FOOD MICROBOLOGY I
Introduction and source of contamination Introduction . Food microbiology is the study of food micro- organisms; how we can identify and culture them, how they live, how some infect and cause disease and how we can make use of their activities.
History . The period that food was gathered: one billion B.C.-8000-10.000 BC . The period that food was produced: 8000-10.000 BC . Beer production: 5000-7000 BC (Babylon) . Milk, cheese, butter: 3000 BC (Egypt) . 1000 BC: Roman people used snow for preserving seafood. . 943 AD: First large food-borne outbreak in history (Ergotism / Claviseps purpurea-rye) History . 1658, A. Kircher: He suggested that there were some invisible worms in spoiled meat, milk etc. . 1765, Spallanzani: He demonstrated that meat broth boiled and maintained in a closed jar did not spoiled. But some people rejected this idea and they suggested that organisms died due to airlessness. . 1837, Schwan: After Spallanzani, he sterilized the air and let to enter the closed jar. And then showed that boiled meat did not spoil. . 1809, Nicolas Appert: Appert had successfully preserved some foods by placing them in glass bottles, which were closed loosely and immersed in hot water. . 1860, Louis Pasteur: He firstly applied heating to destroy the undesirable microorganisms in beer and wine. (Pasteurization)
Relations between food and microorganisms . Is the presence of microorganisms in food normal? . Can you think of foods that do not have any microorganisms? . Why is it important to determine the presence of microorganisms in foods? . Why do we need to determine the presence/counts of microorganisms in foods? Microorganisms in foods . Bacteria . Fungi (Molds and yeasts) . Protozoa . Viruses . Prions (?) (Bovine spongiform encephalopathy (BSE), commonly known as mad- cow disease (MCD), is a fatal, neurodegenerative disease in cattle, that causes a spongy degeneration in the brain and spinal cord.)
1. Bacteria . Prokaryotic organisms. . Taxonomic groups in foods: . Gram (-) aerobes . Gram (-) facultative anaerobes . Rickettsias . Gram (+) cocci . Gram (+), endspore-forming rods . Gram (+), nonsporulating rods . Functional groups present in foods: . A) Based on metabolism . Lactic acid bacteria . Acetic acid bacteria . Propionic acid bacteria . Butyric acid bacteria . Proteolytic bacteria . Lipolytic bacteria . Saccharolytic bacteria . Gas-producing bacteria . Coliforms
. B) Based on response to the environment . Thermophilic bacteria . Psycrophilic bacteria . Thermoduric bacteria . Halophilic bacteria . Halotolerant bacteria . Acidophilic bacteria . Acidoduric bacteria 2. Fungi . Eukaryotic organisms with rigid cell walls that lack chloroplasts. . Cell size: >10 µm . Yeast and molds . Yeasts: mostly unicellular . Molds: multi-cellular and differentiated filamentous fungi.
3. Protozoa . Eukaryotic organisms without rigid cell walls that lack chloroplasts and are quite motile. . Unicellular in at least one life stage. . Cell size >10 µm . Four groups: . Ciliates . Amoebas . Flagellates . Sporozoa 4. Viruses . Obligate parasites. . Size: 0.1 µm . Replicates inside of the host’s cell by producing multiple viral particles.
Sources of contamination All organic compounds → Cell structures + energy + inorganic (Carbohydrates, proteins, lipids compounds (nitrates, sulphates etc.) etc.) 1. Plants and vegetable products 2. Animals 3. Sewage 4. Soil 5. Water 6. Air and dust 7. Food workers (personnel in food processing plants) 1. Plants and vegetable products . The natural surface flora of plants varies with the plant but usually includes species of Pseudomonas, Alcaligenes, Flavobacterium, Micrococcus. Bacillus species, yeasts and molds also may present. . The numbers of bacteria will depend on the plant and its environment. . The numbers of bacteria may range from a few hundred or thousand per square centimeter of surface to millions. . For example; the surface of a well washed tomato may show 400-700 microorganisms per centimeter square, while an unwashed tomato would have several thousand. . Exposed surfaces of plants become contaminated from soil, water, sewage, air and animals, so that microorganisms from these sources are added to natural flora.
2. Contamination from animals . Sources of microorganisms from animals include the surface flora, the flora of the respiratory tract and the flora of gastrointestinal tract. . The natural surface flora of meat animals usually is not as important as the contaminating microorganisms from their intestinal or respiratory tracts. . However, hides, hooves and hair contain not only large numbers of microorganisms from soil, manure, feed and water but also important kinds of spoilage organisms. . Feathers and feet of poultry carry heavy contamination from similar sources. 2. Contamination from animals . The skin of many meat animals may contain micrococci, staphylococci and beta-hemolytic streptococci. . Staphylococci on the skin or from the respiratory tract may be found on the carcass and then on the final product. . The feces and fecal-contaminated products of animals can contain many enteric microorganisms, including Salmonella. . Salmonellosis in animals can result in contamination of animal products and thus contaminate foods derived from them with Salmonella.
