The Technologies Used for the Heat Treatments of Milk - Essay Example

Milk Treatment xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Effects of heat treatment xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Name xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Institution xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Lecturer xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Date Raw milk is milk in the natural form. It can be a source of bacteria that cause diseases like undulant fever salmonellosis, tuberculosis and dysentery. It also contains many disease producing organisms when in this form. Different heat and treatments are given to raw milk removes pathogenic organisms. This increase the shelve life of milk. Heating, if done inappropriately can cause changes in the constituents of milk, like affecting the solubility and the nutritional value of the milk (Morales 2000). There are heating criteria used on milk which must guarantee the correctness of heat treatment which comply with the correct standard and terms of processing milk like thermization, pasteurization and sterilization. Nowadays, there are two main heat treatments used on milk, namely, Ultra heat treatment (UHT) allowing longer periods of time like 2 – 3 months without refrigeration and pasteurization allowing a shorter period of less than 21 days with refrigeration. However, there are technologies developed to obtain pasteurized and UHT milk using different temperature profiles and the effect of the quality of milk may vary depending on the process involved and temperatures applied (Birlouez – Aragon et al 2002). Intense heating of milk can cause destruction on vitamins, like vitamin C which is heat labile. The two most stable pathogens in milk are Mycobacterium that causes tuberculosis and coxiella burnetti that causes Q fever. To kill this bacterial there has to be a minimal degree of temperature and duration. To ensure high quality of milk these temperature and time combinations are highly regulated. The higher the temperature utilized the shorter the time required destroying all pathogenic microbes. Heat treatment on milk involving heating it to 72C with a holding time of 15 seconds before it’s cooled is called high temperature short time treatment (HTST) mode of pasteurization. This occurs when milk is brought to a temperature of 72C to 15 seconds; it is then cooled to 10 C or below. This temperature and time give a better margin of safety. Heating is usually done by hot water and heat exchange is done through stainless steel plates by passing the milk through the annular space which is between the concentric water heated tubes. In HTST pasteurization, little piping is used to avoid superheating of milk. This is done by allowing milk to flow over a water heated surface which is larger than the amount of milk heated, and it is kept at a temperature not greater the 15 higher than required heating on milk. The hot surface is heated by contact with hot water; no live steams come into contact with the surface. A thermostat is used to keep the temperature uniform. The temperature is automatically controlled to ensure accurate heating on milk for accurate results. This ensures that all micro organisms capable of causing deceases are killed. HTST pasteurization is effective in destroying various bacteria of pathogenic species causing diseases (Green et al 2002). More over the use of HTST allows total destruction of several microbial growths and inactivate the enzymatic activity. The shelf life of milk treated is from 2 days to 16 days. This is dependant to the quality of the raw milk and the degree of refrigeration. This method of pasteurization ensures that the original taste of the milk is maintained and also ensures minimal denaturarization of proteins and bioactivity reduction; maintaining the value and quality of milk. However, mycobacterium avium paratuberculosis (MAP) survives the 72C and 15 seconds heating. This therefore lowers the quality of milk for it puts the consumers at risk. HTST pasteurization hardly changes the milk contents, but milk cannot be kept for a long time. This is because the high pasteurization temperatures stimulates pole of bacteria to grow. There are also other methods of pasteurization encompassing longer time regime, like the 92c for 10 minute which is an older method this ensures that any microorganism that can survive the 72C temperature has no chances of survival and being in the milk. More over, there can be the use of higher temperatures in short time flames, like the 125C to 2 second method. This is referred to as flash pasteurization. Different enzymes present in milk have different levels of heat destruction. In pasteurization different time and temperature are used to ensure a reduction in microorganisms. Heat treatment of 143C and 5 seconds lies in the class of ultra high temperature (UHT). UHT milk is sterile not pasteurized and therefore it has long shelf life if stored at room temperature and not opened. Milk processed through this way undergoes through a continuous flow operation that is done through a closed system to prevent it from airborne microorganisms’, killing every micro organism that destroys the milk. Then it passes through heating and cooling stages in quick sessions. And packaging is done through aseptic packaging to protect the product against light and atmospheric oxygen; Ambient storage. Due to a powerful heat exposure, all micro organisms are killed making it good for human consumption anytime. When milk is subjected to such heat it becomes commercially sterile and can be packaged in air tight containers. UHT treatment uses two methods which depend on the desired quality level of milk; direct and indirect heating. Direct heating, the milk is brought in to contact with hot steam under strictly controlled conditions. After the sterilization temperature of 143C for 5 seconds is reached, the temperature is lowered by flash cooling vacuum vessel. The rapid heat and cooling gives minimal heat load on milk resulting to high quality sterile milk. In the case of indirect heating, there are partitions, when the hot medium is flowing in one partition the milk is flowing in another. Then