Locker's “Tone Burst” experiment with a marginal oscillator to evaluate moisture content of powdered–skimmed milk subjected to increased humidity. We refer to this technique as the Transient Effect Determination of Spin–Lattice (TEDSpiL) relaxation times. Moisture content in the samples ranged from 0–12% as determined from the weight gained by the dry powder when re-suspended in water to reach a concentration of 40% w/v. The relaxation properties of re-hydrated samples were measured with a CW NMR sensor. Solutions made up from powders with a higher retained moisture content provided lower measured relaxation values providing a method of measuring the moisture content of the powder. This technique provides a moisture measurement in under 5∼s compared with several minutes for the equivalent pulsed method using low-field hardware.     

Simultaneous determination of total and free calcium in milk by flow injection

A fast and reliable procedure for the determination of total and free calcium in milk is described. The method is based on the flow injection (Fl) technique. Total calcium is determined by atomic absorption spectrometry (AAS) (422.7 nm) and free calcium by spectrophotometry (580 nm). Interference in the determination of free calcium is eliminated by using a dialyser, which also separates the total and free calcium. Interference from phosphates in milk in the determination of total calcium by AAS is overcome by using a dinitrogen oxide-acetylene flame with the necessary suppression with K+. With 30-microliters samples the Fl system covers a standard working range of 100-1500 mg dm-3 of Ca2+. The system is suitable for the simultaneous determination of total calcium (relative standard deviation less than 1.30% for 1300-1500 mg dm-3 of total calcium) and free calcium (relative standard deviation less than 0.85% for 120-170 mg dm-3 of free calcium) in milk at a sampling frequency of about 60 samples h-1. The results obtained agree reasonably well with results from the AAS method.     

Application of strategically designed sample composition to the rapid analytical screening of milk samples for polychlorinated biphenyls

Strategically designed sample composition (SSC) is a new technique that decreases the number of analytical determinations needed in routine screening to as few as the number of original sample specimens while providing information that is specific to them. Although this new technique has been applied to environmental studies, this paper describes its first application to food safety studies. Contamination of milk samples with polychlorinated biphenyls (PCBs) was chosen as a case study to show the usefulness and potential of the SSC technique with a fast analytical procedure that involves saponification of the samples and solid-phase microextraction of the PCBs. A total of 20 sample specimens can be analyzed in 11 determinations with excellent predictions of the positive samples and the concentration levels of the contaminants. The robustness of the strategy was investigated and demonstrated.