Milk Citrate Research Articles

Feed and Animal Factors Influencing Milk Fat Composition

Genetic selection for increased milk fat percentage leads to increased proportions of short-chain fatty acids in milk fat and decreased proportions of long-chain fatty acids. Milk fat composition is strongly influenced by stage of lactation; proportion of short chains (de novo synthesis) is low initially and increases until at least 8 to 10 wk into lactation. Milk fat composition is changed more by the amount and composition of dietary fat than any other dietary component. Seasonal and regional differences in milk fat composition are measurable, most likely because of local differences in feed supplies.Milk fat composition can be modified readily by changing the feeding regimen. The most significant changes in milk fat quality relate to rheological (melting) properties, which influence numerous aspects of character and quality of manufactured dairy products. Dietary fat fed to change milk fat composition may also influence contents of protein, urea, citrate, and soluble calcium in milk and influence oxidative stability and flavor. It is important for both dairy nutritionists and dairy food chemists to understand the consequences of feeding programs on milk quality.

Calcium, phosphate and citrate in human milk at initiation of lactation.

The onset of copious milk secretion (lactogenesis II) in women occurs between 1 and 3 d after birth, and during this period the composition of breast milk changes. During the first 5 d of lactation we measured the concentrations of total, diffusible and ionized Ca (Catot, Cad, Ca2+), diffusible phosphate (Pid), diffusible citrate (Citd) and lactose in the breast milk. On day 1 after birth the concentrations (mean +/- SEM) were Catot, 5.71 +/- 0.30 mM; Cad, 2.66 +/- 0.19 mM; Ca2+, 2.90 +/- 0.18 mM; Pid, 0.26 +/- 0.16 mM; Citd, 0.25 +/- 0.03 mM and lactose, 76 +/- 11 mM. Between day 1 and day 4 the concentration of Catot increased 1.7-fold to 9.56 +/- 0.39 mM, Cad increased 1.8-fold to 4.75 +/- 0.26 mM, Ca2+ decreased by 20% to 2.33 +/- 0.13 mM, Pid increased 6.6-fold to 1.69 +/- 0.11 mM, Citd increased 20-fold to 5.06 +/- 0.21 mM, and lactose increased 2.3-fold to 173 +/- 4 mM. A high correlation has been found between [Cad] and [Citd] in the milk of both ruminant and non-ruminant species, which show a wide range in concentrations of [Cad] and [Citd], and the data fit a simple physicochemical model of ion equilibria in the aqueous phase of milk. The results of the present study confirm the relationship between [Cad] and [Citd] in human milk, even during lactogenesis II when the composition of the milk is changing very rapidly.

Citrate metabolism in Lactococcus lactis subsp. lactis var. diacetylactis strains

AbstractThe formation of diacetyl, acetoin, 2,3‐butylene glycol, acetaldehyde, ethanol and lactic acid during 24 h of cultivation in milk with 0.19 and 0.5 % of citrate has been studied. Depending on the strain, bacteria produced 1.5 ‐ 1.9 mg of diacetyl, 212 ‐ 311 mg of acetoin and 137 ‐ 156 mg of butylene glycol in 1 1 milk. An increase of the citrate concentration in milk to 0.5 % resulted in an increase in the production of diacetyl from 58 to 74 % and of acetoin by 2.8 ‐ 3.7 times. The strains of distinct activity of acetoin reductase produced in these conditions 2.3 ‐ 2.7 times as much as 2,3‐butylene glycol. The recovery of citrate in the from of C4‐compounds ranged from 76 to 98 %, yet barely 0.18 ‐ 0.44 % in the from of diacetyl. Increased concentration of citrate in milk stimulated the production of diacetyl and acetaldehyde to the similar extent, thereby it did not result in the deterioration of organoleptic qualities of starters and milk products. Within the doses used citrate did not significantly affect growth and acidifying activity of the bacteria.

