Microbial Food Spoilage And Its Control Pdf
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Microbiology is important to food safety, production, processing, preservation, and storage. Microbes such as bacteria, molds, and yeasts are employed for the foods production and food ingredients such as production of wine, beer, bakery, and dairy products.
- Food spoilage
- Microbial Food Spoilage — Losses and Control Strategies A Brief Review of the Literature
- Introduction to the Microbiology of Food
- Main Groups of Microorganisms of Relevance for Food Safety and Stability
All food should be safe and free from contamination and spoilage at all points in its journey from its source until it reaches the consumers. However, food contamination is a serious public health problem in Ethiopia, resulting in foodborne diseases that affect many people every year.
Hence, awareness of potential sources of food contamination is an important component of good nutrition and good health. In this study session we are going to concentrate on food contamination by microorganisms, chemicals and physical factors.
Food may be contaminated by different microorganisms or by chemicals that can cause health problems for anyone who eats it. In Study Session 9 you will learn in detail about foodborne diseases. But first you will be introduced to the basic principles of food microbiology in this study session, and about the ways in which food becomes contaminated by different microorganisms, chemicals and physical objects. You will also learn about the causes of food spoilage and its consequences for health.
SAQ 8. Infectious agents are organisms that can be passed to, and between, people in the process of infection transmission.
Many infectious agents bacteria, viruses, fungi and protozoa are microorganisms that are too small to be seen except with a microscope; the adult stages of disease-causing parasites e. Microbiology is the science that deals with the study of microorganisms. Although infections often result in disease, it is possible to be infected with a pathogen and still appear healthy. However, the infectious agent can still be passed on to others, for example by spreading into food handled by the infected person.
The majority of foodborne diseases those caused by infectious agents transmitted to people in the food we eat are due to bacteria, but as you will see in Study Session 9, viruses , parasites and toxins can also cause foodborne diseases. Bacteria are the most abundant of all organisms. Bacteria are unicellular organisms made of one cell and are very small in size, ranging from 0.
Bacteria reproduce asexually. There are pathogenic bacteria capable of causing human illness and food spoilage, but there are also beneficial species of bacteria that are essential to good health and a healthy environment. For example, beneficial bacteria live in our gut and help us digest our food; some bacteria are used to produce foods such as yoghurt and cheese; and others break down wastes in the environment.
Some bacteria are capable of forming highly resistant and endurable structures called spores. Bacterial spores are resistant to heat, freezing, drying, chemicals and other adverse environments. This means the spores can survive the normal processes of food storage and preparation. Two examples of spore-forming bacteria important in food contamination are Bacillus and Clostridium. Temperature, humidity, oxygen and water are important for bacteria to grow and multiply. Under favourable conditions a growing bacterial population can double at regular intervals ranging from about 15 minutes to several hours.
This means that the numbers of bacteria in food can increase rapidly and soon become hazardous to health, particularly if the food has a favourable temperature and water content. In the next section, we look in detail at factors that can promote or delay bacterial growth in our food. The growth of microorganisms in food products can be affected by extrinsic factors and intrinsic factors , as you will see below.
By understanding the factors affecting the growth of microorganisms in food we can know how to keep food safe to eat. This knowledge can also help us to work out how to preserve food for longer. Extrinsic factors are factors in the environment external to the food, which affect both the microorganisms and the food itself during processing and storage.
Extrinsic factors include temperature, humidity and oxygen. Different microorganisms grow over a wide range of temperatures. Some microorganisms like to grow in the cold, some like to grow at room temperature and others like to grow at high temperatures. This is of paramount importance in food safety, because if you know the temperature growth ranges for dangerous microorganisms it helps you to select the proper temperature for food storage to make them less able to grow and reproduce.
The humidity of the storage environment is an important factor for the growth of microorganisms at the food surfaces. If you store food in a dry atmosphere , microorganisms are less able to grow than if the food is stored in a humid moist environment.
