International Dairy Journal 20 (2010) 609e629
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International Dairy Journal
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Review Equine milk proteins: Chemistry, structure and nutritional significance
Therese Uniacke-Lowe a,*, Thom Huppertz b, Patrick F. Fox a a Department of Food & Nutritional Sciences, College of Science, Engineering and Food Science, University College Cork, Ireland b NIZO food research, P.O. Box 20, 6710 BA Ede, The Netherlands article info abstract
Article history: Equine milk has important nutritional and therapeutic properties that can benefit the diet of the elderly, Received 24 October 2009 convalescent or newborn. The protein content of equine milk is lower than that of bovine milk but Received in revised form similar to that of human milk. In this review qualitative and quantitative differences between the caseins 13 February 2010 and whey proteins of equine, bovine and human milk are discussed. Important biological and functional Accepted 17 February 2010 properties of specific proteins are reviewed and their significance in human nutrition considered. As well as characterizing equine milk proteins in the context of human nutrition and allergology, the potential industrial exploitation of equine milk is explored. Cross-reactivity of proteins from different species is discussed in relation to the treatment of cows’ milk protein allergy. While there is some scientific basis for the special nutritional and health-beneficial properties of equine milk based on its protein compo- sition and similarity to human milk, further research is required to fully exploit its potential in human nutrition. Ó 2010 Elsevier Ltd. All rights reserved.
Contents
1. Introduction ...... 610 2. Gross composition of equine milk ...... 610 3. Factors that affect the composition of equine milk ...... 611 4. Equine milk proteins ...... 611 4.1. Wheyproteins ...... 612 4.1.1. b-Lactoglobulin ...... 612 4.1.2. a-Lactalbumin ...... 612 4.1.3. Lactoferrin ...... 613 4.1.4. Lysozyme ...... 616 4.1.5. Immunoglobulins ...... 616 4.2. Denaturation of whey proteins ...... 617 4.3. Caseins ...... 617
4.3.1. as1-Casein ...... 617 4.3.2. as2-Casein ...... 618 4.3.3. b-Casein...... 618 4.3.4. k-Casein...... 619 4.3.5. Glycosylation of k-casein ...... 619 4.3.6. Hydrolysis of k-casein...... 619 5. Equine casein micelles ...... 620 5.1. Colloidal stability of casein micelles ...... 620 5.2. Enzymatic coagulation of equine milk ...... 621 5.3. Acid-induced flocculation of equine milk ...... 621 5.4. Heat-induced coagulation of equine milk ...... 621
* Corresponding author. Tel.: þ353 21 4902885; fax: þ353 21 4270001. E-mail address: [email protected] (T. Uniacke-Lowe).
0958-6946/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.idairyj.2010.02.007 610 T. Uniacke-Lowe et al. / International Dairy Journal 20 (2010) 609e629
6. Non-protein nitrogen of equine milk ...... 621 6.1. Bioactive peptides ...... 621 6.2. Free amino acids in equine milk ...... 622 7. Digestibility of equine protein ...... 622 8. Equine milk in human nutrition ...... 622 8.1. Cow milk protein allergy ...... 622 8.2. Cross reactivity of proteins ...... 623 9. Products from equine milk ...... 623 9.1. Koumiss ...... 623 9.2. Processing of equine milk products ...... 624 10. Conclusions ...... 624 References ...... 625
1. Introduction small udder size that limits exposure of the teats to infection (Doreau & Martin-Rosset, 2002) and despite its high level of Although horses are of minor importance for milk production in unsaturated fatty acids, equine milk has better keeping quality than comparison with cows, buffalo, sheep and goats, they have been human or bovine milk (Kalliala et al., 1951). For details on the traditionally important dairy animals in Mongolia and in the production of equine milk and the factors that affect it, the reader is southern states of the former Soviet Union, e.g., Kazakhstan, referred to the reviews by Doreau (1994), Doreau and Boulot Kyrgyzstan and Tajikistan. Because equine milk resembles human (1989), Doreau, Boulet, Bartlet, and Patureau-Mirand (1990), milk in many respects and is claimed to have special therapeutic Doreau and Martin-Rosset (2002) and Park, Zhang, Zhang, and properties (Freudenberg, 1948a, 1948b; Kalliala, Seleste, & Hallman, Zhang (2006a). 