Table 3.3 Composition of the phospholipids in milk from various species(expressed as mol of total lipid phosphorus) Phosphatidyl- Phosphatidyl- Phosphatidyl- Phosphatidyl Lysophospho- Species ethane inositol Sphingomyelin .0 34 3.3 357 3.2 11.0 Rabbit 249 04 Mink 6.6 153 8.3 fat globule membrane phospholipids
Table 3.3 Composition of the phospholipids in milk from various species (expressed as mol YO of total lipid phosphorus) Phosphatidyl- Phosphatidyl- Phosphatidyl- Phosphatidyl- LysophosphoSpecies choline ethanolamine serine inositol Sphingomyelin lipids“ cow Sheep Buffalo Goat Camel Ass Pig Human Cat Rat Guinea-pig Rabbit Mouse‘ Mink 34.5 29.2 27.8 25.7 24.0 26.3 21.6 27.9 25.8 38.0 35.7 32.6 32.8 52.8 31.8 36.0 29.6 33.2 35.9 32.1 36.8 25.9 22.0 31.6 38.0 30.0 39.8 10.0 3.1 3.1 3.9 6.9 4.9 3.1 3.4 5.8 2.7 3.2 3.2 5.2 10.8 3.6 4.1 3.4 4.2 5Ab 5.9 3.8 3.3 4.2 7.8b 4.9 7.1b 5.8’ 3.6 6.6 25.2 28.3 32.1 21.9 28.3 34.1 34.9 31.1 31.9 19.2 11.0 24.9 12.5 15.3 0.8 2.4 0.5 1 .o 5.1 3.4 3.1 2.0 0.4 8.3 “Mainly lysophosphatidylcholine but also lysophosphatidylethanolamine. bAlso contains lysophosphatidylethanolamine. ‘Analysis of milk fat globule membrane phospholipids. From Christie (1995)
MILK LIPIDS Table 3.4 Total fat and phospholipid content of some milk products Total lipid Phospholipids Phospholipid Product (%,w/) % w/w. of total lipid Whole milk Cream 03-04 0.16-0.29 002-008 Skim milk Buttermilk 003-0.18 the presence of proportionately larger amounts of membrane material in ese products. Cholesterol(Appendix 3C)is the principal sterol in milk(>95% of total sterols); the level (-0.3%, w/w, of total lipids) is low compared with many other foods. Most of the cholesterol is in the free form with less than 10% holesteryl esters. Several other sterols, including steroid hormones, oc at trace levels Several hydrocarbons occur in milk in trace amounts. Of these, caro tenoids are the most significant. In quantitative terms, carotenes occur at only trace levels in milk (typically -200 ugl) but they contribute 10-50% of the vitamin A activity in milk(Table 3.5)and are responsible for the yellow colour of milk fat. The carotenoid content of milk varies with breed (milk from Channel Island breeds contains 2-3 times as much carotene as milk from other breeds) and very markedly with season (Figure 3. 4 ). The latter reflects differences in the carotenoid content of the diet(since they are totally derived from the diet); fresh pasture, especially if is rich in clover and alfalfa, is much richer in carotenoids than hay of silage(due to oxidation on conservation) or cereal-based concentrates. The higher the carotenoid content of the diet, the more yellow will be the colour of milk and milk fat, e.g. butter from cows on pasture is yellower than that Table 3.5 Vitamin A activity and B-carotene in milk of different breeds of cows Channel Island breeds Non-Channel island breeds Winte Retinol (ul 1 Contribution (%)of β carotene to vitamin a ctivity Modified from Cremin and Power(1985)
