rganic v s. C on ventional F
ood and Eff
ec
ts
on
Health
(Ng-Kwai-Hang et al., 1984). Among them, a nutrition method is essential, since it affects the content of fat, especially its composition. Climatic conditions are of little impact unless they are extreme and may cause animal stress. In addition, milking practice may involve changes in many ways in the composition of milk. The shorter the milking interval, the lower the cow’s productivity, and the milk contains more fat (Weiss et al., 2002). Therefore, milk from the evening milking is fattier than from the morning one (Quist et al., 2008).
Organic milk has an advantage over conventional milk in terms of nutri- ent content during the season of pasture grazing, and throughout the year it has a greater security for consumers (Butler et al., 2008). One of the reasons is the ban of the use of synthetic pesticides in organic farming. In conventional milk production the use of over a thousand different pesticides is permitted for the plant protection. Research conducted by the USDA (United States Department of Agriculture) has detected the presence of pyrethroid pesticides in 27% of con- ventional milk samples and among organic samples, only one sample has a low content of these substances (Benbrook, 2005). In conventional farms the antibi- otics are often routinely and prophylactically given to animals. The question of the impact of antibiotic use in conventional cows’ husbandry on the increase in the resistance of the human body to these measures is being discussed. In certi- fied organic farms such practices are prohibited. The use of synthetic hormones and genetically modified ingredients in feed is also not allowed in the organic system. The analysis of heavy metals in both types of milk showed no differ- ences between them, detecting low contamination of all samples (Gabryszuk et al., 2008).
The chemical composition of milk is an indicator of quality, not only for its consumers, but also for processors. High protein content is important in the production of cheese, while high fat content is essential in butter manufacturing. Beta-carotene increases the intensity of butter colour, so it is also considered in the assessment of technological quality. For many dairy products, an important role is played by the antioxidant level, which avoids undesirable losses caused by excessive oxidation of fats (Abrahamsen et al., 2008). The degree of saturation of fatty acids, in turn, affects the hardness, texture and flavour of dairy prod- ucts, especially cheese and butter (Chen et al., 2004). The presence of long chain saturated fatty acids increases the hardness of butter, while the milk with a high content of unsaturated fatty acids gives softer products (e.g., better spreadability of butter) (Butler et al., 2008).
Milk obtained from organic farms represents about 2% of total milk pro- duction in the EU (Agra Europe, 2007). A strong demand for such milk is also observed in the United States (Hale, 2006).
Dry matter and proteins
The dry matter of milk mainly consists of proteins and peptides. The largest share (80%) among these compounds belongs to casein, which is responsible for clot formation, making it possible to digest milk in the stomach and to transfer phos- phorus and calcium (Haug et al., 2007). They also regulate blood pressure, have anticoagulation, hypnotic, immunomodulatory and anti-bacterial effects (Kitts, 2005). Whey proteins are considered to be the second largest fraction of pro-
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4. NUTRITIONAL
VAL
UE OF ORGANIC v
s. C
ONVENTIONAL ANIMAL PRODUC
TS
teins, important in a human diet due to the immunostimulatory (Korhonen et al., 2000), anticancer (Parodi, 2007), antioxidant (Pihlanto, 2006) and bacterio- static activities (Kitts, 2005).
So far, several studies have compared the quality of milk from different pro- duction systems (table 8, pp. 56–57). Zadoks (1989) and Lund (1991) found in their studies that organic milk contains more dry matter, while Guinot-Thomas et al. (1991) reported this concentration comparable in both systems. For protein content, results of the studies have been also variable – the majority of the stud- ies have shown the decreased content of protein in organic milk compared with conventional (Guinot-Thomas et al., 1991; Luukkonen et al., 2005; Roesch et al., 2005; Słoniewski et al., 2005). However, Lund (1991) showed higher content of proteins in organic milk and Zadoks (1989) found no differences between the systems.
Fatty acids
Dietary milk fats, on account of their higher content of saturated fatty acids (SFA), have long been associated with a variety of human diseases (Parodi, 1977), such as atherosclerosis and increased levels of blood cholesterol, which contributes to cardiovascular diseases (Pfeuffer and Schrezenmeir, 2000). However, recent studies have focussed on the healthy components of milk fats (Parodi, 1977). In terms of fat content, cow’s milk is very variable. The fraction is made up of ap- proximately 95% of triacylglycerols, composed of fatty acids, whose chain length and saturation degree condition the nutritional value of milk fat. Among the unsaturated fatty acids, omega-3 polyunsaturated fatty acids (PUFA) have ben- eficial effects on the human body. They positively impact the nervous system as well as reduce the risk of diabetes and cardiovascular diseases (Horrobin, 1993; Hu et al., 1999). The proportion between the amount of omega-3 and omega-6 fatty acids is also important. If the acid content of the latter group is too high, it causes an increase in the risk of inflammation, thrombosis and autoimmune symptoms.
Among the n-3 (omega-3) fatty acids, the most important is alpha-linolenic acid (LNA), whereas among the n-6 (omega-6) fatty acids linoleic acid (LA) oc- curs in the largest quantities. As for monounsaturated fatty acids (MUFA), there should be mentioned oleic acid, which is about one quarter of the total mass of fatty acids. It acts protectively towards the omega-3 and omega-6 fatty acids, preventing them from oxidation, as well as lowering cholesterol level and has anticancer effects (Ip, 1997; Kris-Etherton et al., 1999; Mensink et al., 2003).
An important part in the composition of cow’s milk is occupied by conju- gated linoleic acid (CLA). The cow’s milk is the main source of the compound isomers in the human diet (Haug et al., 2004). The most important of them (rep- resenting approximately 90% CLA) is cis-9 trans-11 isomer, because it prevents the development of tumours, heart diseases, and stimulates the immune system (Whigham et al., 2000). It is called rumenic acid, since the rumen is where it is synthesised from linoleic acid. Other CLA isomers (trans-7 cis-9, trans-10 cis-12 and trans-9 cis-11) counteract obesity (by reducing fat and increasing muscle mass) and help to treat diabetes (Taylor and Zahradka, 2004). The content of CLA in milk fat is affected by a number of factors. First of all, it is the feed animals
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