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HYPO-ALLERGENIC & THERAPEUTIC
SIGNIFICANCE OF GOAT MILK
By: "Dr. Young W. Park"
Goat milk has been recommended as substitute for patients allergic to cow milk. Between 40 to 100% of patients allergic to cow milk proteins tolerate goat milk. Although some caprine milk proteins have immunological crossreactivity with cow milk proteins, infants suffering from gastrointestinal allergy and chronic enteropathy against cow milk were reportedly cured by goat milk therapy. The higher protein, nonprotein N and phosphate in caprine milk give it greater buffering capacity compared to cow milk. Some physico-chemical properties of caprine milk such as smaller fat globules, higher percent of short and medium chain fatty acids, and softer curd formation of its proteins are advantageous for higher digestibility and healthier lipid metabolism relative to cow milk. Goat milk also has a greater iron bioavailability in anemic rats than cow milk. Further studies of the hypo-allergenic and therapeutic significance of goat milk to humans are very much needed.
Goat milk differs from cow or human milk in unique characteristics, such as high digestibility, distinct alkalinity, high buffering capacity as well as certain therapeutic values in medicine and human nutrition (Gamble et al., 1939; Rosenblum and Rosenblum, 1952; Walker, 1965; Devendra and Burns, 1970; Haenlein and Caccese, 1984; Park and Chukwu, 1988; Park, 1991).
Goat milk has been recommended as substitute for those who suffer from allergies to cow milk or other food sources (Rosenblum and Rosenblum, 1952; Walker, 1965; Van der Horst, 1976; Taitz and Armitage, 1984). Cow milk allergy (CMA) is a frequent disease in infants, but its etiologic mechanisms are not clear. Increased gastrointestinal absorption of antigens followed by adverse local immune reactions may constitute a major etiological factor in development of food allergies like CMA (Walker, 1987). The prolonged inadvertent exposure of cow milk to infants having CMA was associated with an inflammatory response in the lamina propia and a constant increase in macromolecular permeability and electrogenic activity of the epithelial layer, even in the absence of milk antigen (Robertson et al., 1982; Heyman et al., 1988). These clinical disease symptoms are transient, since all the disease parameters returned to normal after several months on a cow milk-free diet (Heyman et al., 1990).
Potentials of goat milk as the substitute for cow milk or the basis of cow milk-free diet are of great importance to infants and other patients with CMA, goat milk consumers and producers as well as goat milk industry. The purpose of this paper is to review comprehensively research concerning hypo-allergenicity and therapeutic values of caprine milk in humans.
Pathogenesis of Food Allergy
Milk allergy is not confined to infancy, but is also seen as persisting allergy in children and adults (Deamer et al, 1979; Heyman and Desjeux, 1992). Most children under 3 years of age around the world have circulating milk antibodies (Eastam and Walker, 1977). However, approximately 7% of these children in the US (probably in all Western countries) have symptoms of milk protein allergy (Gerrad et al., 1973; Haenlein, 1992; Podleski, 1992). The type of immune response after intrusion of foreign proteins is extremely variable, depending on the animal species, the age of the host, the quality and quantity of antigens absorbed, the location of the absorption, the pathophysiological state, and genetic background, etc. (Heyman and Desjeux, 1992).
Prolonged breast-feeding up to 6 months and a delay in the introduction of cow milk and solid foods lessens the risk of the appearance of allergic manifestations in babies from atopic families (Saarinen et al., 1979; Foucard, 1985). Infants with minimal exposure to cow milk showed vastly increased total and milk specific IgE antibodies compared with the milk-fed infants (Firer et al., 1981). Bovine milk allergy involves IgE responses, where ß-lactoglobulin is a milk protein highly resistant to intestinal luminal hydrolysis and mostly responsible for cow milk allergy (Taylor, 1986; Robertson et al., 1982; Heyman and Desjeux, 1992).
Many foods are capable of causing allergic symptoms as shown in Table 1 (Walker, 1965; Rapp, 1981). However, cow milk is the most frequent cause of food allergy, especially in children (Rosenblum and Rosenblum, 1952; Walker, 1965; Van der Horst, 1976; Firer et al., 1981; Robertson et al., 1982; Podleski, 1992; Heyman and Desjeux, 1992). Apparently, more than one mechanism exists for milk allergy and more than one is involved in particular patients even when there is a single clinical manifestation (Podleski, 1992), which has made it difficult to understand (Eastham and Walker, 1979; Deamer et al., 1979; Heyman and Desjeux, 1992; Podleski, 1992).
