Artyku³ przegl¹dowy Review
Growing health awareness is driving consumers to look for food products that have a beneficial effect on the human body. Functional food is gaining special importance. Pisulewski et al. (24) define functional food as food products containing nutrients that have desirable effects on physiological changes in the human body, leading to optimum health and reduced risk of lifestyle diseases.
According to the definition adopted by FUFOSE (Functional Food Science in Europe) in the consensus document (1999), a food can be regarded as functio-nal if it has been satisfactorily demonstrated to benefi-cially affect one or more target functions in the body beyond adequate nutritional effects in a way that is relevant to either an improved state of health and well-being and/or a reduction of the risk of disease. A func-tional food must remain food and it must demonstrate its effects in amounts that can normally be expected to be consumed in the diet (10, 29).
The fact that goat products have been classified as functional food due to their nutritive and dietetic value and thus health-promoting benefits calls for the
development of goat husbandry and breeding as well as for increasing the production of goat milk and meat. Goat milk is a valuable food product and excellent raw material from which products of high nutritive value and exquisite taste are made. It is one of the oldest human foods, as evidenced by oral traditions and records, including the Old Testament: And there will be goats milk enough for thy food, for the food of thy household; and maintenance for thy maidens. In Poland, goats are used in the direction of the milk. Two breeds of goats dominate in the country: the white (about 20% population) and the color (about 12%) improved. Also 11% of this is Saanen breed, 8% Alpine breed and 7.5% Karpacka breed. Currently important is the Boer (burska) breed, constituting about 38% of the population. It is a meat breed used in the stock of goats used to cross mark for correcting meat features.
Funcional ingredients of goat milk protein The high nutritive value of goat milk is associated with its chemical composition. Many studies (5-7, 13,
Health-promoting properties of goat milk
HENRYKA BERNACKADepartment of Small Ruminant Biology and Environmental Biochemistry, Faculty of Animal Breeding and Biology, University of Technology and Agriculture, ul. Mazowiecka 28, 85-084 Bydgoszcz, Poland
Bernacka H.
Health-promoting properties of goat milk
Summary
Goat milk is a valuable food product and excellent raw material from which products of high nutritive value and exquisite taste are made. Many studies showed that goat milk contains 2.9-3.8% of protein, 2.8-5.9% of fat, 4.1-4.9% of lactose and 11.5-13.6% of total solids on average. The higher digestibility and absorption of goat milk is mainly associated with the content of whey proteins. Whey proteins account for 0.6-0.7% of milk and show beneficial nutritive, physiological and functional properties. About 75% of all milk whey proteins are albumins, which include á-lactoalbumins and â-lactoglobulins, a rich source of bioactive peptides with extra physiological activity. Other whey proteins are lactoferrin, lactoperoxidase, immuno-globulins, glycomacropeptide, and various growth factors. The quality of fat is largely determined by the content of individual fatty acids. As is clear from numerous studies the profile of fatty acids is more beneficial in goat milk compared to sheep and bovine milk because of the UFA/SFA is the ratio 0.56, of 0.52 (sheep milk) vs. 0.37 (bovine milk). In addition, milk is a rich source of vitamins and minerals. The goat milk compared to bovine milk contains a similar amount of vitamin B6 and pantothenic acid, niacin more (about 3.5-fold) but less vitaminum B12 (about 4-fold), and folic acid (approximately 6-fold). In terms of mineral composition of goat milk compared to bovine milk, the former is richer in calcium, phosphorus, potassium and chlorine, and lower in sodium, sulfur, iron and copper. However, sheep milk is richer than the milk of goats and cows in both mineral compositions (except for potassium, manganese and copper) and vitamins (except vitamin A and biotin).
19, 23, 31, 33, 34) have showed that goat milk con-tains 2.9-3.8% of protein, 2.8-5.9% of fat, 4.1-4.9% of lactose and 11.5-13.6% of total solids on average. As is evident from the data in table 1, the chemical composition of goat milk is similar to cow milk, with the main difference in the protein and fat structure.