Therefore, dry conditions are better for food storage than moist conditions. Many microorganisms need oxygen in order to develop and reproduce: these are called aerobic microorganisms. A good example is Escherichia coli , a faecal bacterium which grows readily on many foods. If you keep food in a low oxygen environment, aerobic bact eria cannot grow and multiply. Conversely, there are some microorganisms that grow without oxygen, called anaerobic microorganisms.
An example of this is Clostridium botulinum , the bacterium causing botulism, which can survive in very low oxygen environments such as tinned foods. Intrinsic factors exist as part of the food product itself.
For example, meat has certain characteristics that may promote the growth of certain microorganisms. The following common intrinsic factors affect the growth and multiplication of microorganisms in foods. Environments that are acidic have pH values below 7; those that are alkaline have pH values above 7. Most microorganisms grow best at close to the neutral pH value pH 6.
Only a few microorganisms grow in very acid conditions below a pH of 4. Bacteria grow at a fairly specific pH for each species, but fungi grow over a wider range of pH values. For example, most meats naturally have a pH of about 5. At this pH meat is susceptible to spoilage by bacteria, moulds and yeasts; however the pH of meat can be lowered by pickling, which makes it less favourable as an environment for microorganisms to grow in.
Microorganisms need a moist environment to grow in. The water requirements of microorganisms are described in terms of water activity represented by the symbol a W , a measure of how much water is present. Most foodborne pathogenic bacteria require a W to be greater than 0. Think of some foods that store well when they are dry but become contaminated quickly when they are wet. You may have thought of different examples: the one that we thought of is rice. When rice is dry it will store for a long time, but when it is cooked and wet it will go bad quite quickly and cause food poisoning.
In order to grow, multiply and function normally, microorganisms require a range of nutrients such as nitrogen, vitamins and minerals. Microorganisms therefore grow well on nutrient-rich foods. The natural covering of some foods provides excellent protection against the entry and subsequent damage by spoilage organisms. Examples of such protective structures are the skin of fruits and vegetables such as tomatoes and bananas Figure 8. Bacteria are a major source of microbial contamination of food, i.
Viruses, parasites and fungi are also able to contaminate food and cause foodborne illnesses in humans. Microorganisms can enter food through different routes. Look at Figure 8. The most common routes of entry are discussed below. Microorganisms are found everywhere in our environment. Many types can be found in air and dust , and can contaminate food at any time during food preparation or when food is left uncovered Figure 8.
Imagine a kitchen where food is prepared and stored in rural communities, and think how easily microorganisms in the air and dust could contaminate the food.
Many microorganisms present in soil and water may contaminate foods. Microorganisms also grow on plants and can contaminate food if care is not taken to remove them by washing or inactivate them by cooking.
Soil is a particularly rich source of Clostridium bacteria. Water may be contaminated by faeces. Plants may also be contaminated by faeces if untreated sewage has been used as a fertiliser. The intestines of all humans and animals are full of microorganisms, some of which are beneficial but others are pathogenic. Bacterial pathogens such as Salmonella, Campylobacter and Escherichia coli strain OH7 are common examples. Contamination of foods by faecal material is the major cause of food poisoning events.
Escherichia coli abbreviated to E. The strain called E. Many foodborne microorganisms are present in h ealthy animals raised for food, usually in their int estines, hides, feathers, etc. Meat and poultry carcasses can be contaminated during slaughter by contact with small amounts of intestinal contents. Animal hides are an important source of contamination of the general environment, the hands of meat worker s, and skinned meat carcasses. Hides are a primary source of E. Hides become contaminated either because the outside of the hide is dirty, or because once removed from the animal, the inside of the hide is a good breeding place for microorganisms.
Animal feeds are a source of microorganisms, especially Salmonella , which can contaminate poultry and other farm animals. The organisms in dry animal feed spread throughout the local environment and may get on to animal hides, hair and feathers, as well as on people who handle the feeds. The term food handler can be applied to anyone who touches or handles food, and this includes people who process, transport, prepare, cook and serve food.