In understanding pathogenesis of food allergy, two integral aspects of disease mechanisms have been proposed and many studies on the premises have been reported. These are: (a) mechanism of antigen absorption by the gut, and (b) mechanism of immune response by the host cell or animal.
(a) Mechanism of antigen absorption by the gut
Under normal physiological conditions, some amounts of macromolecules such as food antigens constantly absorbed by the intestinal epithelium (Heyman and Desjeux, 1992). It is difficult to quantify the exact amount of protein that acrosses the intestinal epithelium due to a number of interactions involved before and after epithelial transport.
Using in vitro methods in which intestinal fragments are tested in Ussing chambers, protein transport from the intestinal epithelium has been measured quantitatively (Marcon-Genty et al., 1989; Isolauri et al., 1990). Two functional pathways of protein antigen absorption by transcytosis have been proposed as shown in Figure 1. (Heyman et al., 1982; Isorauri et al., 1990; Heyman and Desjeux, 1992). The main pathway is degradative pathway involved in lysosomal processing of the protein. This processing does not imply total hydrolysis of the protein but generates new antigenic determinants with MW of 2,000-4,000 which may still interact with the underlying immune cells (Heyman et al., 1982). More than 90% of the protein internalized passes in this way, and the magnitude of the absorption is about 2-4 µg/h × cm2 (Marcon-Genty et al., 1989). The second pathway of the protein antigen absorption is direct transcytosis which is a minor one. This pathway involves the transport of the intact protein which cmprises of <10% of the total transport (Isolauri et al., 1990; Heyman and Desjeux, 1992).
(b) Mechanism of immune response by host cell (animal)
The first type reaction is immediate hypersensitivity. IgE-specific antibodies become bound to mast cells or basophils, which react on reexposure to the allergen, causing mediators such as histamine to be released (Worthington et al., 1974; McClenathan and Walker, 1982; Podleski, 1992). Mediators are stored in the body cells and released when triggered by a local stimulus (Hyeman and Desjeux, 1992; Podleski, 1992). The mediators act on local tissues, causing vasodilation, smooth muscle contraction, and secretion of mucus. Release of histamine also brings on a congestion of capillaries and flooding of intracellular spaces by lymphatic glands (McClenathan and Walker, 1982; Haenlein and Caccese, 1984). Stimulation of local nerve endings also occurs. On pathologic examination, affected areas show submucosal edema, dilated blood vessels, and eosinophilic infiltration. Mast cell degranulation and an increase in number of IgE-staining plasma cells may be seen in the intestinal interstitium (May and Bock, 1978; Firer et al., 1981). Persons with an allergic reaction are usually more sensitive to the release of histamine and tend to produce greater numbers of antibodies to certain proteins (Haenlein and Caccese (1984). Mostly milk allergy is not reagin (IgE) mediated (Deamer et al., 1979).
The second type of immunologic mechanism is considered to have several pathways: Non-reaginic antibodies react with antigen-forming complexes that in turn activate a complement system, causing inflammation and/or cytopathic effects (McClenathan and Walker, 1982). Another mechanism which is probably not immunologically mediated in food allergy may be direct intestinal mucosal toxicity of the protein or its breakdown fragments, as suggested in gluten enteropathy. The hydrolysis of the absorbed proteins allows the formation of peptides that might be implicated in lyphocyte activation (Bland, 1987; Mayrhofer and Spargo, 1987; Heyman and Desjeux, 1992). In a given patient, it is likely that several mechanisms operate simultaneously with one predominating and the others contributing to the reaction (Heyman and Desjeux, 1992; Podleski, 1992).
Clinical Manifestations of Cow Milk Allergy
Bovine milk eosinophilic induced colitis among children is well established (Wilson et al., 1990). Clinical symptomatology to bovine milk is related to bronchospasm, rhinitis, diarrhea, erythema, and eczema (Husby et al., 1990). The following symptoms of documented bovine milk protein allergy were found: rhinitis (43%), diarrhea (43%), abdominal pain (41%), anaphylaxis (10%), and urticaria (7%) (McClenathan and Walker, 1982). In a study of 45 children having various gastrointestinal, dermatologic and respiratory symptoms suspected to be caused by cow milk allergy, Bahna (1991) gave oral challenge with whole bovine milk and skin testing supplemented with intradermal whole bovine milk, casein and a-lactalbumin. Tests were positive in 23 subjects: Concordance (both tests positive and negative) between the results of whole milk challenge and skin testing with bovine milk was 45%, with casein 51% and a-lactalbumin 31%. Pahud et al. (1985) observed that guinea pigs which had been orally sensitized to demineralized whey were sensitized to several whey proteins (ß-lactoglobulin, a-lactalbumin, and immunoglobulin). They reported highest titers in cutaneous anaphylaxis with ß-lactoglobulin, lower titers with other whey proteins. Demineralized whey protein lost its sensitizing capacity when it was hydrolyzed with trypsin. Among children allergic to cow milk, the group who were breast fed and had minimal exposure to cow milk showed decreased titers of IgG, IgA, and IgM milk antibodies than the group fed sustantial volumes of cow milk (Firer et al., 1981).