heat is transferred to the milk without direct contact between the hot medium and the milk. Cooling is done in the same procedure. UHT milk remains fresh without refrigeration and can remain safe for drinking for months, but after opening, refrigeration as required for HTST treated milk is applied. However, since the temperature used is high, the cooked flavor is present, brown color in milk is limited and denaturing of proteins is high. UHT treated milk results to decrease of proteins fats and total solid contents of milk. This is attributed to the moisture loss of milk moisture content during heat treatment. There is usually a loss of up to 95% in moisture content of milk during heat treatment (loker et al 2003).This lowers the quality of milk. The sterilization and heating in UHT leads to over processing and loss of product quality. However there are also the present of heat resistance proteases which affect the stability of UHT milk. Contaminations of milk also occur during the extraction from the animal. To avoid this, 90C for 10 minutes temperature is used for cleansing equipments with live steam. Lack of hygiene can contaminate milk with other types of bacteria turning it sour and reducing the storage life. A healthy cow is able to protect milk while it is in the udder, but contamination is likely to occur when hygienic procedures are not followed when milking. Bacteria can develop in milk reduces remaining in the milk equipments. Improper cleaning and drying will allow them to contaminate milk. The ways that the milking equipments are handled affect the quality of milk. Sterilizing these equipments is highly recommended to ensure that the milk is not contaminated before it is heat treated. All equipments are subjected to a 90C for 10 minutes temperatures to ensure that all remains of milk and bacteria are destroyed. This sterilization is highly effective when they are placed in a cabinet for treatment when they are either dismantled or not. These utensils must be immersed totally to ensure total sterilization. Heat treatment on milk causes irreversible changes in milk protein structure. When milk is heated at temperatures above 65C whey protein unfold and expose previously hidden hydrophobic groups (Croguennec, Kennedy and Mehra 2004). Due to unfolding the whey proteins interact with themselves and casein to form heat induced proteins (Danto, Guyomarch, Amoit, and Daglesih 2007). These changes affect the protein functionality which can be detrimental (Creamer and Singh 1992).This results to denaturalization of proteins interfering with the quality of the milk. Lactose is another major carbohydrate of milk. Lactose undergoes tremendous change during heat treatment. This happens between amino groups of proteins and aldehyde groups of lactose resulting to maillard reaction. Maillard reaction is initiated during heat treatment and continues during storage causing degradation of proteins. The quality of UHT milk decreases during storage and therefore the in vitro digestibility of proteins in UHT treated milk are more impaired comparing to HTST pasteurized milk (Carbonaro 2000). Folate binding proteins are present in raw milk and they assist in the uptake of folate in the intestine, but this reaction is great in temperatures above 100C, which result in color and flavor and also loss of essential amino acids. Heat treatment on milk is done to kill all the bacteria in milk. However, Elzubeir et al. (2007) found out that low pasteurization, high pasteurization and UHT do not completely destroy all the bacteria present in milk, and they continue increasing during the storage period. This increases the risk due to the availability of this milk in the ready market. Any heat on milk exceeding 90C causes degradation of proteins and co-aggregates increasing their solubility. Lipolysis is caused by the action of lipase enzymes, normal HTST does not brake down this enzyme and therefore they continue to breakdown the fats and release fatty acids during the milk’s storage period (Dairy handbook 1996). When lipase affects the fat triglycederies, free fatty acids and mono – diglycerides are formed. This formation caused the milk to have poor steam frothing properties and cream separation difficulties (Deeth and Fitz –Gerald 1995). Therefore heat treatments on milk affect the quality and the original form of milk components. HTST rarely alters the micro flora of milk. This calls for extreme prevention of the spoilage organisms and pathogens capable of glowing at low temperatures. Bacteria like bacillus get destroyed by pasteurization but the spore form of it is heat stable. If given the correct condition it can continue to grow in pasteurized products. Thus the shelf life of HTST treated milked is greatly reduced. There are spoilage organisms that are capable of contaminating the milk after pasteurization (Harding 1995).this calls for a storage method that will inhibit the growth of this bacterium. The only way of reducing the number of bacterial spore in milk is by increasing the temperature involved in pasteurization. This is done by employing 125C for 2 seconds. However, this heating induces flavor changes that affect the consumer appeal to the product. Heat treatment is used to reduce the number of phychrotrophic gram – negative bacteria in milk, which cause milk spoilage, but it leaves some of the heat resistant microorganisms that slowly grow to an extent of spoiling milk in its storage period (Harding 1995; Nelson 1981). In this case a more temperature and less holding time are applied in milk; to avoid denaturing of the milk nutrients are used. HTST treated is that milk treated with less than 134C heat. Milk treated through this method records unchanged calcium absorption. Vitamins A and D, riboflavin and niacin are also not affected by heat. This means that they are present in pasteurized milk as well as raw milk. However, Thiamine and vitamin B12 are destroyed thus heat treatment on milk still destroys some milk components affecting its quality and value. Heating above 130C causes many damages in milk. When a lot of heat is applied in milk, the milk sugar becomes scorches, casein and albumin are hardened, calcium and magnesium and phosphoric