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Scientific Research of the Union of Scientists in Bulgaria - Plovdiv, series B. Natural Sciences and Humanities, Vol. XVII, ISSN 1311-9192, International Conference of Young Scientists, 11 - 13 June 2015, Plovdiv
SOMATIC CELLS AND THEIR INFLUENCE ON MILK QUALITY Meri Ilijoska Coauthor: Nikola Popovski, Igorce Cokuzovski Mentor: Prof. Dr. Stefce Presilski University „St. Kliment Ohridski", Faculty of Biotechnical Sciences e-mail: meri_ilijoska@hotmail.com
Abstract
The somatic cells are a natural ingredient of milk, and their number in cow's milk should not be greater than 400,000 / ml. The increase of their number comes as a consequence off an infection of the mammary gland. Depending on the cause and extent of the infection the number of somatic cells can be up to 5 million / ml. The reduction in milk production and the change of its chemical composition, physical properties and processing all these attributes of the milk are manifested when the milk has more than 400 000 ml somatic cells. The disadvantage of the milk coming from infected udders (for technological purpose) can't be improved by any procedure, the only prevention is possible if the infection and inflammation of the udder is diagnosed on time. That allows the quality of the sour milk to be kept and improved. Determining the number of somatic cells in cow's milk is recommended as a mandatory measure for assessing the suitability of milk Introduction
The somatic cells as a natural ingredient of the milk have no influence on the changes of the rest of its composition, physical properties and bacteriological suitability. The number of somatic cells in milk today is internationally recognized parameter for udder health (Muggli, 1993), and they are measured in order to determine control of the health condition of the milk gland, preventing mastitis and enhancing milk quality (Olnej 1983; Muggli 1993). Their growing number is the result of inflammation of the udder, and manifests itself by changing the chemical composition and secretion of milk, physical, bacteriological and technological properties of milk.
According to the legislation of 01/02/1995, at E.Z countries (European Community), raw cow milk must not contain more than 400,000 somatic cells / ml (Soorrazin i Skoti, 1995; Tshischkale).
1.1 Definition of somatic cells
Somatic cells represent a combination of epithelial cells (70%) of the secreted udder tissue and leucocytes (30%) from the bloodstream, which consist of polymorph nuclear neutrophils (3540%), lymphocytes (20-25%), macrophages (20%) and other cells. The number of somatic cells in healthy udder may be 200,000 in 1 ml of milk. Stage and order of lactation, time, milking, storage, race, diet, and stress of the animals, all act and influence the number of somatic cells in milk.
The impact of the above factors is minimal if the milk gland is infected. In the milk of healthy animals leukocyte count is balanced in all quarters, but if there is certain increase in one of them that leads to the conclusion that there is mastitis and in such quarters, with impaired secretion content of somatic cells can be from 5.000.000 / ml. In fact, during mastitis, udder immune defense becomes active and the polynucleotide leukocytes move from the blood to the mammary glands in large numbers, and with that the number of somatic cells in milk increases.
1.2 Mastitis
Mastitis is a complex disease of the mammary gland which is usually caused by bacterial infection of the udder parts or a trauma, and results in reduced synthesis of milk and changes
to the specific components of milk, as it jeopardizes the quality of the milk. The most common causes of mastitis are Staphilococcus aureus, Streptococcus agalactiae, Strpotococcus spp (uberis, pyogenes, dysgalactitae), and coliforms. They increase the number of somatic cells up to a million / ml. (Reneau, 1986). This infection leads to an increased number of somatic cells (white blood cells), which actually represent the defense system of animals. Their primary function is to eliminate the infection and to rebuild diseased parts of the udder. When bacteria grow they release metabolites and toxins that stimulate the defense mechanism of the animal. As response to the inflammation there is a migration of white blood cells from the peripheral circulation into the udder.
Mastitis can be clinical and sub-clinical.
Clinical mastitis two provides abnormal milk and causes swelling or edema of udder. Bacteria is present in the milk, and therefore the composition of milk is changed.