Pathophysiological symptoms of milk allergy may be clinically menifested in two major sites: small intestine and colon. Typical symptoms of patients having pathological reaction in small intestine are irritable, fail to gain weight, and have bulky, foul-smelling diarrhea stools (Worthington et al., 1974; McClenathan and Walker, 1982). A 72-hr fecal fat measurement for these patients often showed fat malabsorption and abnormal fat values in the stool. Observations on small-bowel biopsy may be indistinguishable from those in celiac disease. Histologic changes range from a moderate inflammatory cell infiltrate of the lamina propria to a totally flattened villous lesion with chronic inflammatory changes (Fontaine and Navarro, 1975). Bacterial infections, viral enteritis and malnutrition are often associated histological intestinal lesions, which interact with pathological reactions of milk allergy in intestinal villi through increased permeability of antigen molecules (Isolauri et al., 1990; Heyman and Desjeux, 1992). Besides cow milk, foods that have been found to cause blunting of intestinal villi are soy, gluten and egg (Eastham et al., 1978).
The typical clinical symptom of pathological reaction in colon is diarrhea with occult blood and mucus in the stool. Sigmoidoscopic findings showed erythema, edema, small ulcers, and spontaneous mucosal friability in colon (McClenathan and Walker, 1982). Histologic characteristics on rectal biopsy revealed that there was infiltration of the lamina propria by lymphocytes, plasma cells, eosinophils, and neutrophils, with destruction of the surface epithelium, crypt abscesses, and distortion of rectal glands (Gryboeld et al., 1966). Food allergy can also be observed with delayed symptoms due to the activation of T lymphocytes. These activated lymphocytes release lymphokines, including various interleukins, tumor necrosis factor and ?-interferon that might affect intestinal epithelial permeability (Heyman et al., 1990). In manifestation of milk allergy, one should be cautious of patients' symptomatology with reference to that of lactose intolerance. Many humans in certain parts of the world gradually lose some or all of the intestinal enzyme lactase after infancy to digest lactose. Deficiency of lactase causes clinical symptoms, which can persist in some racial groups and are often confused with common symptoms of bovine milk allergy.
Hypo-Allergenicity of Goat Milk
Brenneman (1978) reported that approximately 40% of allergic patients, sensitive to cow milk proteins, are able to tolerate goat milk proteins. These patients may be sensitive to cow lactalbumin which is species specific. Other milk proteins, such as ß-lactoglobulin which is mostly responsible for cow milk allergy (Zeman, 1982; Heyman and Desjeux, 1992). Walker (1965) reported that only one in 100 infants who were allergic to cow milk, did not thrive well on goat milk. Of 1682 patients with allergic migraine, 1460 were due to food, 98 due to inhalants, 98 due to endogenous (bacterial), and 25 due to drugs (including tobacco). Among the 1460 patients with food allergy, 92% were due to cow milk or dairy products; 35% wheat; 25% fish; 18% egg; 10% tomato; 9% chocolate. Some patients were allergic to more than one food.
Soy formula is the most frequent substitutes for cow milk or cow milk formula for infants suspected of cow milk allergy, but approximately 20-50% of these infants will still have similar intolerance symptoms to soy formula (Halpla et al., 1977; Chandan et al., 1992). Evaporated goat milk or goat milk powder has been recommended for infant formula (McLaughlan et al., 1981; Juntunen and Ali-Yrkko, 1983; Taitz and Armitage, 1984; Coveney and Darnton-Hill, 1985). Heat applied to manufacturing processes reduces allergic reactions (Perlman, 1977). Heat denaturation alters basic protein structure by decreasing its allergenicity (Macy et al., 1953), and high heat treatment removes sensitizing capacity of milk (McLaughlan et al., 1981). Since as1-casein content of goat milk is relatively low, it is logical that children with high sensitivity to as1-casein of cow milk should tolerate goat milk quite well (Juárez and Ramos, 1986; Chandan et al., 1992).