MILK LIPIDS 73 Table 3.4 Total fat and phospholipid content of some milk products Total lipid Phospholipids Phospholipid as Product (%. WIV) (%, WIV) YO, w/w, of total lipids Whole milk 3-5 Cream 10-50 Butter 81-82 Butter oil - 100 Skim milk 0.03-0.1 Buttermilk 2 0.02-0.04 0.6- 1 .O 0.07-0. I8 0.3-0.4 0.14-0.25 0.16-0.29 0.02-0.08 0.02-0.08 0.01-0.06 17-30 0.03 -0.18 10 the presence of proportionately larger amounts of membrane material in these products. Cholesterol (Appendix 3C) is the principal sterol in milk (> 95% of total sterols); the level (-O.3%, w/w, of total lipids) is low compared with many other foods. Most of the cholesterol is in the free form, with less than 10% as cholesteryl esters. Several other sterols, including steroid hormones, occur at trace levels. Several hydrocarbons occur in milk in trace amounts. Of these, carotenoids are the most significant. In quantitative terms, carotenes occur at only trace levels in milk (typically -2OOpg1-') but they contribute 10-50% of the vitamin A activity in milk (Table 3.5) and are responsible for the yellow colour of milk fat. The carotenoid content of milk varies with breed (milk from Channel Island breeds contains 2-3 times as much p-carotene as milk from other breeds) and very markedly with season (Figure 3.4). The latter reflects differences in the carotenoid content of the diet (since they are totally derived from the diet); fresh pasture, especially if it is rich in clover and alfalfa, is much richer in carotenoids than hay or silage (due to oxidation on conservation) or cereal-based concentrates. The higher the carotenoid content of the diet, the more yellow will be the colour of milk and milk fat, e.g. butter from cows on pasture is yellower than that Table 3.5 Vitamin A activity and P-carotene in milk of different breeds of cows ~ ~ ~ ~~ ~~~~~ Channel Island breeds Non-Channel Island breeds Summer Winter Summer Winter Retinol (pl 1- ') 649 265 619 412 j-Carotene (pl I-') 1143 266 315 105 Retinollb-carotene ratio 0.6 11.0 2.0 4.0 Contribution (%) of 46.8 33.4 20.3 11.4 p-carotene to vitamin A activity Modified from Cremin and Power (1985)
DAIRY CHEMISTRY AND BIOCHEMISTRY _8 S 0 N D <5 EE三 Figure 3, 4 Seasonal variations in the concentration of B-carotene(O)and of vitamins A(A), D(O)and E(O)in milk and milk products(from Cremin and Power, 1985) from cows on winter feed, especially if the pasture is rich in clover (New Zealand butter is more yellow than Irish butter which in turn is more yellow than mainland European or Us butter). Sheep and goats do not transfer carotenoids to their milks which are, consequently, much whiter than bovine butter, cream, ice-cream)made from bovine milk in regions where goats'or sheep,'s milk is traditional (the carotenoids may be bleached by using
4 P e,w gih rnE Ob -. "I - Vitamin A (mg/100 g butter) -3 Y Tocopherol (&g fat) '< -. P 2. 2 Carotene (pg/100 ml milk) Vitamin D (IUA milk) P
MILK LIPIDS peroxides, e. g. H2O2 or benzoyl peroxide, or masked, e.g. with chlorophyll or titanium oxide Milk contains significant concentrations of fat-soluble vitamins(Table 3.5, Figure 3. 4)and milk and dairy products make a significant contribution to the dietary requirements for these vitamins in Western countries. The actual form of the fat-soluble vitamins in milk appears to be uncertain and their concentration varies widely with breed of animal, feed and stage of lactation, e.g. the vitamin A activity of colostrum is c. 30 times higher than that of mature milk Several prostaglandins occur in milk but it is not known whether they play a physiological role; they may not survive storage and processing in a biologically active form. Human milk contains prostaglandins E and F at concentrations 100-fold higher than human plasma and these may have a hysiological function, e.g. gut motility. 