Milk Lactose, Citrate, and Glucose as Markers of Lactogenesis in Normal and Diabetic Women

A study was undertaken to define an appropriate marker of lactogenesis II (the onset of copious milk secretion) in mothers, and to determine the effect of diabetes on this marker. Changes in the concentrations of three milk components—lactose, citrate, and glucose—were measured in 38 normal mothers and 6 type I diabetic mothers up to 10 days after birth. Milk yield was measured in 12 of the normal mothers, and all mothers were asked to note the time of milk “coming in” (the feeling of overfullness of the breasts). The average concentrations of lactose, citrate, and glucose in milk were low for the first 24 h after birth, then between 24 and 48 h after birth there was a rapid increase in the concentrations of lactose and citrate, and this transitional period was followed by a plateau period that began between 60 and 84 h after birth. For individual mothers the transitional period for citrate began 32 ± 9 h (n = 13) and finished 77 ± 10 h (n = 17) after birth, and for lactose the transitional period finished at 53 ± 12 h (n = 29) after birth. For diabetic mothers these times were significantly later. The average 24‐h milk intake by infants increased from 82 to 556 ml/24 h between 24 and 144 h after birth. Milk intakes were correlated with the concentration of lactose (r = 0.52, n = 51, p < 0.001), citrate (r = 0.47, n = 47, p < 0.001), and glucose (r = 0.69, n = 50, p < 0.001). The time of milk “coming in” was highly variable (59 ± 13) (X ± SD) and occurred well after the onset of copious milk secretion between 24 and 48 h after birth. We conclude that for individual mothers, milk lactose and citrate are useful markers of lactogenesis II. The changes in the concentrations of these markers suggested that lactogenesis II was delayed in type I diabetic mothers.

Abnormal zinc content in human milk. Risk for development of nutritional zinc deficiency in infants.

An abnormally low concentration of zinc in mother's milk has been associated with clinical nutritional zinc deficiency in premature and term newborns. Defective mammary gland secretion of zinc was suggested as the causative factor. We investigated whether low milk zinc concentration might be reflected in an abnormality of the distribution of zinc between casein, whey, and fat components of the milk, in a reduction in the levels of milk citrate, a zinc-binding ligand, or in abnormal levels of copper and iron. Milk from mothers of four low-birth-weight infants was identified as being deficient in zinc content for the lactational stage. One infant had clinical signs of nutritional zinc deficiency. For two of the three infants with subclinical deficiencies in whom balance study data were available, the apparent zinc balance was negative (-5.7 and -6.0 mumol/kg per day). These milks were examined for content and distribution of zinc, copper, and iron, and citrate concentration. Although total zinc concentration (4.5 to 17.2 mumol/L) was below the 95% prediction interval (15.2 to 59.7 mumol/L) for the lactational stage, the distribution of zinc was normal between milk components. Levels of citrate (1.46 to 5.13 mmol/L) were also within normal limits, as were levels of copper (0.27 to 0.85 mumol/L and iron (0.41 to 1.13 mumol/L). We concluded that there was no indirect evidence of a secretory abnormality in milk zinc deficiency, but speculated that there might instead be an abnormality of zinc uptake by the mammary gland from the plasma.

Coprecipitation modulates the solubility of minerals in bovine milk

The solubilities of zinc, iron, copper, magnesium, calcium, inorganic phosphate, and citrate in milk decreased when acidic milk preparations were neutralized. In decaseinated bovine milk soluble zinc, iron, and copper were reduced 90%, 60%, and 50%, respectively, as the pH was raised from 4 to 7. Simultaneous precipitation of minerals and citrate was confirmed by analysis of washed precipitate. We propose that the diminished solubilities of zinc, iron, copper, magnesium, and citrate are linked to the precipitation of calcium phosphate through one or more mechanisms of coprecipitation. Such control on mineral solubility may have an impact upon mineral absorption from milk.

Seasonal changes in the fat composition and concentration of citrate and related metabolites in cows' milk

SUMMARYSeasonal variations were observed in the proportion of long-chain (C18and over) and medium-chain (C6–14) fatty acids (FA) in milk fat. Long-chain FA were proportionately higher during the period June to October. Changes were also observed in the concentrations of citrate, isocitrate and 2-oxoglutarate in milk. Changes in [isocitrate]: [2-oxoglutarate] correlated positively with changes in the proportion of long-chain FA in milk fat and negatively with the proportion of medium-chain FA.

SOME PROPERTIES OF SOURED AND DE-ACIDIFIED BUFFALO'S MILK ? MINERAL COMPOSITION

The influence of passing electric current in the acidic buffalo milk with a view to explore the possibility of retaining and utilizing such milk for the manufacture of dairy products was studied. Twelve trials were conducted on de-acidification of milk and the quality of milk was judged by the Heat Coagulation time and the concentration of major minerals, namely, calcium, magnesium, phosphate and citrate in normal buffalo milk, its rennet whey, acidic milk whey and the de-acidified milk whey. The average HCT for normal milk, acidic milk and de-acidic milk was 42.66 ± 1.40, 2.74 ± 0.03, 44.41 ± 1.78 min, respectively. The average pH of these milks were 6.72 ± 0.19, 6.21 ± 0.02 and 6.77 ± 0.03, respectively. The soluble calcium, in different types of whey obtained from whole milk, acidic milk and de-acidified milk were 24.03%, 33.11% and 21.37%, respectively. Similarly, magnesium contents were 56.78%, 66.58% and 56.61% and the phosphate contents were 43.87%, 60.74% and 42.24%; and citrate 67.93%, 81.48% and 62.16%.