Lactalbumin from goat milk shows a different skin reaction in comparison to bovine milk. Perlman (1977) reported the variation of skin test reaction to allergenic fractions of bovine milk and goat milk (Table 2). The data indicates that some proteins of bovine milk gave higher incidences of positive skin test reactions than goat milk. Inconsistency in cross-allergenicity among milks of different species may be qualitative and quantitative (Podleski, 1992). A few reports using gel electrophoretic precipitation analysis also suggested that there was a certain immunological crossreactivity between cow and goat milk proteins (Saperstein, 1960; Parkash and Jenness, 1968; Saperstein, 1974; McClenathan and Walker, 1982). However, little clinical research has demonstrated that goat milk is not suitable for patients allergic to cow milk due to the immunological crossreactivity between the two milk proteins.
Many anecdotal evidences of goat milk values as a hypo-allergenic substitute for children allergic to bovine milk milk have been reported (Podleski, 1992). There are limited data on basic immunology and biological mechanisms to support clinical observations why goat milk can substitute for cow milk in allergic patients.
Therapeutic and Special Nutritional Merits of Goat Milk
Average size of goat milk fat globules is smaller than that of cow and other species milks. Comparative average diameters of fat globule for goat, cow, buffalo and sheep milk were reported as 3.49, 4.55, 5.92, and 3.30 µm, respectively (Fahmi et al., 1956; Juarez and Ramos, 1986). The smaller fat globule size of goat milk would have better digestibility compared to cow milk counterparts (Haenlein and Caccese, 1984; Stark, 1988; Chandan et al., 1992). It has been also claimed that goat milk proteins are digested more readily and their amino acids absorbed more efficiently than those of cow milk. Goat milk is considered to form a softer, more friable curd when acidified, which may be related to lower content of as1-casein in the milk (Jenness, 1980; Haenlein and Caccese, 1984; Chandan et al., 1992). It may be logical that smaller, more friable curds would be attacked more rapidly by stomach proteases (Jenness, 1980).
Goat milk also had a greater iron bioavailability in anemic rats than cow milk (Park et al., 1986). Anemic rats fed on goat milk grew significantly better, had higher liver weights and hemoglobin regeneration efficiency than those on cow milk. Mack (1953) also observed that children on goat milk group surpassed those on cow milk in weight gain, statue, skeletal mineralization, bone density, blood plasma vitamin A, calcium, thiamine, riboflavin, niacin, and hemoglobin concentrations. However, goat milk has been blamed for development of the "goat milk anemia" due to deficiencies of folic acid and vitamin B12 in the milk (György, 1934; Collins, 1962; Nicol and Davis, 1967; Davidson and Townley, 1977; Park et al., 1986).
Goat milk has better buffering capacity, which is good for the treatment of ulcers (Devendra and Burns, 1970; Haenlein and Caccese, 1984; Park, 1991; Park, 1992). Proteins, primarily casein and phosphate systems in milk, influence its buffering capacity (BC) (Watson, 1931). Nubian goat milk showed a higher BC compared with Alpine, Holstein and Jersey cow milks (Park, 1991). Major buffering entities of milks were influenced by species and breeds within species (Table 3). Nubian goat milk had highest levels of total N, protein, non-protein N (NPN) and phosphate (P2O5) among the 4 breeds of goat and cow milks. Regardless of breed, goat milk contained significantly higher non-protein N than cow milk. The higher levels of nitrogen moieties and phosphate in goat milk were positively correlated with higher BC (Park, 1991). Soy-based infant formulae contained less total N and NPN compared with natural goat and cow milks, and BC of the formulae were also lower than those of natural milks (Fig. 2). This suggests that higher BC in Nubian goat milk compared to cow milk can be of importance in human nutrition.
Table 1. - Major causes of food allergy
Table 2. Variations in skin test reactions to fractions of cow milk and goat milk.
1Beta-lactalbumin heated to 100oC still gave ++ reaction but after heating to 120oC for 20 min all skin test reactions disappeared.
Table 3. Concentration of total N, NPN, and phosphate in natural goat and cow milk and soy-based infant formulas1.
About the author: additionally...for more information about dairy goats, write to us at:|
Dr. Young Park
Associate Professor of Animal & Food Sciences
Agricultural Research Station
Fort Valley State University
1005 State University Drive
Fort Valley, GA 31030-3298
College of Agriculture, Home Economics, & Allied Programs
Fort Valley State University
Fort Valley, Georgia 31030
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