Pasteurization is a process that involves heating of raw milk to a certain temperature within a given set of time. This process kills harmful bacteria found in unpasteurized milk, for example, Salmonella, Listeria and E coli responsible for food borne illnesses. These bacterial organisms are responsible for human diseases such as Typhoid, diphtheria, Listeriosis and tuberculosis. The process was first initiated by Louis Pasteur in the year 1864. Pasteurized milk can stay for a certain period without refrigeration. However, refrigeration especially after opening the seal, is still necessary because of some nonpathogenic bacteria that because food spoilage and is non-receptive for heating.
Researchers and academicians have invested a lot of time in eliminating certain myths that have haunted this process. According to conducted research, pasteurization does not reduce the nutritional value neither does it protect those individuals who are allergic to lactose as the society has been induced to believe.
Process of Pasteurization
There are two major methods used in Pasteurizing milk; traditional pasteurization and ultra pasteurization. Traditional pasteurization involves heating milk for a period of 15 seconds to a minimum temperature of 1610 F. This process enables milk to last for a period of 16-21 days from the date of packaging. This process is also referred to as High Temperature Short Time (HTST) pasteurization.
On the other hand, Ultra pasteurization is also referred to as Ultra high temperature (UHT) pasteurization. This is an advanced method that has been appreciated by many dairy products industries in the world. Ultra pasteurization heats milk up to 2800 F for a period of two seconds. It is more efficient because it kills a higher proportion of harmful bacteria than HTST method.
Steps for Pasteurization
Step 1: Raw milk, usually at 39.20 F is put into a pasteurizing machine
Step 2: It passes through a plate heat exchanger .It passes through subsequent chambers where cold milk is pumped into the first chamber while the milk that has been heated and pasteurized is pressured into the next chamber. Heat that has been generated from the hot milk is passed to the cold milk through the steel plates. In this section, the temperature of the milk rises to a range of 134.5 to 154.4 degrees Fahrenheit that is equivalent to 57-680 Celsius.
Step 3: Milk is passed to the heat exchanger through the plate’s .In this section; hot water in the second chamber heats the milk to a temperature of 16.5 degrees Fahrenheit, equivalent to 72 degrees Celsius. This is the temperature for HTST pasteurization.
Step 4: Hot milk is passed through the holding tube for a period of 15 seconds. After this tube, the milk has attained the pasteurization section.
Step 5: Before the milk is packaged, it is passed back through the re-generative section to warm the cold milk that has just been pumped into the pasteurization chamber. During this process, the hot milk looses temperature to the cold milk and to a level of 89.60 F (About 320 Celsius)
Step 6: This is the section where the pasteurized milk is cooled through a coolant to 39 degrees Fahrenheit. This is the final stage and the milk is ready for packaging.
Molecular difference between denaturation and coagulation of proteins
Coagulation refers to the chemical change in the structural form of protein from a liquid to a solid. On the other hand, denaturation is a process that involves disruption of the secondary and tertiary structure of a protein compound. It transforms a protein into a different shape. Denaturation occurs through application of an external compound that alters the structural bonding of amino acids. Such forces include acids, alkali or heating.
Denaturation is the subject of coagulation and, therefore, occurs first. During the denaturation, hydrogen bonds break and alter the structure of the protein. The protein molecule unfolds occupies a less compact structure than its original state. When protein molecules unfold, they bump into other protein molecules and bond to become solid. Most proteins when denatured cannot be reversed into their normal shape. For instance, when an egg is fried, it cannot regain its original shape. However, other protein compounds can regain their original shape a process called renaturation
In the quaternary structure, the arrangement of protein molecules is disrupted and leads to separation of its bonding. Covalent interactions between the polar amino acid chain distorted. This leads to an irregular pattern of protein molecules that creates room for coagulation. However, the sequence of amino acids held by covalent bonds of peptides is not affected by denaturation
Describe what happens to the casein proteins in milk during the steps used above.
Casein is the main protein in milk .It is a phosphoprotein composed of phosphates attached to hydroxyl groups of amino acid chains. It exists in milk in a form of calcium salt called calcium caseinate. It is a mixture of three proteins that include alpha, beta and kappa caseins that form a mecille. One of the processes of denaturing proteins is heating. When milk is heated to about 400 Celsius, milk is denatured into curds. When acetic acid is added to adjust the pH level, casein protein clots and precipitates out with the butterfat. This leaves a liquid component called whey. When no casein proteins stop to disassociate, the liquid turns from milky to clear
Three ways we can denature proteins and which food products these techniques would be used to for denaturing proteins.
Thermal denaturation: This involves increase of temperature above the isoelectric point through heating
pH denaturation: This involves the addition of an acid or an alkali.
Change of ionic strength: proteins have been discovered to be more soluble to pure water than pure water.Salt particles bond with oppositely charged protein molecules.This increases hydration on proteins. This deters change in solubility.
Food products include eggs, milk, and wheat and soy products
References
Roberts, M., Reiss, M. J., & Monger, G. (2000). Advanced biology. Walton-on-Thames: Nelson.
Fandel, J., Wilson, K., Ramos, R., & Barnett, C. (2007). Louis Pasteur and pasteurization. Mankato, Minn: Capstone Press.
Lau, K. Y., Barbano, D. M., & Rasmussen, R. R. (2001). Influence of Pasteurization of Milk on Protein Breakdown in Cheddar Cheese During Aging1. Journal of Dairy Science.
Anson, M. L., & Mirsky, A. E. (2000). PROTEIN COAGULATION AND ITS REVERSAL : SERUM ALBUMIN. The Rockefeller University Press.
