Effects of Pasteurization on the Nutritional Quality of Milk

Milk is a rich source of vitamins, proteins and minerals which are important nutrients for the human being. Pasteurization, a kind of moderate heat treatment, definitely causes some damage to the nutrients in the milk although it may possibly guarantee safety for consumption of milk. For instance, HTST pasteurization, the most commonly used processing technique, is processing milk at greater than or equal to 72 o C for greater than or equal to 15 s. The thermal instable nutrient will be damaged by the high temperature heating although with a short time. Milk a significant source of B vitamins, supplying thiamin, riboflavin, niacin, pantothenic acid, vitamin B6, folate, and

vitamin B12. In the recent years, most of the researches were focused on the

vitamins loss during the HTST heat treatments. The FDA contends that the major nutrients remain unchanged by pasteurization, and that thiamin, folate, B12 and riboflavin will experience losses from 0% - 10%. This reduction is

described as “marginal” (Wong 1999; Miller et al., 2000). Figure 1 shows the comparison of vitamin loss due to the UHT and HTST processing. The thiamine, Vc, and B12 was damaged about 10% during the HTST processing

while the other vitamins were not influenced by the HTST treatment. However, the UHT causes much severe reduction to the vitamins due to its high treatment temperature than the HTST, indicating that HTST is an effective method to reserve the vitamins. Riboflavin, another vitamin, is rich in

the milk. It is heat stable and will not be affected by the hear treatment. However, the direct sunlight can cause the decrease of the riboflavin in the milk (Renner, 1986). Thus, the packaging material is a very important aspect to prevent the degradation of riboflavin. Folic acid another important vitamin which promoted the development of marrow cells (Bren et al. 2004) found that pasteurization induced less than 10% loss for the folic acid while the UHT damage more than 50% of the folic acid. They also showed that the addition of ascorbic acid can reduce the loss of folic acid during the heat treatment. Other researchers believed that the concentration of oxygen in the package will affect the loss the folic acid. Presently there is a folate binding protein which assists the intake of folic acid, some researches showed conflicting results about the protein damage during the pasteurization. The explanation of the conflicting results may be the HTST temperature is close to the denaturation temperature of this protein. (Anderson et al. 1994) studied the changes of vitamin B12, folate and ascorbic acid during the storage. They found that there

were no general or appreciable changes in vitamin B12 or folate content during

storage. However, about 25–45% of the ascorbic acid was lost during storage. The levels of fat soluble vitamins, such as VA, VD and VE in the milk, were

slightly affected by the pasteurization processing due to the protection of the fat globules. In short, pasteurization temperature does not affect fat-soluble vitamins (A, D, and E), as well as the B-complex vitamins riboflavin, pantothenic acid, biotin, and niacin. The losses of vitamins are considered lower than those that take place during the normal handling and preparation of foodstuffs at home (Lund, 1982).

Figure 1. The vitamin loss due to the UHT and HTST processing. (Dairy Management Inc., 2003; Wong, 1999; Miller et al., 2000).

Thiamine Vc B1 B6 B9 B12 10 12 14 16 18 20 L o ss (% ) Vitamins UHT HTST

As it is well known, milk is an excellent resource of high biological value proteins due to the fact that milk can provide all of the essential amino acids that human being need. These essential amino acids can not be produced by the human body and must be ingested from the foods. The pasteurization promotes the Maillard reaction of the milk. The Maillard reaction can lead the degradation of the milk proteins and amino acids, thus reducing the protein quality of the milk. However, when compared with the UHT processing, the HTST processing causes much less reduction of the protein quality. (AlKanhal. 2001) pointed that this reduction in nutritional quality might be significant for children who are solely dependent on this type of milk in their diet. To some extent, heat treatment may denature milk proteins. This effect is not considered a disadvantage from the nutritional point of view because it only changes the specific arrangement of the casein. Since there are no breakdown of peptide linkages casein can be considered a thermal-resistant protein. Although α-lacto albumin is relatively heat stable, other whey proteins can be denatured by heating. These denatured proteins becoming more digestible than their naturally form in the milk because the protein structure is loosened and digestive enzymes can break them down easier (Renner, 1986). Milk contains a lot of antibacterial proteins (e.g.) lactoferrin, which binds free iron effectively limiting its availability to pathogens for growth, which is not affected by standard pasteurization techniques. Although ultra-pasteurization (UHT) does reduce its ability to bind free iron, bacteriocins and lysozyme, are not affected by pasteurization. Another milk protein, lactoperoxidase, contributes to the antibacterial properties of milk by catalyzing the production of hydrogen peroxide. Lactoperoxidase retains 70% of its activity and is heat stable even after pasteurization.

In addition, the pasteurization does not impair the nutritional quality of milk fat, calcium, and phosphorus (Beddows & Blake, 1982). The mineral of milk is rich and changed slightly during the pasteurization processing. Despite the fact that pasteurization may slightly reduce the amount of free calcium in the milk, both the total amount of calcium and the bioavailability of the calcium in milk remain unchanged after pasteurization. The iodine content of milk varies greatly, depending on the cow's condition, in some instances a 20% reduction in iodine has been reported with pasteurization. Furthermore, milk contains a large amount of lactose, about 4.8% to the total mass. Lactose in milk is stable during standard pasteurization; thus, the concentration of lactose in milk is not be significantly affected by pasteurization because the milk contains little alkali. Small amounts of lactose are transferred to the lactulose, a functional disaccharide which is useful to prevent constipation.

Nevertheless, pasteurization will destroy the lactase-producing bacteria that may be present in raw milk, which contribute to greater lactose tolerance. In addition, milk contains a lot of other nutritional components, such as oligosaccharides, lactoferrin, lysozyme, and lactoperoxidase, which are either unaffected or minimally affected by pasteurization. Oligosaccharides, as the bifidus factor binds to pathogens to prevent their adherence to target mucosal receptors, are heat stable. In conclusion, pasteurization does not significantly alter the nutritional value of milk.

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