Soluble Milk Proteins Research Articles

The Nature of the Ingested Protein Has No Effect on Lean Body Mass During Energy Restriction in Overweight Rats

Severe energy restriction in obesity not only leads to fat mass loss but also to lean mass loss. The aim of this study was to compare the capacity of casein, a slowly digested protein, and milk soluble proteins (MSP; rapidly digested) to limit the loss of lean mass induced by energy restriction. Obesity was first induced in male Wistar rats by a 5-week feeding with a high-fat high-sucrose diet. The impact of energy restriction was then studied with high-protein (32%) diets containing either casein, MSP, or a 50/50 mixture of both proteins for 3 weeks (n = 10 per group). Food intake, body weight, nitrogen balance, creatinine, and 3-methyl-histidine excretion were measured during energy restriction. Then, tissue weights, plasma metabolic parameters (amino acids, glucose, insulin, cholesterol, triglycerides), and in vivo liver and extensor digitorum longus (EDL) muscle protein synthesis rates were measured in postabsorptive state at the end of the experimental period. Although significant differences relevant to protein metabolism were observed between groups (protein intake, plasma amino acid concentrations, fecal nitrogen excretion, muscle protein synthesis rates), week per week, there were no significant differences in nitrogen balance whatever the protein used. In conclusion, our results show that in young overweight energy restricted rats, using a high-protein diet, the nature of protein intake has no influence on body protein retention.

The composition of interfacial material from skim milk foams

The foaming properties of skim milk vary with temperature of foaming in the range from 5 to 85°C, with foams of maximum stability being formed at approximately 45°C. This paper reports the significance of different milk fractions in the foam and concludes that the micellar casein fraction plays an important role in stabilization of milk foam formed at higher temperatures. This finding was supported by the fact that added calcium chloride increased and calcium-chelating agents decreased foam stability. These effects were attributed to the increase and decrease, respectively, in the amount of micellar casein in the milk. Furthermore, bubble ghost material sedimented by low-speed centrifugation of foam was found to contain predominantly caseins, and electron micrographs of foams formed at 45°C clearly showed casein micelles spread over the interface. However, other structures observed in the electron micrographs suggest that soluble milk proteins and possibly polar lipids are also present in the foams and play a role in formation of milk foams.

Once-daily milking effects in high-yielding Alpine dairy goats

Two experiments were conducted to determine the milk loss of high-yielding Alpine goats resulting from once-daily milking (ODM) and its relationship to udder cisternal size. We investigated the effects of application of this management strategy on milk yield, composition, and technological parameters: lipolysis, fat globule size, and cheese yield. In a second experiment, we investigated the effect of repeated periods of ODM management during lactation. Goats at the beginning of both experiments were at 25 d in milk on average and were previously milked twice daily (twice-daily milking; TDM). In experiment 1, which was conducted for 2 periods (P) of 9 wk (P1, P2), 48 goats were grouped (1, 2, 3, and 4) according to milk yield, parity, and somatic cell count (SCC). Over the 2 periods, goats from group 1 were managed with TDM and those from group 2 were managed with ODM. In group 3, goats were assigned to TDM during P1 and ODM during P2, conversely, those in group 4 were assigned to ODM in P1 and TDM in P2. During P1, the 12 goats from group 3 underwent 2 distinct morning machine milkings to measure milk repartition (cisternal and alveolar) in the udder based on the “atosiban method.” On P1 plus the P2 period of 18 wk, milk loss caused by ODM (compared with TDM) was 16%. In our condition of 24-h milk accumulation, there was no correlation between milk loss and udder cisternal size. Milk fat content, fat globule size, or apparent laboratory cheese yield was not modified by ODM, but milk protein content (+2.7g/kg), casein (+1.8g/kg), milk soluble protein concentration (+1.0g/kg), and SCC increased, whereas lipolysis decreased (−0.3mEq/100g of oleic acid). In experiment 2, which was conducted for 4 periods (P1, P2, P3, P4) of 5 wk each, 8 goats, blocked into 2 homogenous groups (5 and 6), were used to study the effects of a double inversion of milking frequency (TDM or ODM) for 20 wk of lactation. Milk loss was 17% and ODM did not modify milk fat or protein contents, SCC, casein, or milk soluble protein concentration, but lipolysis was decreased (−0.3mEq/100g of oleic acid). Neither experiment showed the effects of period of ODM management on milk yield, milk fat or protein content, SCC, fat globule size, lipolysis, casein, milk soluble protein concentration, or apparent laboratory cheese yield.