Sub-clinical mastitis is more problematic because it does not cause visible changes in milk or the udder, but milk production decreases, bacteria is present in milk and the milk composition is changed.
The losses in the dairy industry resulting from the occurrence of mastitis are closely related to changes occurring in the composition of milk, decreased levels of calcium, lactose and casein, on the one hand and on the other hand, increased levels of sodium chloride, and serum proteins.
1.3 Changing the chemical composition of milk
A significant change in the chemical composition of the milk comes when the number of somatic cells is greater than 250,000 / ml (Rogers, 1989), and a more pronounced change when the number is greater than 750,000 / ml (Steffer, 1994).
Table 1: Change of the chemical composition of milk associated with an increase in the number of somatic cells
Нормално млеко % Млеко со висок % на соматски клетки
Fat 8,9 8,8
Lactose 3,5 3,2
Total proteins 3,6 3,56
Total Casein 2,8 2,3
Surutkini proteins 0,8 1,3
Sodium (Natrium) 0,057 0,11
Chlorides 0,091 0,15
Calcium 0,12 0,04
Solids without fat 8,9 8,8
Fat, lipase and free fatty acidsThe increased number of somatic cells in milk negatively affects milk fat. The amount of free fatty acids increases, and by activating the lipases are causing the occurrence of uzhegnatost in dairy products. All this leads to reduced production of butter but also to a reduction in quality.
Proteins in milk
An increased number of somatic cells in milk will cause a reduction in the amount of protein. This occurs as a result of increased activity of proteolysis enzymes in milk. One of these enzymes is plasmin that decomposes casein in the milk storage. Plasmin is transferred from blood plasma into milk through damaged parts of tissue. No major change occurs in the percentage of protein,
but the percentage of casein is reduced, and on account of that the proportion of surutkini proteins increases.
Lactose and sodium chloride
The increase in the number of somatic cells leads to reduced levels of lactose and increased levels of sodium chloride. This is the main reason why milk with a large number of somatic cells is classified as salty milk.
Vitamins
From research of water soluble vitamins it was concluded that reducing the amount of thiamine by 10% riboflavin by 6-20%, vitamin C by 20-40%. At the same time from the fat soluble vitamins we have increase in the quantity of the alpha and beta carotene because the composition of the milk comes close to the one of the blood serum.
Enzymes
In mastitis milk we have increase of the quantity of plasmin, alkaline phosphatases, catalases, lipases, xanthine - oxidase, lactate dehydrogenize, esterases, and (Kitchen 1981; Harmon 1994). Plasmin decreases the amount of beta casein, which is responsible for the strength of grushot. (Politis i Ng-Kwai hang, 1998).
Mineral materials
Because of the increased passage of sodium and chloride from the blood to the milk, it receives salty taste, while the amount of potassium and calcium is reduced due to switching off the lumen of the alveoli, which are broken and casein synthesis (Kitchen, 1981).
1.4 Changes of physical properties of milk
The milk that has a increase of the somatic cells also has different physical properties - ti-tracionic acidity and pH values. The acidity in mastitis milk with weaker form ranges from 4.8 to 5.6 SH° and from 3.2 to 4.0 in severely diseased form. By determining the pH value in milk we can diagnose mastitis. In mastitis milk pH is increased and ranges from 6.8 to 6.9, and in difficult diseased cattle and more than 7,0 (Harmon 1994). The increase of the pH comes as a result of the increased permeability of the gland tissue for the blood ingredients (components). This change of the pH value has a negative effect of the coagulation property of the milk.
1.5 Changing the organoleptic properties of milk
In the organoleptic properties the most noticeable is the change in taste which becomes vzeg-nat (don't know the meaning of this word) because of increased presence of free fat acids or better said it is salty because of the increase of sodium and chlorine. The milk has more water, and we also see a reddish color and noticeable clods of casein.
