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The addition of NaCl to milk is known to alter the mineral equilibrium and the structure of casein micelles. The objective of this study was to better understand the light scattering properties and viscosity of milk as a function of NaCl addition (0–500 mmol.L−1), for fresh skim milk and 2× concentrated milk protein. Suspensions (2×) were prepared using osmotic stressing. NaCl was added by dialyzing milk with milk serum (permeate) for 18 h. The presence of NaCl decreased the pH of milk and the zeta potential of casein micelles. When measured under diluted conditions, using dynamic light scattering, the average radius of the casein micelles showed a small increase, from 84 to 88 nm. Total calcium and phosphate in concentrated milk protein suspensions decreased with NaCl concentration, with a corresponding increase of the permeable calcium and phosphate, and of non-sedimentable caseins. In both untreated and concentrated milk protein samples, the viscosity increased with NaCl concentration. The characteristic decay time (τ) and turbidity measured under non-diluted conditions using diffusing wave spectroscopy showed a gradual decrease with NaCl addition. This work demonstrated that the changes to milk with addition of NaCl are mainly caused by the disruption of the internal structure of the casein micelles and changes in the composition of the serum phase, affecting the viscosity of the continuous phase as well as the refractive index contrast.

Speciation is important for good bioavailability of calcium from food and beverages. Effective calcium enrichment of dairy products for prevention of osteoporosis accordingly depends on the calcium compound added. Calcium d-lactobionate (50, 30 or 3 mM) was added to reconstituted skim milk with pH adjusted to 6.6, 6.0, 5.7 and 5.4 at 25 °C in order to investigate the distribution of calcium and phosphorus between micellar and serum phase and the speciation of calcium in the serum phase for enriched milk. The calcium from added calcium d-lactobionate was found to distribute between the micellar and serum phase at pH 6.6–6.0, while at pH 5.7–5.4, the added calcium remained in the serum phase. The concentration of phosphorus after enrichment was increased in the micellar phase and decreased in the serum phase at pH 6.6–6.0, while at pH 5.7–5.4, phosphorus remained constant in both phases. A decrease of total protein content and caseins in milk serum phase was observed after milk enrichment at all pH values as documented by protein determination and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Moreover, concentration of α-lactalbumin remained unchanged, while concentration of β-lactoglobulin decreased after addition of calcium d-lactobionate at all investigated pH values. Bioavailability of calcium from enriched dairy products depends on transfer to the micelles, and pH control is accordingly concluded to be critical for the use of calcium d-lactobionate for enrichment. The pH value needs to be taken into account when new calcium-enriched dairy products are designed to fulfil the primary role of having a product with high nutritional value and good calcium bioavailability.

The effects of ionic strength, pH and milk mineral composition on the adsorption of caseins and whey proteins on to particles of hydroxyapatite (HA) were studied by determining the amounts of adsorbed proteins on HA using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and by zeta-potential measurements. The amount of adsorbed proteins increased with increasing ionic strength from 0 to 0.1 M and decreasing pH from 8 to 6, for both sodium caseinate (SC) and whey protein isolate (WPI). In general, when the absolute value of the zeta-potential decreased because of changes in pH or ionic strength, more protein was found to adsorb on to the HA particles. This may be attributed to a decrease in the electrostatic repulsions between the HA particles and the protein species. The effects of the composition of the milk serum were investigated using simulated milk ultrafiltrate (SMUF). Both caseins and whey proteins adsorbed less on to HA particles in SMUF than on to HA particles in water. However, the effect of the composition of SMUF on the adsorption was less pronounced for caseins than for whey proteins. This may be related to the phosphorylated nature of the caseins. As the phosphate groups of the caseins bind more strongly to the HA binding sites than the carboxyl groups of the whey proteins, caseins might compete better with the phosphate and citrate ions in the milk serum for adsorption.

The two-stage production of microcapsules based on high- (HM) and low-methylated (LM) apple pectin complexes with milk serum β-lactoglobulin concentrate in an oil—water emulsion was developed. It was established that the ability of the pectin chains to form an effective secondary layer on the protein molecules surrounding the oil drops depended on the molecular weight and structure of the pectin. The obtained emulsions with HM- and LM-pectins and various pectin:protein ratios were capable of forming microcapsules of various sizes and different rifampicin contents. The proposed microcapsules could be used as potential drug carriers.

Lead is a heavy metal widely distributed in soil since it is constantly produced by the radioactive decay series of uranium (238U), actinium (235U), and thorium (232Th). The purpose of this research was to determine lead concentrations in fresh milk and derivates of the farms located in the municipalities of Pedra and Venturosa, in the state of Pernambuco, Brazil. The concentration of lead varied from 3 to 90 µg L−1 in fresh milk, from 20 to 1,050 µg kg−1 in curdled cheese, and from 6 to 20 µg L−1 in milk serum. Seven samples of fresh milk and one of curdled cheese presented concentration limits higher than those established by the Brazilian Ministry of Health.

