《乳品生物化学》（英文版） 3 Milk lipids

3 Milk lipids 3.1 Introduction The milks of all mammals contain lipids but the concentration varies widely between species from c. 2% to greater than 50%(Table 3. 1). The principal function of dietary lipids is to serve as a source of energy for the neonate and the fat content in milk largely reflects the energy requirements of the species, e.g. land animals indigenous to cold environments and marine mammals secrete high levels of lipids in their milks Milk lipids are also important 1. as a source of essential fatty acids (i.e. fatty acids which cannot be synthesized by higher animals, especially linoleic acid, C18: 2) and fat soluble vitamins(A, D, E, K); and 2. for the favour and rheological properties of dairy products and foods in which they are used Because of its wide range of fatty acids, the favour of milk fat is superior to that of other fats. In certain products and after certain processes, fatty acids serve as precursors of very flavourful compounds such as methyl ketones and lactones. Unfortunately, lipids also serve as precursors of compounds Table 3. 1 The fat content of milks from various species (g1-) Species Fat content S Fat conter Marmoset Musk-ox 32-206 Mink ed kangaroo Lemurs g From Christie(1995)

3 Milk lipids 3.1 Introduction The milks of all mammals contain lipids but the concentration varies widely between species from c. 2% to greater than 50% (Table 3.1). The principal function of dietary lipids is to serve as a source of energy for the neonate and the fat content in milk largely reflects the energy requirements of the species, e.g. land animals indigenous to cold environments and marine mammals secrete high levels of lipids in their milks. Milk lipids are also important: 1. as a source of essential fatty acids (i.e. fatty acids which cannot be synthesized by higher animals, especially linoleic acid, &) and fat￾soluble vitamins (A, D, E, K); and 2. for the flavour and rheological properties of dairy products and foods in which they are used. Because of its wide range of fatty acids, the flavour of milk fat is superior to that of other fats. In certain products and after certain processes, fatty acids serve as precursors of very flavourful compounds such as methyl ketones and lactones. Unfortunately, lipids also serve as precursors of compounds Table 3.1 The fat content of milks from various species (g I-') Species Fat content Species Fat content cow Buffalo Sheep Goat Dall-sheep Moose Antelope Elephant Human Horse Monkeys Lemurs Pig Musk-ox 33-47 47 40-99 41 -45 109 32-206 39-105 93 85-190 38 19 10-51 8-33 68 Marmoset Rabbit Guinea-pig Snowshoe hare Muskrat Mink Chinchilla Rat Red kangaroo Dolphin Manatee Pygmy sperm whale Harp seal Bear (four species) 77 183 39 71 110 134 117 103 9-119 62-330 55-215 502- 5 32 108-331 153 From Christie (1995)

DAIRY CHEMISTRY AND BIOCHEMISTRY that cause off-flavour defects(hydrolytic and oxidative rancidity) and as solvents for compounds in the environment which may cause off-flavour For many years, the economic value of milk was based mainly or totally on its fat content, which is still true in some cases. This practice was satisfactory when milk was used mainly or solely for butter production Possibly, the origin of paying for milk on the basis of its fat content, apart from its value for butter production, lies in the fact that relatively simple quantitative analytical methods were developed for fat earlier than for protein or lactose. Because of its economic value, there has long been commercial pressure to increase the yield of milk fat per cow by nutritional or genetic means. To facilitate the reader, the nomenclature, structure and properties of t principal fatty acids and of the principal lipid classes are summarized in Appendices 3A, 3B and 3C. The structure and properties of the fat-soluble vitamins, A, D, E and K, are discussed in Chapter 6 3.2 Factors that affect the fat content of bovine milk Bovine milk typically contains c. 3.5% fat but the level varies widely, depending on several factors, including: breed, individuality of the animal, stage of lactation, season, nutritional status, type of feed, health and age of the animal, interval between milkings and the point during milking when the sample is taken Of the common European breeds, milk from Jersey cows contains the ighest level of fat and that from Holstein/ Friesians the lowest( Figure 3.1 The data in Figure 3.1 also show the very wide range of fat content in individual-cow samples The fat content of milk decreases during the first 4-6 weeks after parturition and then increases steadily throughout the remainder of lacta- tion,especially toward the end( Figure 3. 2). For any particular population, fat content is highest in winter and lowest in summer, due partly to the effect of environmental temperature. Production of creamery(manufacturing) milk in Ireland, New Zealand and parts of Australia is very seasonal lactational, seasonal and possibly nutritional effects coincide, leading to large seasonal changes in the fat content of milk(Figure 3. 3), and also in he levels of protein and lactose For any individual animal, fat content decreases slightly dr success- ive lactations, by c. 0.2% over a typical productive lifetime(about five lactations). In practice, this factor usually has no overall effect on the fat content of a bulk milk supply because herds normally include cows of various ages. the concentration of fat (and of all other milk-specific constituents)decreases markedly on mastitic infection due to impaired

