DAIRY CHEMISTRY AND BIOCHEMISTRY 0.16 0.14 0.12 0.04 0.02 Weeks of lactation Figure 5.2 Changes in the concentrations of calcium(----)and phosphorus (-)in bovine milk during lactation. 5.5.2 Stage of lactation a. an bv tation of total calcium is generally high both in early and late The concen station but in the intervening period no relation with stage of lactation is evident(Figure 5.2), Phosphorus shows a general tendency to increase as lactation advances(Figure 5. 2). The concentrations of colloidal calcium and inorganic phosphorus are at a minimum in early and at a maximum in late lactation milk. The concentrations of sodium and chloride( Figure 5.3)are high at the beginning of lactation, followed by a rapid decrease, then increase gradually until near the end of lactation when rapid increases occur The concentration of potassium decreases gradually throughout lactation The concentration of citrate which has a marked influence on the distribu tion of calcium, shows a strong seasonal variation(Figure 5.4), influenced more by feed than the stage of lactation. The ph of milk shows a strong
244 DAIRY CHEMISTRY AND BIOCHEMISTRY 0.18 - 0.16- 0.14 - 0.12 - 0.1- a 6 & G 0.08- 0.06 - p ...d ...*.. , .o,. ... . .. * .... ....*O"' 9.. o"..*....* ,... * ... *... , , . , , .*. .... I.1.0 .I..*.. = = - ~ - Weeks of lactation Figure 5.2 Changes in the concentrations of calcium (----) and phosphorus (-) in bovine milk during lactation. 5.5.2 Stage of lactation The concentration of total calcium is generally high both in early and late lactation but in the intervening period no relation with stage of lactation is evident (Figure 5.2). Phosphorus shows a general tendency to increase as lactation advances (Figure 5.2). The concentrations of colloidal calcium and inorganic phosphorus are at a minimum in early and at a maximum in late lactation milk. The concentrations of sodium and chloride (Figure 5.3) are high at the beginning of lactation, followed by a rapid decrease, then increase gradually until near the end of lactation when rapid increases occur. The concentration of potassium decreases gradually throughout lactation. The concentration of citrate, which has a marked influence on the distribution of calcium, shows a strong seasonal variation (Figure 5.4), influenced more by feed than the stage of lactation. The pH of milk shows a strong
SALTS OF MILK 245 Percent of lactation Figure 5.3 Changes in the concentration of chloride in bovine milk during lactation Figure 5. 4 Seasonality of the concentration of citric acid in bo
SALTS OF MILK 245 0.25 0.2 0.15 3 2 u ct 0.1 0.05 Percent of lactation Figure 5.3 Changes in the concentration of chloride in bovine milk during lactation. Monih Figure 5.4 Seasonality of the concentration of citric acid in bovine milk
DAIRY CHEMISTRY AND BIOCHEMISTRY seasonal trend: the ph of colostrum is about 6 but increases to the normal value of about 6 6-6. 7 shortly after parturition and changes little until late lactation, when the ph raises to as high as 7. 2, i.e. approaches that of blood (pH 7. 4)due to degeneration of the mammary cell membrane. The pH of milk also increases during mastitic infection(e.g 6.8-6.9), due to the influx of constituents from blood Figure 5.5 Correlations between the concentration of sodium and potassium(a) and sodium and chloride(b)in bovine milk
246 DAIRY CHEMISTRY AND BIOCHEMISTRY seasonal trend; the pH of colostrum is about 6 but increases to the normal value of about 6.6-6.7 shortly after parturition and changes little until late lactation, when the pH raises to as high as 7.2, i.e. approaches that of blood (pH 7.4) due to degeneration of the mammary cell membrane. The pH of milk also increases during mastitic infection (e.g. 6.8-6.9), due to the influx of constituents from blood. X Figure 5.5 Correlations between the concentration of sodium and potassium (a) and sodium and chloride (b) in bovine milk
SALTS OF MILK 247 5.5.3 Infection of the udder Milk from cows with mastitic infections contains a low level of total solids, especially lactose, and high levels of sodium and chloride, the concentration of which are directly related(Figure 5.5). The sodium and chloride ions come from the blood to compensate osmotically for the depressed lactose synthesis or vice versa These are related by the Koestler number Koestler number= 100×%Cl which is normally 1.5-3.0 but increases on mastitic infection and has been used as an index of such(better methods are now available, e.g. somatic cell count, activity of certain enzymes, especially catalase and N-acetyl glucosamidase). The pH of milk increases to approach that of blood during mastitic infection 5.5.4 Feed Feed has relatively little effect on the concentration of most elements in milk because the skeleton acts as a reservoir of minerals. the level of citrate in milk decreases on diets very deficient in roughage and results in the ' Utrecht phenomenon, i.e. milk of very low heat stability. Relatively small changes in the concentrations of milk salts, especially of Ca, Pi and citrate, can have very significant effects on the processing characteristics of milk and hence these can be altered by the level and type of feed, but definitive studies or his are lacking 5.6 Interrelations of milk salt constituents Various milk salts are interrelated and the interrelationships are affected by H Table 5.3). Those constituents, the concentrations of which are related to ph in the same way, are also directly related to each other(e.g. the concentrations of total soluble calcium and ionized calcium), while those related to pH in opposite ways are inversely related(e. g. the concentrations of potassium and sodium Relationships between some of the more important ions/molecules are shown in Figure 5.6. Three correlations are noteworthy: The concentration of lactose is inversely related to the concentration of soluble salts expressed as osmolarity. This results from the requirement that milk be isotonic with blood
SALTS OF MILK 247 5.5.3 Infection of the udder Milk from cows with mastitic infections contains a low level of total solids, especially lactose, and high levels of sodium and chloride, the concentration of which are directly related (Figure 5.5). The sodium and chloride ions come from the blood to compensate osmotically for the depressed lactose synthesis or vice versa. These are related by the Koestler number: 100 x %C1 %lactose Koestler number = which is normally 1.5-3.0 but increases on mastitic infection and has been used as an index of such (better methods are now available, e.g. somatic cell count, activity of certain enzymes, especially catalase and N-acetylglucosamidase). The pH of milk increases to approach that of blood during mastitic infection. 5.5.4 Feed Feed has relatively little effect on the concentration of most elements in milk because the skeleton acts as a reservoir of minerals. The level of citrate in milk decreases on diets very deficient in roughage and results in the ‘Utrecht phenomenon’, i.e. milk of very low heat stability. Relatively small changes in the concentrations of milk salts, especially of Ca, Pi and citrate, can have very significant effects on the processing characteristics of milk and hence these can be altered by the level and type of feed, but definitive studies on this are lacking. 5.6 Interrelations of milk salt constituents Various milk salts are interrelated and the interrelationships are affected by pH (Table 5.3). Those constituents, the concentrations of which are related to pH in the same way, are also directly related to each other (e.g. the concentrations of total soluble calcium and ionized calcium), while those related to pH in opposite ways are inversely related (e.g. the concentrations of potassium and sodium). Relationships between some of the more important ions/molecules are shown in Figure 5.6. Three correlations are noteworthy: 1. The concentration of lactose is inversely related to the concentration of soluble salts expressed as osmolarity. This results from the requirement that milk be isotonic with blood