Milk is the lifeline of babies. Milk contains the necessary nutrients needed for growth and development. Milk can also cause death.
Bacteria in Milk
We may not be able to see, smell or taste them. Yet bacteria grow in mild temperatures and can survive in milk carton even after refrigeration. These bacteria thriving in mild can be studied well with the use of the digital binocular microscope.
Beneficial vs Harmful Bacteria
As carefully monitored with the use of the microscope especially the digital binocular microscope, not all bacteria are harmful. Bacteria have many beneficial uses. In milk products, bacteria are useful in the production of yogurt, cheese and related products. Bacteria are utilized to ferment milk for milk products.
Bacteria are likewise harmful. Statistics indicates that there are approximately 450 deaths, 100 stillbirths, and 1,700 serious illnesses in the U.S. yearly which can be attributed to bacteria growing in milk cartons. A study was conducted by Sajid Alavi, an agricultural and biological engineering graduate student on microbial growth in milk.
What is Microbial Growth?
Microbial growth refers to the growth of pathogenic bacteria. These bacteria can cause harmful diseases.
Listeria monocytogenes in Milk
The pathogen Alavi is most concerned about is Listeria monocytogenes. After a thorough examination with the aid of the digital binocular microscope Listeria monocytogenes is known to be the cause of listeriosis, a disease which attack children, pregnant women, and the elderly. It is a form of meningitis. It is likewise described as brain fever which accounts for approximately 40 percent fatality rate. The bacteria come into milk through infected cows.
The standard way for preserving milk is through pasteurization. Milk can be sold up to 14 days after pasteurization. As usually practiced in homes, a carton of milk may just be kept in the refrigerator for a couple of days to over a week beyond that selling date. Under these circumstances, the bacteria are given the chance to multiply.
The optimal temperature conducive to the growth of Listeria monocytogenes is 35 degrees C or 95 degrees F. A closer examination with the use of the digital binocular microscope revealed that Listeria monocytogenes can survive even at a temperature as low as four degrees C or 39.2 degrees F. This temperature is on the cool side for a normal refrigerator. Since these bacteria can survive and grow even at very low temperatures where majority of other bacteria cannot grow, this is a grave concern for dairy milk products.
Experiment on the Prediction of Listeria monocytogenes in Milk
A mathematical model was created which will help predict the growth of Listeria monocytogenes inside a milk carton. To get the necessary data, a colony of bacteria cells was added to a broth of nutrients and water. This makes possible the first step in creating an all-night culture. The following morning, a milliliter of the broth was added to sterilized milk. Regular samples were then taken at varying temperatures and examined under a microscope for bacterial growth. With the collection of data at regular intervals, Alavi was able to write mathematical equations describing the association between growth rate and temperature.
A commercial software program called ANSYS was used in the analysis of the data which traced the heat transfer inside a cardboard milk carton. Combining the microbial growth equations with those for heat transfer, a dynamic model of bacterial growth was created.
Study shows that when introduced into the milk, Listeria monocytogenes experiences a lag period where it takes time to adapt to its new environment. After the lag period is the exponential growth. When the cells are competing for nutrients, growth levels stop for a stationary period. Many cells die because of the lack of sustaining nutrients. At 25 degrees C, it takes approximately 20 hours for the cycle to take place. At four degrees, it takes about 30 to 40 days. It is important to store milk products at low temperature levels.
The scientists believe that this new model will provide dairy industry easier way to test samples before milk is sold to the consumer. Plating is the technical term used for testing for bacteria. It is also time-consuming and expensive. The new model could also set the standards for the future designs in refrigeration apparatuses for the dairy industry.
The Importance of Milk
Milk is a good source of calcium for the bones. Despite the fear of listeriosis people should be advised to continue drinking milk. The Food and Drug Administration regularly checks on the milk supply. Should there be problems, the FDA will recall products from the market.Read more on this topic