The richest source of functional milk components is protein. In human nutrition, it mainly serves the nutritional function as it provides non-essential amino acids and nitrogen for the synthesis of body proteins and amino acids (30). Goat milk proteins have a high value because they contain all non-essential amino acids. The content of non-essential amino acids varies according to the protein fraction. Whey proteins are rich mainly in lysine, threonine, isoleucine and valine. Alpha-lactoalbumin, with the highest biological value, has relatively large amounts of cystine and tryptophan. Casein in milk occurs as the precursor of caseino-gen. It is a complex heterogeneous protein. The main fractions are áS1, áS2, beta and kappa-casein. As shown by Belloni-Businco et al. (3), Pe³czyñska (22) and Squergin et al. (32), the proportion of casein in milk is estimated to be about 2.12% and constitutes 75-85% of all proteins (tab. 2). It was shown that about 60% of allergic reactions in humans are caused by the prin-cipal milk protein casein and lactoglobulin. The most allergenic is the casein fraction áS1, the content of which in goat milk is very small unlike in cow milk, in which it forms about 33% of all caseins. Krzy¿ewski et al. (14) report after Remeuf and Lenoir that 100 g of total casein contains 5.6 g of the áS1 fraction in goat milk compared to 38 g in cow milk. For this reason children with protein intolerance cannot consume cow milk due to the risk of allergic disorders.
Small amounts of the áS1 casein fraction and the small size of casein micelles cause goat milk to be rapidly digested by proteolytic enzymes of the stomach, as a result of which goat milk is also recommended for people with gastrointestinal problems, especially ulcerations. Kappa-casein was also shown to have antithrombotic properties as it inhibits platelet aggre-gation and serotonin secretion. Many bioactive pep-tides, released during enzymatic digestion, were iden-tified in sequences of casein (1, 15, 25).
The higher digestibility and absorption of goat milk is mainly associated with the content of whey proteins. Table 3 presents the composition and content of whey proteins in total whey proteins and in skimmed milk.
Whey proteins account for 0.6-0.7% of milk and show beneficial nutritive, physiological and functional properties. Unlike casein, they contain no phosphorus and are characterized by a high content of sulfur amino acids, mainly methionine and cystine. About 75% of all milk whey proteins are albumins, which include á-lactoalbumins and â-lactoglobulins, a rich source of bioactive peptides with extra physiological activity. Other whey proteins are lactoferrin, lacto-peroxidase, immunoglobulins, glycomacropeptide, and various growth factors.
One of the functional components of goat milk is alpha-lactoalbumin (á-LA). Forming about 21% of all proteins, it serves different functions in the body: it is a calcium carrier and it can bind other metals such as magnesium, cobalt and zinc. In addition, it acts as an s t n e n o p m o C Cow Sheep Goat Human s d il o S 12.3 18.2 13.2 12.4 t a F 3.4 7.1 4.0 3.8 n i e t o r p l a t o T n i e s a c : g n i d u l c n i x x x x x xxx wheyproteins 2 . 3 5 . 2 5 6 . 0 7 . 5 6 . 4 8 0 . 1 6 . 3 9 . 2 1 6 . 0 2 . 1 4 . 0 7 . 0 e s o t c a L 4.6 4.6 4.6 7.0 s l a r e n i M 0.7 0.9 0.8 0.2 ) g 0 0 1 /l a c k ( y g r e n E 66 97 70 63
Tab. 1. Chemical composition of ruminant and human milk (%) (19, 23, 34)
Tab. 2. Content and composition of casein in milk (3, 22, 32) s n o it c a rf n i e s a C Cow Sheep Goat n i e s a c l a t o t f o % a 1s a 2s 3133..09 42.9 1185..48 b 37.5 43.5 50.1 k 9.4 8.8 13.2 s r e h t O 6.2 4.8 2.5 ) % ( k li m n i t n e t n o c a 1s a 2s 00..8304 1.54 00..3394 b 0.91 1.56 1.06 k 0.23 0.32 0.28 s r e h t O 0.15 0.17 0.05 l a t o T 2.44 3.59 2.12
Tab. 3. Composition and content of whey proteins in total whey proteins and in skimmed milk (3, 22, 32)
n o it c a rf n i e t o r p y e h W Cow Goat Sheep s n i e t o r p y e h w l a t o t f o t n e c r e P al-actoalbumin 16.2 21.4 10.8 bl-actoglobuiln 59.3 54.2 61.1 n ir r e f o t c a L 19.5 12.8 18.1 s n il u b o l g o n u m m I 15.0 11.5 20.0 ) % ( k li m d e m m i k s n i t n e t n o C al-actoalbumin 0.11 0.13 0.12 bl-actoglobuiln 0.38 0.33 0.66 n ir r e f o t c a L 0.06 0.08 0.09 s n il u b o l g o n u m m I 0.10 0.07 0.21 l a t o T 0.65 0.61 1.08
immune factor (which is particularly important in infant feeding) and has an anti-cancer effect (9, 25).