Effect of ACTH and oxytocin treatment on lactoferrin and citrate in cows' milk.

Six dairy cows were treated before milkings with either oxytocin (Pitocin, 20 i.u.) or ACTH (Synacthen, 150 i.u.), principally to determine their effect on the ratio of citrate: lactoferrin concentrations in the milk. With ACTH treatment, after 3 d milk yield and citrate concentration decreased significantly, lactoferrin and bovine serum albumin (BSA) concentrations increased significantly. Somatic cell counts (SCC) increased temporarily in the milk of three of the cows which previously had greater than 100 000 cells/ml. Lactoferrin yield remained fairly constant but citrate yield was significantly reduced. The citrate: lactoferrin molar ratio decreased from 1373 to 606. With oxytocin treatment, after 4 d milk yield first increased and then significantly decreased, citrate concentration decreased significantly while there were no significant changes in lactoferrin or BSA concentration or in the yield of any other milk constituents. The citrate: lactoferrin molar ratio decreased from 1621 to 1301. There were no significant changes in SCC either during treatment or 4 d after treatment but there was a significant rise at 16 d after treatment. It was concluded that in lactating cows both hormones affected citrate and lactoferrin concentrations in the direction that would improve the antibacterial properties of milk, but that this was accompanied by adverse effects on milk secretion. The extent of the change was not sufficient to be likely to produce inhibition of coliform bacteria.

Effects of genetic variants of κ-casein and β-lactoglobulin on cheesemaking

SUMMARYThe effects of κ-casein and β-lactoglobulin (β-lg) genetic variants on cheesemaking were examined in two laboratory scale experiments. Variants of κ-casein had highly significant (P < 0·001) effects on milk citrate content (A > B) and rennet clotting time (A > B). When curds were cut at constant firmness there were only minor effects of κ-casein variants on milk component recoveries and cheese yield and composition. A tendency to higher fat recoveries from milks containing κ-casein B was reflected in significantly (P < 0·05) higher fat contents in cheese after 3·5 months of ripening. Genetic variants of βlg had highly significant (P < 0·001) effects on casein number (B > AB > A) and protein recoveries (B > AB > A) and significant (P < 0·05) effects on yield of cheese dry matter (B > AB > A). Green (unripened) cheeses made from the different milks also differed in fat, protein and moisture contents, probably in part due to differences in fat/casein ratios of the cheesemilks. The compositional differences were reflected in differences in the extent of proteolysis during ripening (A > AB > B). In the experiment with β-lg genetic variants the effect of time of cold storage of the cheesemilk was also investigated. No differences were found in milk composition and component recoveries or cheese yield, composition and quality when milks were cold-stored for 24, 48 or 120 h before cheesemaking.

Caprine mammary differentiation and initiation of lactation following prepartum colchicine infusion

1. 1. Milk from both colchicine-infused and uninfused udder halves had similar levels of somatic cells, serum albumin, pH, citrate, and lactose throughout the experimental period. 2. 2. Milk citrate and lactose concentrations gradually increased in both colchicine-infused and uninfused udder halves during early lactation while levels of somatic cells and serum albumin decreased as lactation progressed. 3. 3. No differences in parenchymal development or cytological differentiation were observed between colchicine-treated and untreated mammary tissue obtained prepartum, at parturition, or 7 days postpartum. 4. 4. Colchicine-infused udder halves produced about 9% less milk than uninfused controls during the first 30 days of lactation.

Computer Calculation of Zinc(II)-Complex Distribution in Milk

Computer simulations were performed to determine the distribution of zinc among some potentially important low-molecular-weight ligands (citrate, glutamate and picolinate) in both human and bovine milk. At high concentrations of picolinate, this ligand forms a neutral complex, which may facilitate intestinal absorption of the metal, but at lower levels of picolinate, zinc-citrate complexes are the predominant low-molecular-weight species.milk zinc bioavailability citrate glutamate picolinate

Changes in milk citrate concentration during lactation in the goat.

Changes in milk citrate concentration during lactation in the goat.