1.6 Changes to the technological properties of milk in cheese production
We have the strongest manifestation of the negative changes during the production of cheese with milk that has increased number of somatic cells. Deficiencies are manifested through the adverse relative relation of the casein fractions, increased pH value, change of the coagulating properties, decrease of the reproduction and the quality of the final product.
1.6.1 Coagulation properties of milk
The increased number of somatic cells in milk reduces the clotting ability of the same. The surutkin proteins are absorbed on the casein micelles and they reduce the ability to make cheese and forming grush. This results with hydrolysis of the beta-caesin (Kroeker et al 1988), which is important for the strength of grushot (Politis i Ng-Kwai Hang 1988). Thus created grushot retains the surutka, it's hard to process, and with the surutka it looses quite a large amount of casein and fat.
1.6.2 Reproduction and quality of the cheese
Reduced amount of cheese produced from milk that contained more than 500,000 SK / ml is 0.89 kg / 10 kg of cheese compared to milk which contains less than 250,000 s.k / ml. The quality of thus produced cheese is worse thanks to the content of larger quantity of water in the lean tissue of the cheese; it has increased stickiness, reduced elasticity, firmness and texture of the curd dough
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and bad taste (Grandison i Ford 1986).
Conclusion
From all that was said so far we come to the conclusion that there is a direct link between the presence of somatic cells and the composition of milk. In particular there is a close relationship between the level of somatic cells, the pH value of the milk and the content of surutkini proteins and lactose in milk, and the content of certain mineral elements. Also, the clotting factors depend on the presence of somatic cells, so that the increased presence of somatic cells in milk causes substantial slowdown in the process of coagulation and causes serious difficulties in structuring of the milk when producing cheese as well as the long duration of the process of getting the cheese.
So we can say that for the sake of milk-Manufacturing industry, as well as efficient management of dairy farms, and in order to increase efficiency and maximize profits thereof, breeders of animals that milk producers should fully succeed in reducing and complete removal of somatic cells in milk.
References:
1.Barker,A.R.(1990)-Influence of clinical mastitis during early lactation on reproductive performance
2. Ali, A.E. (1980)-Influence of elevated somatic cells count on casein distribution
3. Rajcevic,M.,Potocnik,K.,Levstek,J.-Original scientific paper, Correlation between somatic cells count and milk composition
4. Politis, I., and K. F. Ng Kwai Hang. 1988a. Effects of somatic cell counts and milk composition
on cheese composition and cheese making efficiency. J. Dairy Sci. 71:1711-1719.
5. Politis, I., and K. F. Ng Kwai Hang. 1988b. Association between somatic cell counts of milk and cheese yielding capacity. J. Dairy Sci. 71:1720-1727.
6. Ford G.D & Grandison, A.S., 1986. J. Dairy., Res.52,129
7. Olney G.R., Skott, G.W & Michell R.K . 1983 Effect of milking machine factors on the somatic cell count of milk from cows free of intra mammary infection: III. Pulsator rate. Journal of Dairy Research, 50, pp 149-152.
8. Reneau, J.K. 1986. Effective use of Dairy Herd Improvement somatic cell counts in mastitis
control. J. Dairy Sci. 69:1708.
9. Kitchen 1981; Harmon 1994. Handbook of Milk Composition 261.
10. Politis i Ng-Kwai hang, 1998. Effects of somatic cell count on quality and shelf-life of pasteurized fluid milk.
11. Harmon, R.J. (1994) Pysiology of mastitis and factors affecting somatic cells counts J.Diary Sci. 77, 2101 - 2112.
12. Kroeker, E.M., Ng-Kwai-Hang, K.F., Hayes, J.F., Moxley, J.E. Effect of jff-lacto globulin variant and environmental factors on variation in the detailed composition of bovine milk serum proteins. J. Dairy Sci. 1985;68:1637-1641.
13.Grandison, A.S. and G.D. Ford, (1986). Effects of variations in somatic cells count on the rennet coagulation properties of milk and on the yield composition and quality of Cheddar cheese. J. Diary Res. 53: 645 - 655