Another whey protein with func-tional properties is beta-lactoglobulin (â-LG). It forms the largest part of all whey proteins in milk (54%). Because
of a high methionine content, â-LG provides protec-tion against cancer development. It is a carrier of retinol, which is essential for the normal development of infants and for the vision process. Other functions performed by beta-lactoglobulin in the body are the ability to bind fatty acids, as well as antioxidant properties (by binding Cu and Fe ions, it inhibits the oxidation of milk fat). It must be remembered, how-ever, that beta-lactoglobulin is an antigenic protein and can therefore induce allergy (this protein is not found in a womans milk) (9, 25).
Lactoferrins (Lf) are a group of biologically active milk proteins with functional properties. Lactoferrin shows a high affinity to Fe, especially one of the forms known as hololactoferrin. It is characterized by high thermal stability in both acid and neutral environments. It also takes part in the transport of Ca, Cu, Mn, Zn and Al. Because of its antioxidant properties, it pre-vents the formation of free radicals. As an immune factor, it stimulates the immune system, and has anti-inflammatory and bacteriostatic properties. It is an anticancer agent that inhibits the binding of neoplastic growth factors, thus preventing the development of cancer and inhibiting the development of Alzheimer disease (25, 26).
Goat milk fat and its properies
The quality and nutritive value of animal products is subject to constant evaluation and review, if only due to the high proportion and unfavorable composi-tion of animal fats, mainly the high proporcomposi-tion of satu-rated acids and the insufficient proportion of unsatu-rated acids, especially essential unsatuunsatu-rated fatty acids (EUFA). According to FAO recommendations, with the desired 30% proportion of fat energy in total energy of the human diet, one-third of this energy should be from saturated fatty acids (SFA), over one-third from monounsaturated fatty acids (MUFA), and less than one-third from polyunsaturated fatty acids (PUFA) (12). Excessive consumption of SFA causes a number of metabolic disorders, resulting in many diseases such as obesity, atherosclerosis, cholelithiasis, diabetes, and cancer, especially cancer of the colon and prostate cancer. Of the long-chain fatty acids in milk, PUFA are the most valuable for consumers because of their anticancer, antiatherosclerotic, hypotensive, antibac-terial and immune-boosting properties. Of great signi-ficance are families of PUFA acids: linoleic C18:2, n-6 and á-linolenic C18:3, n-3. None of these acids is synthesized in the human body, although they can be converted within families. Their metabolites are
pre-cursors of eicosanoids: prostaglandins, thromboxanes and leukotrienes, the hormones that serve many regu-latory functions in the body (16, 27).
Eicosanoids, synthesized from n-6 acids, are cha-racterized by high biological activity even in small amounts. For this reason, excessive consumption of n-6 acids is unfavorable as it may induce thrombotic changes. Protective action is shown by eicosanoids synthesized from n-3 acids, which is why the proper n-6 to n-3 ratio in the diet is so important (preferably 2 : 1). According to Polish standards, this ratio should be 4-6 : 1 (37).
The quality of fat is largely determined by the con-tent of individual fatty acids. Data in table 4 show that the profile of fatty acids is more beneficial in goat milk compared to sheep and bovine milk because of the UFA/SFA ratio of 0.56 vs. 0.37.
In recent years, researchers have given much atten-tion to conjugated dienes of linoleic acid C18:2 (CLA), in which, unlike in linoleic acid, both cis and trans double bonds are isolated by a single bond. Conjuga-ted linoleic acid, also known as rumenic acid, is for-med as a result of enzymatic reactions by Butyrivibrio fibrisolvens symbiotic bacteria found in the rumen of ruminants. Monogastric animals are less capable of producing CLA (11). 100 g of goat milk contains about 25 mg of CLA (20, 21).
