File Name: microorganisms in milk and milk products .zip
Exploitation of Microorganisms pp Cite as. The manufacture of cheese, yoghurt and other fermented milks and some types of butter depends on the activity of starter microorganisms. The most important of these, are species of Lactobacillus, Lactococcus , Leuconostoc and Streptococcus which form part of a group commonly referred to as lactic acid bacteria LAB. Recently, use of a fifth member, Pediococcus, has been proposed Tzanetakis et al.
The numbered list below identifies seven types of bacteria according to how they change the properties of milk. Often these changes are negative spoilage but as we will see in later sections, many of these bacteria are important to the development of cheese flavour.
Before proceeding to the list, please note the following definitions:. Keeping the above definitions in mind, note the following types of microorganisms, grouped according to their impact on milk quality.
For now note the following:. Most important in cheese milk are species of:. Some examples are:. Toggle navigation. Types of microorganisms and their activity in milk. Before proceeding to the list, please note the following definitions: Psychrotrophic refers to microorganisms which are able to grow at temperatures less than 7C.
Cold milk storage and transport selects for psychrotrophic bacteria which are often proteolytic and lipolytic. Little growth occurs at temperature less than 2C. Spore forming bacteria are able to exist in a highly stable form called 'spores'. In the spore state, these bacteria are able to withstand greater extremes of acidity, temperature and desiccation.
Enzymes are biological catalysts that accelerate the rates of biochemical reactions. Bacterial enzymes are most significant to milk spoilage and cheese ripening but it is important to distinguish between the enzyme and the bacterial source.
For example, many psychrotrophic bacteria produce heat stable enzymes which remain active in milk and cheese even after the bacteria are killed by pasteurization.
For now note the following: As noted earlier, LAB are able to readily metabolize lactose so they have some competitive advantage over other microorganisms. Notwithstanding, their ability to metabolize lactose, LAB prefer temperatures greater than 30C, so, depending on initial relative counts, psychrotrophic bacteria including some coliform and pseudomonas bacteria are able to outgrow LAB at room temperature. Yeasts are always present in milk and are common contaminants during the cheese making process.
They may cause 'yeast slits' in cheese and contribute to ripening of surface ripened cheese. Coliform bacteria are always present in milk but their numbers can be minimized by good sanitation. Also, coliform bacteria compete poorly with lactic acid bacteria, so their numbers rapidly decrease in the presence of a rapidly growing lactic acid culture. The resulting craters and cracks in the cheese are called 'late gas defect'.
Five hundred spores per litre of milk are sufficient to cause late gas defect. Some lactic cultures, called heterofermentative, also produce carbon dioxide. Printer-friendly version.
June 1 is World Milk Day: a good reason to take a closer look at this tasty drink, which is very nutritious, but also an ideal breeding ground for harmful microorganisms. In recent years, milk has been quite discredited: It has been said that milk makes people sick, fat and tired. Many people have reduced their milk consumption due to health or ethical reasons. Nevertheless, milk contains numerous valuable nutrients. Milk substitutes such as soy, rice or almond milk usually contain much fewer nutrients. Manufacturers perform various tests in order to ensure that the milk reaches consumers in good order and condition.
The dairy products industry is going toward safe milk and its products in the food market. The aim of this work is focused on milk microbial contamination and its impacts on milk production and dairy industry with their implications in milk product quality, food-borne diseases from raw milk, and unpasteurized milk by food-borne pathogen microbial contamination and milk and dairy product spoilage. The microbial milk contamination source comes from herd hygiene and health status, mastitis prevalence, production environment, and milking parlor and milk conserving practices in dairy farm. Moreover, these facts are implicated in milk quality and milk spoilage and unsafe dairy products. The milk production system and the dairy plant operations keep track in pasteurized milk and fresh dairy products reviewing the traceability in field situational diagnosis report.
Authors: H. Michael Wehr and Joseph F. View Chapters. Frank , PhD. Technical Committee. Consensus Reviewers. Chapter 1 Standard Methods.
PDF | Milk is a good source of nutrients and edible energy, not only for mammals but also for numerous microorganisms that thus can grow in.
Milk Sours Chemical Or Physical
Microbial spoilage of milk and milk products Contamination of milk: Contamination of milk occurs at two levels: On farm: Freshly drawn milk contains relatively few bacteria however Micrococcus and Streptococcus are usually found in aseptically drawn fresh milk. During normal milking process, milk is subjected to contamination from udder of animal and adjacent areas. Bacteria found in manure, soil and water contaminate are udder of animal from where they enter into the milk. Other possible source of contamination is hand and finger of milker or other dairy workers.
Altekruse, S. Emerging Foodborne Diseases. Stern, P.
Metrics details. Milk being a suitable medium for bacterial growth, it can serve as a source of bacterial contamination. However, there are few studies that examined the health hazards of raw milk consumption in Ethiopia.
The numbered list below identifies seven types of bacteria according to how they change the properties of milk. Often these changes are negative spoilage but as we will see in later sections, many of these bacteria are important to the development of cheese flavour. Before proceeding to the list, please note the following definitions:. Keeping the above definitions in mind, note the following types of microorganisms, grouped according to their impact on milk quality. For now note the following:.
Raw milk is milk that has not been pasteurized to kill harmful bacteria. It can come from any animal. Raw milk can carry dangerous germs, such as Brucella , Campylobacter , Cryptosporidium , E.