salts are precipitated. This interferes with the cream line. However even if heating using lower temperatures has many advantages, heating at higher temperatures is preferred for it ensures that many disease causing organisms are destroyed. In pasteurization, milk can also be put in bottles and when it is raw and sealed. Those bottles are subjected to a shower of hot water. After heat holding for a certain time they are the cooled by cold water. In this method, the bottle and its cap are pasteurized as well as the milk is being treated. However, this method has its limitation like extra expenses involved, and that an offensive odor that can be present in raw milk has no chance of escaping during heating. Heat treatment on milk also involves the holding method which is used to heat milk at a temperature below 100C and holding time for 30 minutes. Sterilization involves heating milk at a temperature of 110 – 192C and holding time of 20 – 40 minutes. This is done to kill all organisms and help keep milk for a long time without refrigeration. When heat is induced on milk, this makes it less harmful to the consumer for it has no deceases causing micro organisms. Heat treatments on milk are highly recommended. However, when temperatures are increased during treatment, off flavor occur which are caused by volatile sulfur compounds; the reaction caused by the reaction between sugar and protein constituents. This changes the color and the taste of milk. For effective heat treatment on milk, temperatures/time relationship that is above minimum is required. In order to improve the quality of drinking milk, higher temperatures are recommended so as to improve on the destruction of bacterial load on milk. However, many nutrients are destroyed in this process. Human conception of this milk results to deficiency of the required nutrients in the milk some which is brought about by heat treatment on milk. Heat treatment on milk is said to inactivate lipase, temperatures combination of 75C/15seconds inactivates 90% of the enzyme present in milk, and the remaining 10% can produce off-flavor after 2 days. Many people are put of by this. Therefore pasteurized milk, which is heat treated to improve on the shelf life is also not a quality one. When temperatures are induced in milk for the purposes of treatment, calcium and phosphorus are affected. When temperature equal to or below 80C are applied, Calcium and phosphorous is insignificantly reduced, but when the temperatures increase, this causes a tremendous reduction of phosphorus in milk. This is caused by the changes caused by fire on insoluble salts containing the two minerals. Milk which is heated requires to be sterilized. To achieve this filled bottles with milk are put on conveyor belts and carried through steam pressure and emerge after 10 to 30 minutes having being subjected to temperatures ranging from 95 and 120C. Cooling then takes place using cold water tanks, sprays or atmospheric cold air. They are then packed and stored refrigerated ideally below 6C and once opened it must be used within five days. This improves the storage life of milk. Heat treatment in milk in common in many countries in the world but unfortunately it robs the nutritional value of milk. In series of experiments conducted show that the nutritional value of heat treated milk is low compared to raw milk. Experiments did on heat treated milk show a slight loss of protein, calcium, the phosphorous, Vitamins A and D and most of B vitamins e.g. Pyridoxine, nicotinic acid, pantothenic acid and biotin. But this cannot be compared with the advantages that come with heat treated milk like the loss of micro organisms causing various deceases. However, farm management also causes vitamin A content especially in some northern countries due to the feeds given to cows during winter. Conclusion Heat treatment results to degradation, denaturation and inactivation of labile components and also formation of other substances which were not present in unprocessed milk. Biologically active agents only preserve them selves only when the milk s in it raw state. Heat damages them but this depends on the intensity of the heat and the time taken to heat milk. A lot of temperatures affect the absorption of some minerals including calcium, iron and zinc through the denaturing of the proteins that transport them. it also affects the bond between proteins and folic acid reducing its absorption, while its an important mineral especially in pregnant women whereby it help prevent nerve damages such as spondyloschisis of the infant. Short heat treatments depletes the overall antioxidant properties of milk (Calligaris et al 2004).Heat treatment decreases the antioxidation capacity of casein (Taylor and Richardson 1980). High temperature heat treatment causes a change in the structure of casein and bioactive peptides. Dephosphopeptides of casein by heat changes not only its structure but also the content of the phosphopetides, thus reducing or completely eliminating its capacity to transfer minerals. When high heat is induced, the digestion of enzymes reacts with the structurally changed proteins as if they were unnatural substrates. Extreme heating of milk results to the creation of inter and intermolecular covalent bonds which resist the hydrolytic enzymes. This promotes the racemic conversion of L-amino acids to D-amino acids which leads to indigestible peptide bonds. The hazardous consequences associated with the untreated milk. Untreated milk hosts very many microorganisms that can cause some of the most killer diseases; it can not be kept for along time and has not been subject to recognized health standards. Therefore despite the milk components interferences associated with heat treatment, its advantages are not worth comparing. References. Morales, F.J., Romero, C., Perez, S.J., 2000: Characterization of industrial processed milk by analysis of heat-induced changes, International Journal of Food Science and Technology, 35, 193-200. Birlouez-Aragon, I., Sabat, P., Gouti, N., 2002: Anew method for discriminating milk heat treatment, International Dairy Journal, 12, 59-67. Green, L., S. Godden, and J. 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