68 DAIRY CHEMISTRY AND BIOCHEMISTRY that cause off-flavour defects (hydrolytic and oxidative rancidity) and as solvents for compounds in the environment which may cause off-flavours. For many years, the economic value of milk was based mainly or totally on its fat content, which is still true in some cases. This practice was satisfactory when milk was used mainly or solely for butter production. Possibly, the origin of paying for milk on the basis of its fat content, apart from its value for butter production, lies in the fact that relatively simple quantitative analytical methods were developed for fat earlier than for protein or lactose. Because of its economic value, there has long been commercial pressure to increase the yield of milk fat per cow by nutritional or genetic means. To facilitate the reader, the nomenclature, structure and properties of the principal fatty acids and of the principal lipid classes are summarized in Appendices 3A, 3B and 3C. The structure and properties of the fat-soluble vitamins, A, D, E and K, are discussed in Chapter 6. 3.2 Factors that affect the fat content of bovine milk Bovine milk typically contains c. 3.5% fat but the level varies widely, depending on several factors. including: breed, individuality of the animal, stage of lactation, season, nutritional status, type of feed, health and age of the animal, interval between milkings and the point during milking when the sample is taken. Of the common European breeds, milk from Jersey cows contains the highest level of fat and that from Holstein/Friesians the lowest (Figure 3.1). The data in Figure 3.1 also show the very wide range of fat content in individual-cow samples. The fat content of milk decreases during the first 4-6 weeks after parturition and then increases steadily throughout the remainder of lacta￾tion, especially toward the end (Figure 3.2). For any particular population, fat content is highest in winter and lowest in summer, due partly to the effect of environmental temperature. Production of creamery (manufacturing) milk in Ireland, New Zealand and parts of Australia is very seasonal; lactational, seasonal and possibly nutritional effects coincide, leading to large seasonal changes in the fat content of milk (Figure 3.3), and also in the levels of protein and lactose. For any individual animal, fat content decreases slightly during success￾ive lactations, by c. 0.2% over a typical productive lifetime (about five lactations). In practice, this factor usually has no overall effect on the fat content of a bulk milk supply because herds normally include cows of various ages. The concentration of fat (and of all other milk-specific constituents) decreases markedly on mastitic infection due to impaired

MILK LIPIDS Holstein Ayrshire Figure 3. 1 Range of fat content in the milk of individual cows of four breeds( from Jenness and Patton, 1959) synthesizing ability of the mammary tissue; the effect is clear-cut in the case of clinical mastitis but is less so for subclinical infection Milk yield is reduced by underfeeding but the concentration of fat usuall increases, with little effect on the amount of fat produced. Diets low in roughage have a marked depressing effect on the fat content of milk, with little effect on milk yield. Ruminants synthesize milk fat mainly from carbohydrate-derived precursors; addition of fat to the diet usually cause slight increases in the yield of both milk and fat, with little effect on fat content of milk. Feeding of some fish oils (e.g. cod liver oil, in an effort to ease the concentrations of vitamins A and d in milk) has a very marked (c. 25%)depressing effect on the fat content of milk, apparently due to the high level of polyunsaturated fatty acids( the effect is eliminated by hydr genation), although oils from some fish species do not cause this effect

I MILK LIPIDS 35 - 30 - B f - 25- 0 % 3 - S s 20- r 0 15- 2 10 - 5- 69 Percentage fat Figure 3.1 Range of fat content in the milk of individual cows of four breeds (from Jenness and Patton, 1959). synthesizing ability of the mammary tissue; the effect is clear-cut in the case of clinical mastitis but is less so for subclinical infection. Milk yield is reduced by underfeeding but the concentration of fat usually increases, with little effect on the amount of fat produced. Diets low in roughage have a marked depressing effect on the fat content of milk, with little effect on milk yield. Ruminants synthesize milk fat mainly from carbohydrate-derived precursors; addition of fat to the diet usually causes slight increases in the yield of both milk and fat, with little effect on fat content of milk. Feeding of some fish oils (e.g. cod liver oil, in an effort to increase the concentrations of vitamins A and D in milk) has a very marked (c. 25%) depressing effect on the fat content of milk, apparently due to the high level of polyunsaturated fatty acids (the effect is eliminated by hydro￾genation), although oils from some fish species do not cause this effect

DAIRY CHEMISTRY AND BIOCHEMISTRY 50 10 Week of lactation Figure 3.2 Typical changes in the concentrations of fat(O), protein() and lactose(O)in bovine milk during lactation 4.6 兰E8 3.4 S O N D Ire 3.3 Seaso in the fat content of bovine milk in some Eu s(●, United Kingdom(口, france, Germany(△), reland(▲) om an foras tal 1981)

70 DAIRY CHEMISTRY AND BIOCHEMISTRY 5.0 - 0 L. 2 4.0 3.0 0 10 20 30 40 50 Week of lactation Figure 3.2 Typical changes in the concentrations of fat (O), protein (m) and bovine milk during lactation. 4.6 - 4.4 - 4.2 - 4.0 - 3.8 - 3.6 - 3.4 - lactose (0) in JFMAMJJASOND Month Figure 3.3 Seasonal changes in the fat content of bovine milk in some European countries: (Denmark (O), Netherlands (O), United Kingdom (O), France (U), Germany (A), Ireland (A) (From An Foras Taluntais, 1981.)