Immobilization of alkaline serine endopeptidase from Bacillus licheniformis on SBA-15 and MCF by surface covalent binding

An industrial enzyme, alkaline serine endopeptidase, was immobilized on surface modified SBA-15 and MCF materials by amide bond formation using carbodiimide as a coupling agent. The specific activities of free enzyme and enzyme immobilized on SBA-15 and MCF were studied using casein (soluble milk protein) as a substrate. The highest activity of free enzyme was obtained at pH 9.5 while this value shifted to pH 10 for SBA-15 and MCF immobilized enzyme. The highest activity of immobilized enzymes was obtained at higher temperature (60 °C) than that of the free enzyme (55 °C). Kinetic parameters, Michaelis–Menten constant ( K m) and maximum reaction velocity ( V max), were calculated as K m = 13.375, 11.956, and 8.698 × 10 −4 mg/ml and V max = 0.156, 0.163 and 0.17 × 10 −3 U/mg for the free enzyme and enzyme immobilized on SBA-15 and MCF, respectively. The reusability of immobilized enzyme showed 80% of the activity retained even after 15 cycles. Large pore sized MCF immobilized enzyme was found to be more promising than the SBA-15 immobilized enzyme due to the availability of larger pores of MCF, which offer facile diffusion of substrate and product molecules.

When given in a rapidly absorbed form, a protein meal favors the splanchnic extraction and metabolism of dietary N at the expense of its peripheral uptake and anabolic use

Though we recently showed that, compared to casein, soluble milk protein were more extracted in the splanchnic bed but contributed less to peripheral protein accretion, the specific influence of the absorption kinetics of dietary protein, independently of their amino acid (AA) profile, on their further anabolism in individual tissues remains unknown. Clinical experiment was coupled with compartmental modeling to investigate the postprandial utilization of proteins of similar composition: intact (CA) and hydrolyzed (CH) casein. Experimental data were obtained in intestine, blood and urine for meal nitrogen (Nm) kinetics after a 15N‐labeled CA or CH meal and analyzed using a 13‐compartment model to predict the cascade of Nm absorption, transfer and regional metabolism. Compared to CA, CH had a similar whole‐body postprandial retention of Nm, but a faster rate of absorption, resulting in earlier and stronger hyperaminoacidemia and hyperinsulinemia. The faster kinetics of Nm absorption after CH favored both its catabolic (+25%) and anabolic (+40%) utilization in the splanchnic bed and lowered its further peripheral availability, which felt from 22% to 13% of the dietary N absorbed. The kinetics of dietary AA delivery thus constituted an independent factor of modulation of their regional metabolism in the postprandial phase, a fast supply favoring the splanchnic Nm uptake over its peripheral anabolic use.

Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement

The in vivo quality of milk protein fractions has seldom been studied in humans. Our objective was to compare the postprandial utilization of dietary nitrogen from 3 [(15)N]-labeled milk products: micellar caseins (MC), milk soluble protein isolate (MSPI), and total milk protein (TMP). The macronutrient intakes of 23 healthy volunteers were standardized for 1 wk, after which time the subjects ingested a meal containing MC (n = 8), MSPI (n = 7), or TMP (n = 8). [(15)N] was measured for an 8-h period in plasma amino acids, proteins, and urea and in urinary urea. The transfer of dietary nitrogen to urea occurred earlier after MSPI ingestion than after MC and TMP ingestion, and concentrations remained high for 8 h, concomitantly with higher but transient hyperaminoacidemia and a higher incorporation of dietary nitrogen into plasma amino acids. In contrast, deamination, postprandial hyperaminoacidemia, and the incorporation of dietary nitrogen into plasma amino acids were lower in the MC and TMP groups. Finally, total postprandial deamination values were 18.5 +/- 2.9%, 21.1 +/- 2.8%, and 28.2 +/- 2.9% of ingested nitrogen in the TMP, MC, and MSPI groups, respectively. Our results confirm the major role of kinetics in dietary nitrogen postprandial utilization and highlight the paradox of MSPI, which, despite its high Protein Digestibility Corrected Amino Acid Score, ensures a rate of amino acid delivery that is too rapid to sustain the anabolic requirement during the postprandial period. Milk proteins had the best nutritional quality, which suggested a synergistic effect between soluble proteins and caseins.

The fast, soluble milk protein stimulate the splanchnic, but not the peripheral metabolism of meal nitrogen as compared to casein in humans

In the postprandial phase, soluble milk protein are more oxidized than casein due to their faster delivery from the gut, but the other impacts on the splanchnic and peripheral metabolism of a fast vs slow amino acid supply remain unclear. Clinical experiment was coupled with compartmental modeling in order to investigate the postprandial utilization of three 15N-labeled milk products: total milk protein (microfiltered milk, MF), micellar caseins (CAS) and milk soluble protein isolate (MSPI). Experimental data for the meal nitrogen (Nm) postprandial kinetics in blood and urine were obtained in healthy adults fed a single meal containing MSPI, CAS or MF after a prior 7d standardization of the diet (1.3 g.kg−1.d−1 of protein). These data were then analyzed using a 12-compartment model that allowed to predict the cascade of Nm ingestion, absorption, splanchnic uptake for both catabolic and anabolic purposes and further peripheral availability and anabolic use. As shown in the table above, compared to MF, CAS was slow and WPSI was fast according to the rate of their absorption. The fastest protein (WPSI) stimulated both the oxidative and anabolic metabolic pathways in the splanchnic bed, while the slowest protein (CAS) induced the highest peripheral protein accretion.

Heat Markers and Quality Indexes of Industrially Heat-Treated [15N] Milk Protein Measured in Rats

To determine the bioavailability of industrially heat-treated milk proteins, male Wistar rats were given [15N]-labeled meals containing either nonheated-micellar casein (CAS), milk soluble protein isolate (MSPI), and microfiltered milk (MF)-or heated products-"high temperature short time" pasteurized (HTST), "higher temperature, shorter time" pasteurized (HHST), ultrahigh temperature-treated (UHT), and spray-dried (SPRAY) milks. The postprandial distribution of dietary nitrogen was measured in the splanchnic area and urea. Digestibility was around 96% except for SPRAY (94%) and MSPI (98%). Ingested nitrogen recovered in the splanchnic bed was 19.3% for SPRAY, 16.7% for MF, and around 14-15% for other products. Deamination of dietary nitrogen reached 21.2, 20.6, and 18.2% of ingested nitrogen for MSPI, SPRAY, and CAS, respectively, and around 14-16% for other products. In our model, only spray drying led to a significant increase of splanchnic extraction. Moreover, the biological value of purified protein fractions appeared to be lower than that seen in products containing total milk protein.