1951; Stoyanova, Abramova, & Ladoto, 1988; Lozovich, 1995), it is becoming increasingly important in Europe, especially in France, 2. Gross composition of equine milk Italy, Hungary and the Netherlands. Koumiss (fermented equine milk) is used in Russia and Mongolia for the management of Young mammals are born at very different stages of maturity digestive and cardiovascular diseases (Levy, 1998; Lozovich, 1995); and their maternal milk differs greatly in composition (Table 1), in Italy, equine milk is recommended as a substitute for bovine milk although milk from species in the same taxonomic order, e.g., the for allergic children (Curadi, Giampietro, Lucenti, & Orlandi, 2001). equids, tend to be fairly similar (Table 2)(Jenness, 1974a). The Overall, equine milk is considered to be highly digestible, rich in composition of equine milk differs considerably from that of the essential nutrients and possesses an optimum whey protein/casein milk of the principal dairying species, i.e., the cow, buffalo, goat and ratio, making it suitable in paediatric dietetics. Estimates suggest sheep (Table 1). In comparison with bovine milk, equine milk that more than 30 million people worldwide drink equine milk contains less fat, protein, inorganic salts but more lactose, with regularly, with that figure increasing significantly annually (Doreau a concentration close to that in human milk. A mare produces & Martin-Rosset, 2002). However, in comparison with bovine milk, 2e3.5 kg milk per 100 kg live-weight per day to sustain the rapid equine milk is very expensive to produce. One of the main growth of the foal (Doreau, 1994; Oftedal, Hintz, & Schryver, 1983). constraints of the horse as a dairy animal is the high frequency of A healthy foal will consume 10e25% of its body weight of milk per milkings required; generally about 5 times per day or every 2 h, day (Gibbs, Potter, Blake, & McMullan, 1982; Oftedal et al., 1983; with the foal feeding through the night. The capacity of the mare’s Zicker & Lönnerdal, 1994), which for an average 45 kg foal is udder is low, about 2 L, and the foal must be in close proximity 9e13 L of milk daily (Paradis, 2003). The composition and during milking (Solaroli, Pagliarini, & Peri, 1993). Unlike dairy cows, constituents of equine milk have been studied thoroughly; reviews mastitis is not a major factor in equine milk production due to the include Doreau and Boulot (1989), Linton (1931), Malacarne,
Table 1 Gross composition of the milk of selected species.
Species Total Protein Casein/whey Fat Lactose Ash Gross References solids ratio energy Man (Homo sapiens)a 124.0 9.0 0.4:1 38.0 70.0 2.0 2763c Hambræus (1982, 1984); Picciano (2001) Cow (Bos taurus)b 127.0 34.0 4.7:1 37.0 48.0 7.0 2763d Jenness (1974b) Horse (Equus caballus)a 102.0 21.4 1.1:1 12.1 63.7 4.2 1883c Malacarne et al. (2002); Schryver, Oftedal, Williams, Soderholm, and Hintz (1986) Donkey (Equus africanus asinus)a 88.4 17.2 1.3:1 3.8 68.8 3.9 1582 Salimei et al. (2004) Buffalo (Bubalus bubalis)a 172.0 46.5 4.6:1 81.4 48.5 8.0 4644c Jenness and Sloan (1970); Tufarelli, Dario, and Laudadio (2008) Sheep (Ovis aries)b 181.0 55.9 3.1:1 68.2 48.8 10.0 4309d Raynal-Ljutovac, Lagriffoul, Paccard, Guillet, and Chilliard (2008) Goat (Capra hircus)a 122.0 35.0 3.5:1 38.0 41.0 8.0 2719c Park, Zhang, Zhang, and Zhang (2006b) Camel (Camelus dromedarius)b 124.7 33.5 1.68:1 38.2 44.6 7.9 2745d Konuspayeva, Faye, and Loiseau (2009), Vaisman, Reuven, Uzi, Georgi, & Boehm, (2006) Llama (Llama glama)b 131.0 34.0 3.1:1 27.0 65.0 5.0 2673d Rosenberg (2006) Yak (Bos grunniens)a 160.0 42.3 4.5:1 56.0 52.9 9.1 3702c Silk, Guo, Haenlein, and Park (2006); Sheng, Li, Alam, Fang, and Guo (2008)