Speciation of fission products (90Sr,99Tc,137Cs and152Eu) in raw cow milk was studied using the high-performance size exclusion radiochromatography (HP-SERC) by Biosep-SEC-S® column (Phenomenex, USA). The separation fraction were identified by a UV detector (280 nm) and a scintillation radiodetector. The mobile phase was Jenness-Koops buffer that simulated milk serum. Radiocesium was present only in non-protein fractions. The non-protein fractions complexed 17% of technetium and 57% of strontium. About 32% of strontium and 24% of europium were bound on the high molecular weight proteins (micellar casein). Low molecular weight proteins bound about 11% of strontium and 76% of europium. Non-size effects play a dominant role at HPSERC speciation of technetium, 83% of which follow the lightest fractions of milk.

Binding of added strontium by milk proteins under native conditions was investigated using pectin of various degrees of esterification. The partition of strontium, as well as cesium and europium, in aqueous two-phase milk-pectin system, is discussed in terms of “membraneless dialysis” and described by Donnan equilibria, and compared with the distribution between cation exchanger and milk, artificial milk serum, or pectin solutions. When going from pectin with a degree of esterification D.E.=93.2 to 61.4, the distribution of strontium decreases for about 40% in favor of pectin phase and this was explained by a relatively lower degree of dissociation of free carboxyle groups of pectin. The low-molecular fraction of added strontium in milk was assessed from Dowex 50×8 sorption data to be 31%, and that of cesium and europium 58% and 40%, respectively. However, distribution ratio of strontium and europium in milk/pectin system is much higher than it would correspond to the ion exchanger adsorption data.

Partition of radionuclides in aqueous liquid-liquid systems allows speciation of bioinorganic forms under nondenaturing conditions. From the fresh pasteurized skim bovine milk spiked with respective radionuclides and agitated with 4% w/w water solution of apple pectin, about 80% of cesium, 22% of strontium and less than 1.5% of europium is recovered with the pectin, phase at an initial milk — pectin volume ratio of 7∶3. This recovery fraction is proportional to the abundance of radionuclides in milk serum. No protein bound fraction of strontium extractable by Aerosol OT in isooctane was obtained. More than 3-fold preconcentration of strontium and europium radionuclides in milk is achieved after 10–15 min membraneless osmosis with pectin phase.

Human milk samples were assayed for bile-salt-stimulated lipolytic activity in the presence of an unpurified and purified preparation of glycoconjugated bile salts and two patterns of activity were obtained. One group of milks (high activity) had similar activities (mean +/- 1 S.D.) of 16.9 +/- 3.5 (purified bile salts) and 17.2 +/- 3.5 mumole . ml-1 . h-1 (unpurified bile salts) whereas another group (low activity) had a lower activity with the purified (4.2 +/- 2.3 mumole . ml-1 . h-1) than with the unpurified bile salt preparation (19.9 +/- 4.0 mumole . ml-1 . h-1). Activities of the low activity milks (assayed with the purified bile salts) could be increased following storage at -20 degrees C, sonication, or the preparation of an acetone ether powder and, in some cases, reached the maximal activity obtained with the unpurified bile salt preparation. These procedures had no effect on the activity of the high activity milks. Recombination experiments, whereby the milk serum from a low activity milk was added to the milk fat of a high activity milk and vice versa, and also kinetic studies suggest that the differences in activities between the two groups result from differences in availability of the enzyme and are independent of the source of milk fat.

Mit Hilfe der Elektrophorese und des Koagulationsbandes nach Weltmann werden die Einflusse von ultravioletten Strahlen auf die Eiweiskorper des mit der Ultrazentrifuge gewonnenen Milchserums untersucht. Dabei zeigen sich unter Versuchsbedingungen, die mit denen der Praxis der Milchbestrahlung vergleichbar sind, Veranderungen an den Proteinen. Diese Veranderungen treten jedoch fruhestens bei Bestrahlungszeiten von 20 sec Dauer auf und nehmen mit langerer Bestrahlungszeit zu. Sie dokumentieren sich elektrophoretisch bei kurzdauernder Bestrahlung in einer Abflachung der — in Analogie zum Blutserum so benannten — α- und β-Globulinfraktion, bei langdauernder Bestrahlung in einem Abflachen und Verbreitern auch der Albuminfraktion. Das γ-Globulin scheint selbst bei 60 min Belichtung unverandert. Mit Hilfe des Koagulationsbandes nach Weltmann wird auserdem eine Beeintrachtigung der Stabilitat der Milchserumproteine nach 40 sec Bestrahlung festgestellt. Die Versuchsbedingungen werden denen der Praxis gegenubergestellt und dabei die Schlusfolgerung gezogen, das die zur Rachitisprophylaxe ubliche Milchbestrahlung von 0,5 sec keinen mesbaren Einflus auf die Milchserumeiweiskorper ausuben durfte.