Effects of skimmed milk powder, whey or casein on tissue trace element status and antioxidant enzyme activities in rats fed control and copper-deficient diets

Results from a number of studies have suggested that milk-based diets are particularly effective at inducing copper (Cu) deficiency. In the current study, groups (n=5) of weanling Wistar rats were provided with control (14.4 mg Cu/kg diet) and Cu-deficient (1.1 mg Cu/kg diet) diets containing skimmed milk powder (SMP; 385 g/kg), whey (270 g/kg) or casein (103 g/kg) and deionised water for 91 days after which they were exsanguinated and the liver and heart removed. Tissue Cu levels, copper-zinc superoxide dismutase (CuZnSOD) and cytochrome c oxidase activities were significantly (P<0.05) lower in control animals fed SMP compared with those fed casein. Animals fed whey exhibited intermediate values for these indices of Cu status. Although hepatic iron levels were significantly (P<0.05) lower in animals fed the SMP diet, hepatic zinc was significantly (P<0.05) higher as were the hepatic activities of glutathione reductase and the selenium-dependent glutathione peroxidase. There were no significant differences, however, in hepatic levels of thiobarbituric acid reactive substances (TBARS) among any of the experimental groups. It is proposed that these changes in tissue trace elements and enzyme activities may be related to dietary interactions involving casein and soluble milk proteins.

Serum albumin secretion in rat milk.

1. The concentration of serum albumin in rat milk, rat serum, the stomach contents of suckling rats and mammary homogenates has been measured. 2. Serum albumin in expressed milk ranges in concentration between 3.5 and 6 mg/ml and amounts to an average of 4-5 mg/100 mg total protein whereas, in the stomach contents of suckling rats, serum albumin was 3.2 mg/100 mg total protein. 3. Corresponding concentrations of a second soluble milk protein, alpha-lactalbumin, were 2.9 mg/100 mg total protein in the milk and 1.2 mg/100 mg total protein in the stomach contents. 4. Serum albumin is a major protein in mammary homogenates at 10 mg/100 mg total soluble protein and the calculated total mammary pool of albumin amounts to 110 mg/rat. 5. There was a significant negative correlation between the serum albumin concentration and the ratio of potassium to sodium ions in milk samples obtained from rats milked with varying oxytocin treatments. 6. No evidence for albumin mRNA could be detected when mammary total RNA was probed with a complementary DNA (cDNA) for rat albumin. 7. The data are consistent with albumin being a major whey protein in the rat, it being synthesized at an extramammary site and transferred to the milk space by a paracellular mechanism from an extravascular mammary pool rather than directly from the serum.

Ca 125 and Ca 19-9: two cancer-associated sialylsaccharide antigens on a mucus glycoprotein from human milk.

The cancer-associated antigens Ca 125 and Ca 19-9 were demonstrated by radioimmunoassay to form structural units of a mucus glycoprotein in human milk taken from healthy women four days after parturition. The glycoprotein precipitated with the casein fraction at pH 4.6 and was completely absent in the whey as judged from Ca 19-9 assay. It could be effectively enriched by phenol-saline extraction from soluble milk proteins and further purified by gel filtration on Sephacryl S300 and Sephacryl S400. The active component with a bouyant density of 1.41 g/ml in isopycnic density gradient centrifugation (CsCl) shared common physico-chemical and chemical characteristics of mucus glycoproteins. Carbohydrates representing about 68% by weight were conjugated to protein by alkali-labile linkages, exclusively and were essentially free of D-mannose. Activities of Ca 125 and Ca 19-9 were both destroyed by treatment with periodate, mild alkali or neuraminidase suggesting the antigens are sialylated saccharides bound to protein by alkali-labile linkages. The fraction of monosialylated saccharide alditols isolated after reductive beta-elimination from the mucus glycoprotein was shown to inhibit monoclonal antibodies anti-(Ca 125) and anti-(Ca 19-9) in radioimmunoassay.

Behavior of Enteropathogenic Escherichia coli in Camembert Cheese Made From Ultrafiltered Milk

ABSTRACTSkimmilk retentates from ultrafiltration (UF) were used in combination with concentrated cream (67% milk fat) to prepare a liquid precheese mixture that with the addition of rennet, lactic starter culture and a mold spore preparation of Penicillium candidum was transformed readily into Camembert cheese upon ripening. Yield increases from the retention of soluble milk protein, closer weight control tolerances for individual cheeses and reduction in rennet in comparison to the conventional Camembert process were observed. The behavior of enteropathogenic E. coli (ECC) serotypes was demonstrated in the Camembert cheese made from UF processes. Relationships were determined in UF Camembert as to microbial type and numbers used to inoculate the precheese, and as to site of survival and growth of different EEC serotypes. Differences which were observed in the physicochemical properties between conventional and UF cheesemilk mixtures predisposed the UF Camembert cheeses to greater E. coli survival and growth than in the Camembert cheeses made conventionally.