Some effects of acute fasting and climatic stresses upon milk secretion in friesland sheep

1. 1. Five lactating Friesland sheep were exposed to control conditions and to the stresses of fasting for 24 hr, a hot (40°C) environmental temperature for 48 hr, and a cold (1°C) temperature for 48 hr. 2. 2. Between 17 and 24 hr after withdrawal of food, milk secretion rate was not significantly reduced, but milk osmolality and the concentration of citrate in milk were reduced. 3. 3. In the hot environment, rectal temperature averaged 1.7°C above normal. After 24 to 48 hr of exposure, milk secretion rate was not significantly reduced but milk osmolality, total nitrogen concentration and potassium concentration were reduced, and in milk fat 16-carbon fatty acid was less prevalent and 18-carbon fatty acids more prevalent. Mean plasma prolactin concentration was high during heat exposure but individual results were very variable. lti]4. In the cold environment, total oxygen consumption averaged 2.2 ml · kg −1 · min −1 above normal. After 24 to 48 hr of exposure, milk secretion was reduced, the concentration of total nitrogen increased and the prevalence of short-chain fatty acids in milk fat also increased. Mean plasma prolactin concentration was low during cold exposure but, again, individual results were variable. 4. 5. These effects have been compared with those previously reported in other high-yielding species.

Inorganic constituents of milk: I. Correlation of soluble calcium with citrate in bovine milk.

A high correlation was found between soluble calcium and citrate concentrations during a study of seasonal changes in the composition of the commercial milk supply to South-west Scotland. A simple physicochemical model of the ion equilibria in the aqueous phase of milk suggests that the observed correlation is causal. This hypothesis was corroborated by an analysis of data on individual cow milks and by experiments involving the addition of citrate to milk at constant pH.

The secretion of citrate into milk.

1. The time course of changes in specific activities of citrate, lactose and fatty acids in milk during frequent milking, following the I.V. administration of labelled glucose, acetate and chylomicrons in goats has been studied. Peak specific activities of lactose and citrate in milk were reached at 2-3 hr, while peak specific activites of fatty acids were reached at 5-7 hr. 2. Following short I.A. infusions of 24Na, 36Cl, and 42K, peak specific activities in milk were reached in 1 hr or less. 3. The mammary epithelium of lactating goats was found to be virtually impermeable to labelled citrate in both directions. 4. Labelled citrate had an apparent volume of distribution in lactating guinea-pigs mammary slices in vitro similar to that of extracellular space markers. 5. Treatment of goats with large doses of oxytocin markedly increased the permeability of the secretory epithelium to labelled citrate. 6. In the goat mammary gland, citrate, protein and calcium failed to enter milk which had been diluted with isosmotic lactose by intraductal injection, whereas Na, K and Cl did enter, thus tending to restore the concentrations of these ions to normal. 7. It is suggested that citrate, which is formed within the sucretory cell, enters milk not by passage across the apical cell membrane but, in common with lactose and milk protein, by exocytosis of Golgi vesicles. It appears that citrate is held at high concentrations in milk by virtue of the impermeability of the mammary epithelium to the forms in which it occurs in milk.

Citrate in milk: a harbinger of lactogenesis.

CONSIDERABLE amounts of citrate (130–160 mg per 100 ml) occur in the milk of cows and goats, and approximately half this amount in that of women. In spite of its central role in the metabolism of all cells, the significance of the presence of citrate in milk and its mode of secretion are not known1. We report that the final stage of lactogenesis is preceded by the onset of citrate secretion into colostrum.

Calculation of the intracellular distribution of acetyl CoA and CoA, based on the use of citrate synthase as an equilibrium enzyme