The microorganisms transmitted to foods by food handlers may come from the hides of animals, soil, water, dust, gastrointestinal tracts and other environmental sources. In food preparation at home, foodborne microorganisms can be introduced from the unwashed hands of people who are infected by bacteria and viruses, and who cook and serve the food to family members.
Food utensils are cutting boards, knives, spoons, bowls and other equipment used in food preparation, which may become contaminated during food processing and preparation. For example, in families where there is no access to running water, the food utensils may not be properly cleaned, stored and handled, and may become a major route of food contamination.
Cross-contamination of food is the transfer of harmful microorganisms between food items and food contact surfaces. Prepared food, utensils and surfaces may become contaminated by raw food products and microorganisms. These can be transferred from one food to another by using the same knife, cutting board or other utensil without washing it between uses. A food that is fully cooked can become re-contaminated if it touches raw foods or contaminated surfaces or utensils that contain pathogens.
For example, you should never:. An unsafe temperature for food storage is a major factor in food contamination.
Microbial Food Spoilage — Losses and Control Strategies A Brief Review of the Literature
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Food spoilage is the process where a food product becomes unsuitable to ingest by the consumer. The cause of such a process is due to many outside factors as a side-effect of the type of product it is, as well as how the product is packaged and stored. Due to food spoilage, one-third of the world's food produced for the consumption of humans is lost every year. Bacteria are responsible for the spoilage of food. When bacteria breaks down the food, acids and other waste products are generated in the process. The first type is called Clostridium botulinum and targets food such as meat and poultry, and Bacillus cereus , which targets milk and cream.
Food spoilage and deterioration is no accident. It is a naturally occurring process. To understand how to maintain the quality of food and prevent spoilage, we need to know what can cause it. Factors that affect food spoilage include:. Many types of microorganisms can cause food problems. The microorganisms that can cause food-borne illness are called pathogenic microorganisms.
Introduction to the Microbiology of Food
Part 1 Detection and analysis of food spoilage: Quantitative detection and identification methods for microbial spoilage; Detection, identification and enumeration methods for spoilage yeasts; Detection, identification and enumeration methods for spoilage moulds; Modelling microbial spoilage; Determining the stability and shelf-life of foods. Part 2 Managing food spoilage: Managing microbial food spoilage: An overview; Managing microbial spoilage in the dairy industry; Managing microbial spoilage in cereal and baking products; Managing microbial spoilage in the meat industry. Part 4 Spoilage moulds: General characteristics of moulds; Zygomycetes; Penicillium and related genera; Aspergillus and related teleomorphs; Other types of spoilage moulds.
All food should be safe and free from contamination and spoilage at all points in its journey from its source until it reaches the consumers. However, food contamination is a serious public health problem in Ethiopia, resulting in foodborne diseases that affect many people every year. Hence, awareness of potential sources of food contamination is an important component of good nutrition and good health.
Main Groups of Microorganisms of Relevance for Food Safety and Stability
Bacteria are the most important microorganisms to the food processor. Most are harmless, many are highly beneficial, some indicate the probable presence of filth, disease organisms, spoilage and a few cause disease. There are thousands of species of bacteria, but all are single-celled and fall into three basic shapes: spherical, straight rods, and spiral rods. To see them, you need a microscope that magnifies about fold. All bacteria reproduce by dividing into two cells. The two cells then divide to become 4, 4 become 8, and so forth. Under ideal conditions, this doubling may occur as frequently as every 15 minutes, so that within 5 hours there will be more than a million cells from the original single cell.
Даже за широким кольцом терминалов она почувствовала резкий запах одеколона и поморщилась. - Замечательный одеколон, Грег. Вылил целую бутылку. Хейл включил свой компьютер. - Специально для тебя, дорогая. Он стал ждать, когда его компьютер разогреется, и Сьюзан занервничала. Что, если Хейл захочет взглянуть на включенный монитор ТРАНСТЕКСТА.
ieee-citisia.org Food Research Microbial Food Spoilage — Losses and Control Strategies. A Brief Review of the ninety-six billion pounds of food in the U.S. were lost by retailers.