Urinary Nitrogen and Vitamin E Status of Calves Fed Heat-Denatured Soluble Milk Proteins

Twenty male Holstein calves were assigned at 3 days of age across four dietary treatments. Treatments were whole milk and milk with 25%, 50%, and 75% of the soluble protein denatured. All diets were fed at 10% of body weight for 10 wk. Three 5-day nitrogen balance trials were conducted during the experiment. Chopped wheat straw was fed ad lib. Several basic nitrogenous compounds and zinc excretion were measured in urine samples. Packed cell volume and in vitro erythrocyte hemolysis were measured on whole blood samples. Vitamin E was measured on samples of plasma. Denatured proteins failed to change body weights, nitrogen balance, nitrogen retained, or nitrogen digested. All amounts of denatured protein increased packed cell volumes. Hemolysis of erythrocytes and vitamin E in plasma were not changed. Vitamin E in plasma was low. Denatured protein decreased daily excretion of urinary zinc. Denatured protein did not increase urinary excretion of 3-methylhistidine, but it did decrease urinary excretion of 1-methylhistidine and increased an “unknown 4”. Heat-denatured proteins had an effect on mineral metabolism and on nitrogen metabolism through excretion of a specific basic nitrogenous compound.

29. The Effect of Heat upon the Rennin Coagulation. II

1. Clean milk has been “flash” pasteurised at 165°F. Portions of the same raw milk have been treated with small amounts respectively of starter culture and lactic acid, so as to raise the acidity, before being similarly pasteurised.2. Comparison of the whey obtained by rennetting the three raw portions has shown that those from the acidified milk contained more soluble protein than the original.3. The differences between the raw and pasteurised milk in their coagulation time with rennin have been found to be proportionately much greater in the acidified portions.4. These differences in coagulation time have been shown to be correlated with decreases in the amount of soluble protein found in. the whey separated from the coagulum.5. These experimental results, together with those of other investigators, have been made the basis of a suggestion that the decreased coagulability of heated milk with rennin is partly due to flocculation of soluble milk protein upon the casein micelles.

Pasteurised Milk for Cheddar Cheese-Making. I: A Preliminary Chemical Investigation

Summary1. With a view to a chemical study of the ripening of cheese made from raw and from pasteurised milk, two sets of three loaf Cheddar cheese were made from clean milk and from market milk respectively, so that in each set there was one cheese made from raw milk, one from milk flash-pasteurised at 165° F., and one from milk flash-pasteurised at 185° F.2. Analyses of the whey drawn from each cheese showed a tendency, especially with market milk of lower hygienic quality, for pasteurisation to cause more of the soluble milk proteins to be incorporated in the cheese.3. When acidity developed rapidly in the whey after cutting, the resulting cheese was depleted of a proportion of its mineral constituents.4. The cheese made from pasteurised milk developed a bitter flavour, which was very pronounced in those made from the milk heated to the higher temperature.5. The chemical analyses showed that in both sets, pasteurisation reduced the quantity of ultimate decomposition products which were formed during the process of ripening.The experiments recorded here were carried out at the National Institute for Research in Dairying, Shinfield, Reading. The author desires to express his appreciation of the facilities which have been placed at his disposal and of the interest that has been taken in the work by various members of the staff, in particular by Miss D. V. Dearden (who was responsible for the making of the cheese), Capt. J. Golding, and Dr R. Stenhouse Williams. Acknowledgment is also due to Prof. Wm Riddet, Dairy Research Institute, New Zealand, who suggested the desirability of an investigation of this nature.