Knowledge of the acetyl CoA/CoA ratio of the cytosolic and mitochondrial compartments of the cell is important in the understanding of control mechanisms in carbohydrate and lipid metabolism. The relative amounts of acetyl CoA and free CoA have been implicated in the control of pyruvate dehydrogenase [ 1, 21, pyruvate carboxylase [3], pyruvate kinase [4] and citrate cleavage enzyme [S, 61 while recent studies by Pontremoli [7] have shown effect of free CoA on fructose diphosphatase activity. There have been two major approaches to examining the problem of the compartmentation of CoA derivatives. Firstly, the relative impermeability of the mitochondrial inner membrane to CoA derivatives has permitted the direct fractionation of tissues such as liver and the determination of the distribution of acetyl CoA, CoA and long chain acyl CoA compounds [8]. Secondly, attempts have been made to derive the acetyl CoA/CoA ratio of the mitochondrial compartment by use of the calculated intracellular distribution of citrate and oxaloacetate and by the assumption that citrate synthetase was functioning as an equilibrium enzyme [9]. Clearly, both methods have certain disadvantages, the former because of the possibility that the ratio of acetyl CoA/CoA alters during the fractionation procedure and the latter because of the basic assumption of citrate synthase equilibrium, a point of some controversy [ 11 and see also 1, IO] as well as the assumptions used in arriving at the mitochondrial citrate and oxaloacetate [ 12, 131. A direct experimental approach to the mitochondrial acetyl CoA/CoA ratio can be made using ruminant mammary tissue..This tissue has an extremely low citrate cleavage enzyme. Thus, glucose can readily give rise to mitochondrial acetyl CoA and mitochondrial and cytosolic citrate (as shown by the incorporation of glucose carbons into milk citrate [ 141) but does not form cytosolic acetyl CoA (as shown by the lack of incorporation of glucose carbon into fatty acids [ 151). It therefore follows that, if ruminant mammary tissue slices are incubated with glucose as sole substrate and the metabolite profile determined, it is probable that virtually the whole of the acetyl CoA determined will be located within the mitochondria. Fractionation studies can then be used to obtain the distribution of the (acetyl CoA + CoA) in the cytosol and mitochondria, while the distribution of citrate and oxaloacetate may be calculated by the methods previously established for liver [ 12, 131. From these data, the acetyl CoA/ CoA ratio in each of the cell compartments may be calculated. Using sheep mammary gland, evidence has been obtained for the close approximation of the Keq. and mass action ratio of citrate synthase which may be valuable in the further interpretation of pathways of metabolism in this tissue.

The metabolism of [U-14C]glucose, [1-14C]palmitic acid and [1-14C]stearic acid by the lactating mammary gland of the sow

Summary(1) Lactating Large White sows were given an intravenous infusion of [U-14C]glucose (3 sows), or of triglycerides containing [1-14C]palmitic acid (1 sow) or [1-14C]stearic acid (1 sow).(2) The contribution of labelled plasma constituents to the synthesis of milk citrate, lactose, triglyceride glycerol, individual amino acids of the milk proteins and individual fatty acids of the triglyceride fraction was estimated by the ‘transfer quotient’ method. For the glucose infusions the mean values for the transfer quotients were: lactose, 70%; citrate, 42%; glyceride glycerol, 38%; protein, 3%; laurate, 6%; myristate, 12%; palmitate, 6%; palmitoleate, 4% and stearate, 2%. Palmitic acid of the plasma triglycerides made similar contributions of about 60% to the palmitic and palmitoleic acids of milk fat, whereas stearic acid made a major contribution (71 %) to the stearic acid of milk fat but a smaller contribution (42%) to oleic acid.(3) The results are compared with corresponding values for the goat and the cow.

Utilization of milk citrate by lactic acid bacteria and ‘blowing’ of film-wrapped cheese

SummaryA study was made of the utilization of citrate in milk by some lactic acid bacteria. WhenStreptococcus diacetilactis1007 was grown alone or with eitherStreptococcus cremoris924 orLactobacillus caseiB 142/C or with both these latter organisms, > 99% of the milk citrate was utilized within 5 days.L. caseiB 142/C andL. casei/Str. cremorisutilized 57 and 14% of the citrate, respectively. WhenL. caseiC 2 andL. caseiC 5 were grown in milk in whichStr. cremoris924 had been previously grown, 94 and 64%, respectively, of the citrate was utilized after 7 days at 30°C.Cheeses were made using a citrate-fermenting and a non-citrate-fermenting starter and citrate concentrations of the milks, wheys and curds were determined during cheese-making. WithStr. cremoris924, citrate was preferentially retained in the curd at pressing, the concentration in the curd moisture being 2·9 times that in the whey. With the mixed starterStr. cremoris924/Str. diacetilactis1007, the curd at pressing and from the press contained only 27 and 5%, respectively, of the citrate present in theStr. cremoriscurd at these times.Cheeses were made usingStr. cremoris924, combinations ofStr. cremoris/Str. diacetilactis1007, or with δ-gluconic acid lactone instead of starter, with and without the addition ofL. caseiC 5, in order to examine the ability of the latter organism to produce ‘blowing’ in the sense of distension of the Cryovac wrapping of film-wrapped cheeses.L. caseiC 5 neither accelerated the decrease in cheese citrate nor produced blowing of the film-wrapping. Possible reasons for this behaviour are discussed.