Research on the role of conjugated dienes of linoleic acid showed that they inhibit the incidence and growth of cancer in animals and humans, among others by preventing the proliferation of malignant melanoma, and colon, lung and breast cancer. CLA was also shown to prevent osteoporosis and atherosclerosis, to increase immunity and to reduce fatty tissue. The conjugated diene of linoleic acid is undoubtedly a functional com-ponent of goat milk fat (2, 4, 17, 20, 21, 25, 35).
Another important component of the human diet in addition to conjugated linoleic acid is the cholesterol content of food products. Current recommendations suggest that daily consumption of cholesterol should not exceed 300 mg. Research (8, 18, 28, 36) has shown that 100 ml of goat milk contains from 12 to 17 mg of s e i c e p S SFA UFA MUFA PUFA UFA/SFA MUFA/PUFA s ' p e e h S 65.60 34.40 27.10 7.30 0.52 3.71 s ' w o C 72.80 27.20 22.70 5.20 0.37 4.36 s 't a o G 64.50 35.50 29.93 5.57 0.55 5.34 Tab. 4. Fatty acid profile (%) of milk fat ruminants (21)
Tab. 5. Cholesterol content of ruminant milk (mg/100 ml) s e i c e p S Cholesterol Source t a o G 10.7114--1116.06 3 1 . 4 1 7 0 0 2 , a k c a n r e B 0 0 0 2 ,i k s w e l k e R 1 0 0 2 ,. l a t e i k s w o tj ó W w o C 13.10 Pe³czyñska,1996 p e e h S 26.11-29.0 Wótjowskietal,.2001
cholesterol, which is almost half of that in sheep milk (tab. 5).
Although it has various positive roles in the body by contributing to the formation of hormones, bile acids, vitamin D3 and other compounds, cholesterol may be hazardous to the health and even life of humans as it often causes the atherosclerosis of vital arteries. Cholesterol found in dairy products is fairly resistant to autooxidation processes, which is due, among others, to the low content of Fe and Cu that act as pro-oxidants and to the saturated fatty acid environment. Total cholesterol concentration in the blood largely depends on the content of some satu-rated fatty acids, as evidenced by positive correlations between these milk components (28).
Minerals and vitamins
Functional components of goat milk also include minerals (tab. 6). In terms of mineral composition, goat milk surpasses cow milk in the content of calcium, phosphorus and potassium. The mineral content of goat milk is 3 to 4 times that of womans milk, which is a considerable burden on kidneys in infants. For this reason, it is recommended that goat milk be given to infants (preferably over 6 months of age) after dilution and supplementation of missing components (14, 19).
Milk is the first food and contains a rich array of vitamins necessary for normal growth of young orga-nisms. The most important are fat-soluble vitamins A (axerophtol), D (calcipherol), E (tocopherol) and K (menaquinones, phylloquinone) and water-soluble vitamins B1 (thiamine), B2 (riboflavin), B6 (pyrido-xine), PP (nicotinic acid, niacin), B12 (cobalamine), pantothenic acid, C (ascorbic acid) and H (biotin). After precipitation of milk proteins, water-soluble vitamins mostly pass into whey. Comparative studies of goat and cow milk suggest that both types of milk contain similar amounts of vitamins B6 and pantothenic acid. Goat milk is higher in niacin, vitamins A and C (tab. 6). Orotic acid (vitamin B13) takes part in conversion of folic acid and vitamin B12, reduces cholesterol con-centration in the blood, has detoxifying and antiarthri-tic action (reduces the concentration of uric acid in the blood), prevents over-fatness of tissues, increases body weight gains through muscle mass gain and growth of connective tissue, as well as protecting parenchyma-tous organs (liver, kidneys) and the heart from dege-neration, cirrhosis and steatosis. Orotic acids are found in all organs, mainly the liver, spleen and heart, with considerable amounts found in milk.
Vitamin B13 acid content in the milk of sheep is highest and amounts to 350-450 mg/l, 100 mg/l of bovine milk, 63 mg/l of goat milk and 7 mg/l human milk (16, 20).
The information presented on the health pro-perties of goat milk suggest paying more attention to this product. Increased consumption of milk and its
products can be one of the most effective, while the cheapest, components in the prevention of lifestyle diseases: hypertension, atherosclerosis, obesity, diabe-tes and cancer.
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Adres autora: dr hab. in¿. Henryka Bernacka, prof. UTP, ul. Mazowiec-ka 28, 85-084 Bydgoszcz; e-mail: bernacMazowiec-ka@utp.edu.pl