3.4 Fatty acid profile of milk lipids Milk fats, especially ruminant fats, contain a very wide range of fatty acids more than 400 and 184 distinct acids have been detected in bovine and human milk fats, respectively( Christie, 1995). However, the vast majority of these occur at only trace concentrations. The concentrations of the principal fatty acids in milk fats from a range of species are shown in table 3.6 Notable features of the fatty acid profiles of milk lipids include 1. Ruminant milk fats contain a high level of butanoic acid (C4: o)and other short-chain fatty acids. The method of expressing the results in table 3. 6 (% w/w)under-represents the proportion of short-chain acids-if ex- pressed as mol % butanoic acid represents c. 10% of all fatty acids(up to 15% in some samples), i. e. there could be a butyrate residue in c. 30% of all triglyceride molecules. The high concentration of butyric(butanoic) acid in ruminant milk fats arises from the direct incorporation of B-hydroxybutyrate (which is produced by micro-organisms in the rumen from carbohydrate and transported via the blood to the mammary gland where it is reduced to butanoic acid). Non-ruminant milk fats contain no butanoic or other short-chain acids the low concentrations of butyrate in milk fats of some monkeys and the brown bear require confirmation The concentration of butanoic acid in milk fat is the principle of the of butter with other fats i.e. Reichert Meissl and Polenski numbers which are measures of the volatile water-soluble and volatile water- insoluble fatty acids, respectively Short-chain fatty acids have strong, characteristic flavours and aromas. When these acids are released by the action of lipases in milk or
MILK LIPIDS 75 peroxides, e.g. H,O, or benzoyl peroxide, or masked, e.g. with chlorophyll or titanium oxide). Milk contains significant concentrations of fat-soluble vitamins (Table 3.5, Figure 3.4) and milk and dairy products make a significant contribution to the dietary requirements for these vitamins in Western countries. The actual form of the fat-soluble vitamins in milk appears to be uncertain and their concentration varies widely with breed of animal, feed and stage of lactation, e.g. the vitamin A activity of colostrum is c. 30 times higher than that of mature milk. Several prostaglandins occur in milk but it is not known whether they play a physiological role; they may not survive storage and processing in a biologically active form. Human milk contains prostaglandins E and F at concentrations 100-fold higher than human plasma and these may have a physiological function, e.g. gut motility. 3.4 Fatty acid profile of milk lipids Milk fats, especially ruminant fats, contain a very wide range of fatty acids: more than 400 and 184 distinct acids have been detected in bovine and human milk fats, respectively (Christie, 1995). However, the vast majority of these occur at only trace concentrations. The concentrations of the principal fatty acids in milk fats from a range of species are shown in Table 3.6. Notable features of the fatty acid profiles of milk lipids include: 1. Ruminant milk fats contain a high level of butanoic acid (C4:o) and other short-chain fatty acids. The method of expressing the results in Table 3.6 (Yo, w/w) under-represents the proportion of short-chain acids - if expressed as mol %, butanoic acid represents c. 10% of all fatty acids (up to 15% in some samples), i.e. there could be a butyrate residue in c. 30% of all triglyceride molecules. The