MILK LIPIDS The quarters of a cows udder are anatomically separate and secrete milk of markedly different composition. The fat content of milk increas s continu ously throughout the milking process while the concentrations of the partially trapped in the alveoli and their passage is hinde co ppear to be various non-fat constituents show no change; fat globules a cow Is incompletely milked, the fat content of the milk obtained at that milking will be reduced; the trapped 'fat will be expressed at the subsequent milking, giving an artificially high value for fat content If the intervals between milkings are unequal (as they usually are in commercial farming), the yield of milk is higher and its fat content lower after the longer interval; the content of non-fat solids is not infuenced by milking interval 3.3 Classes of lipids in milk Triacylglycerols(triglycerides) represent 97-98% of the total lipids in the milks of most species(Table 3. 2). The diglycerides probably represent incompletely synthesized lipids in most cases, although the value for the ra probably also includes partially hydrolysed triglycerides, as indicated by the high concentration of free fatty acids, suggesting damage to the milk fat globule membrane (MFGM) during milking and storage. The very high level of phospholipids in mink milk probably indicates the presence of mammary cell membranes Although phospholipids represent less than 1% of total lipid, they play a particularly important role, being present mainly in the MFGM and other membraneous material in milk. The principal phospholipids are phos- phatidylcholine, phosphatidylethanolamine and sphingomyelin(Table 3. 3) Trace amounts of other polar lipids, including ceramides, cerobrosides and gangliosides, are also present. Phospholipids represent a considerable pro- portion of the total lipid of buttermilk and skim milk(table 3. 4), reflecting acids 3.2 Composition of individual simple lipids and total phospholipids in milks of some Lipid class Bufalo Human Rat Mink 986 98.2 875 81.3 Free fatty acids 00270 Phospholipids 0.5 0.26 16 07 15.3 From Christie(1995). T, Trace

MILK LIPIDS 71 The quarters of a cow’s udder are anatomically separate and secrete milk of markedly different composition. The fat content of milk increases continu￾ously throughout the milking process while the concentrations of the various non-fat constituents show no change; fat globules appear to be partially trapped in the alveoli and their passage is hindered. If a cow is incompletely milked, the fat content of the milk obtained at that milking will be reduced; the ‘trapped’ fat will be expressed at the subsequent milking, giving an artificially high value for fat content. If the intervals between milkings are unequal (as they usually are in commercial farming), the yield of milk is higher and its fat content lower after the longer interval; the content of non-fat solids is not influenced by milking interval. 3.3 Classes of lipids in milk Triacylglycerols (triglycerides) represent 97-98% of the total lipids in the milks of most species (Table 3.2). The diglycerides probably represent incompletely synthesized lipids in most cases, although the value for the rat probably also includes partially hydrolysed triglycerides, as indicated by the high concentration of free fatty acids, suggesting damage to the milk fat globule membrane (MFGM) during milking and storage. The very high level of phospholipids in mink milk probably indicates the presence of mammary cell membranes. Although phospholipids represent less than 1% of total lipid, they play a particularly important role, being present mainly in the MFGM and other membraneous material in milk. The principal phospholipids are phos￾phatidylcholine, phosphatidylethanolamine and sphingomyelin (Table 3.3). Trace amounts of other polar lipids, including ceramides, cerobrosides and gangliosides, are also present. Phospholipids represent a considerable pro￾portion of the total lipid of buttermilk and skim milk (Table 3.4), reflecting Table 3.2 species (weight YO of the total lipids) Composition of individual simple lipids and total phospholipids in milks of some Lipid class Triacylgl ycerols Diacylglycerols Monoacylgl ycerols Cholesteryl esters Cholesterol Free fatty acids Phospholipids cow Buffalo Human Pig Rat Mink 97.5 0.36 0.027 T 0.31 0.027 0.6 98.6 98.2 0.7 T 0.1 T 0.3 0.25 0.5 0.4 0.5 0.26 96.8 0.7 0.1 0.06 0.6 0.2 1.6 87.5 2.9 0.4 1.6 3.1 0.7 - 81.3 1.7 T T T 1.3 15.3 From Christie (1995). T, Trace

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- Lysophospho￾Species 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, caro￾tenoids 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 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 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 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

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)