high concentration of butyric (butanoic) acid in ruminant milk fats arises from the direct incorporation of P-hydroxybutyrate (which is produced by micro-organisms in the rumen from carbohydrate and transported via the blood to the mammary gland where it is reduced to butanoic acid). Non-ruminant milk fats contain no butanoic or other short-chain acids; the low concentrations of butyrate in milk fats of some monkeys and the brown bear require confirmation. The concentration of butanoic acid in milk fat is the principle of the widely used criterion for the detection and quantitation of adulteration of butter with other fats, i.e. Reichert Meissl and Polenski numbers, which are measures of the volatile water-soluble and volatile waterinsoluble fatty acids, respectively. Short-chain fatty acids have strong, characteristic flavours and aromas. When these acids are released by the action of lipases in milk or
Table 3.6 Principal fatty acids (wt of total)in milk triacylglycerols or total lipids from various species Species 4:06:08:010:012:014:016:016:118:018:118:218:3C20-C22 331.61,330 8336 29.8 2.6 fusk-Ox 081119 uck antelop 74 mean of six 04 4.222.737.6 emur macaco Horse 14912 4032 6567 T--T-T-T 1,1 Guinea-pig 313 1125 123623 1.1 Cottontail rabbit 9487 09 0.6 3.5 Pygmy sperm whale Polar bear ephant a ---TT T 18.5 04 2.7 6.4 5.6 From Christie(1995)
Table 3.6 Principal fatty acids (wt YO of total) in milk triacylglycerols or total lipids from various species Species 4:O 6:O 8:O 1O:O 12:O 14:O 16:O 16.1 18:O 18.1 18:2 18:3 C,,-C2, cow Buffalo Sheep Goat Dall-sheep Moose Blackbuck antelope Elephant Human Monkey (mean of six species Baboon Lemur macaco Horse Pig Rat Guinea-pig Marmoset Rabbit Cottontail rabbit European hare Mink Chinchilla Red kangaroo Platypus Numbat Bottle-nosed dolphin Manatee Pygmy sperm whale Harp seal Northern elephant seal Polar bear Grizzly bear Musk-ox 1.6 1.6 2.8 2.9 0.9 0.3 T 6.0 T 0.6 0.4 T - - - - T T T - - - - - - - - - - - - T T 1.3 1.1 2.7 2.7 1.9 0.2 8.4 2.7 0.3 T 5.9 5.1 0.2 1.8 1.1 - - - 22.4 9.6 10.9 - - - ~ - - 0.6 - - - - - 3 .O 1.9 9.0 8.4 4.7 4.9 5.5 6.5 29.4 1.3 11.0 7.9 1.9 5.1 0.7 7.0 8.0 20.1 14.3 17.7 - - - - - - 3.5 - - - T - 3.1 2.0 5.4 3.3 2.3 1.8 0.6 3.5 18.3 3.1 4.4 2.3 10.5 6.2 0.5 7.5 8.5 2.9 3.8 5.5 0.5 T 0.1 0.1 0.3 4.0 - - - - - 0.5 0.1 9.5 8.7 11.8 10.3 6.2 10.6 2.0 11.5 5.3 5.1 2.8 1.3 15.0 5.7 4.0 8.2 2.6 7.7 1.7 2.0 5.3 3.3 3.0 2.7 1.6 0.9 3.2 6.3 3.6 5.3 2.6 3.9 2.1 26.3 2.3 30.4 3.4 25.4 3.4 24.6 2.2 19.5 1.7 23.0 2.4 28.4 4.3 39.3 5.7 12.6 3 .O 20.2 5.7 21.4 6.7 16.5 1.2 27.1 9.6 23.8 7.8 32.9 11.3 22.6 1.9 31.3 2.4 18.1 5.5 14.2 2.0 18.7 1 .o 24.8 5.0 26.1 5.2 30.0 - 31.2 6.8 19.8 13.9 14.1 3.4 21.1 13.3 20.2 11.6 27.6 9.1 13.6 17.4 14.2 5.7 18.5 16.8 16.4 3.2 14.6 10.1 9.0 12.5 23.0 15.5 4.5 5.5 0.5 5.9 4.9 4.2 1 .o 2.3 3.5 6.5 2.9 3.4 3.8 3.0 2.9 10.9 6.3 3.9 7.0 3.3 0.5 7.4 4.9 3.6 13.9 20.4 - 29.8 28.7 20.0 28.5 27.2 23.1 21.2 19.2 17.3 46.4 26.0 22.7 25.7 20.9 35.2 26.7 33.6 29.6 13.6 12.7 14.4 36.1 35.2 37.2 22.7 57.7 23.1 47.0 46.6 21.5 41.6 30.1 30.2 2.4 2.5 2.1 2.2 2.1 4.0 20.2 3.3 3.0 13.0 14.5 37.6 6.6 14.9 11.9 16.3 18.4 10.9 14.0 24.7 10.6 14.9 26.8 10.4 5.4 7.9 1.2 1.8 0.6 1.2 1.9 1.2 5.6 0.8 2.5 1.4 3.0 4.1 3.7 0.7 1.4 1.3 0.6 0.5 12.6 0.7 0.8 5.7 0.9 4.4 9.8 1.7 1.5 2.9 2.1 7.6 0.1 0.2 2.2 0.6 0.9 0.4 2.3 - - - T T - - 0.4 2.6 - - - T - - - - - 1.1 T 7.0 T 0.4 T - - 0.1 12.2 0.2 17.3 0.4 4.5 31.2 29.3 11.3 9.5 From Christie (1995)