3. Contamination from sewage . When untreated domestic sewage is used to fertilize plant crops, there is a likelihood that raw plant foods will be contaminated with human pathogens, especially those causing gastrointestinal diseases. . In addition to pathogens, coliform bacteria, anaerobes, enterococci, other intestinal bacteria and viruses can contaminate the foods from these sources. . Natural waters contaminated with sewage contribute their microorganisms to shellfish, fish and other seafood. 4. Contamination from soil . The soil contains the greatest variety of microorganisms of any source of contamination. . Not only numerous kinds of microorganisms but also large total numbers are present in fertile soils, ready to contaminate the surface of plants growing on or in them and the surface of animals roaming over the land. . Soil dust is whipped up by air currents, and soil particles are carried by running water to get into or onto foods. . The soil is an important source of heat-resistant spore-forming bacteria. . Yeasts, molds and species of bacterial genera Bacillus, Clostridium, Enterobacter, Escherichia, Micrococcus, Alcaligenes, flavobacterium, Chromobacterium, Pseudomonas, Proteus, Streptococcus, Leuconostoc and Acetobacter.
5. Contamination from water . Natural waters contain not only their natural flora but also microorganisms from soil and possibly from animals or sewage. . Surface waters in streams or pools and stored waters in lakes and large ponds vary considerably in their microbial content. . Ground waters from springs or wells have passed through layers of rock and soil to a definite level; hence most of bacteria, as well as the greater part of other suspended material, have been removed. 5. Contamination from water . The food microbiologist is interested in two aspects of water bacteriology: . 1. Public health aspects . 2. Economic aspects . From the public health point of view the water used about foods should be absolutely safe to drink, i.e., free from pathogens. . From the economic point of view, a water agreeable chemical and bacteriological characteristics is desired for use in connection with the food being handled or processed. The water should have an acceptable taste, odor, color, clarity, chemical composition and bacterial content and should be available in sufficient volume at a desirable temperature. . It also should be uniform in composition. Desirable composition is affected by hardness and alkalinity as well as by the content of organic matter, iron, manganese and fluorine.
5. Contamination from water . The used about foods should meet the bacteriological standards for drinking water and should be acceptable from the sanitary viewpoint as well as the economic viewpoint. . Usually, however, water is more important from the standpoint of the kinds of microorganisms it may introduce into or onto foods than from the standpoint of the total numbers. . Contamination may come from water used as ingredient, for washing foods, for cooling heated foods, and for manufactured ice preserving foods. 6. Contamination from air . Source of microorganisms in air: . Air does not contain a natural flora of microorganisms, for all that are present have come there by accident and usually are on suspended solid materials or in moisture droplets. . Microorganisms get into air on dust or lint; dry soil; spray from streams, lakes or oceans; droplets of moisture from coughing, sneezing, or talking; and growths of sporulating molds on walls, ceilings, floors, foods and ingredients. . Thus the air around a plant manufacturing yeast is high in yeasts, and air of a dairy plant may contain bacteriophages or at least the starter bacteria being used there.
. Kinds of microorganisms in air: . The microorganisms in air have no opportunity for growth but merely persist there, and the kinds that are most resistant to desiccation will live longest. . Mold spores, because their small size, resistance to dry. . It is possible for any kind of bacterium to be suspended in air, especially on dust particles or in moisture droplets. . Cocci usually are more numerous than rod-shaped bacteria, and bacterial spores are relatively uncommon in dust-free air. . Whenever dusts or sprays or various materials are carried up into the air, the microorganisms characteristic of those suspended materials will be present: . Soil organisms from soil and dust, . Water organisms from water spray, . Plant organisms from feed or fodder dust, etc. . Numbers of microorganisms in air . The numbers of microorganisms in air at any given time depend on such factors as the amount of movement, sunshine, humidity, location and the amount of suspended dust or spray. . Numbers of microorganisms in air are increased by air currents caused by movements of people, by ventilation and by breezes. . Direct rays from the sun kill microorganisms suspended in air and hence reduce numbers. . Dry airs usually contains more organisms than does similar air in a moisture condition. . Rain or snow removes organisms from the air, so that a hard, steady rainfall may practically free the air or organisms.
. Various surveys on airborne contamination of foods showed that; 1. The microbial populations of different processing plants are similar, 2. Populations vary tremendously in numbers from one part of a given plant to another, 3. Populations in plant are related to air quality outside the plant, 4. Population levels are related to the level of activity workers. Contamination during handling and processing . The contamination of foods from the natural sources just discussed may take place before the food is harvested or gathered or during handling and processing of the food. . Additional contamination may come from equipment coming in contact with foods, from packaging materials, and from personnel. . The processor attempts to clean and “sanitize” equipment to reduce such contamination and to employ packaging materials that will minimize contamination.
. Kinds of microorganisms on food equipments are depended on: . Kinds of foods being processed, . How being cleaned these equipments, . Storage conditions of these equipments . If vegetables are processed always by same equipments… . If containers are washed with hot or boiling water… . If containers are stored in open air and a dusty environment… . Personnel in food processing plants can contaminate foods during handling and processing. . Various workers suggest that human beings shed from 103 to 104 viable organisms per minute. . The numbers and types of organisms shed are closely related to the subjects’ working environment. . Since the role of the food handler in food-borne disease outbreaks has been clearly demonstrated, from a public health aspect this source of contamination has received considerable attention.
Sources of food-borne pathogens . Staphylococcus aureus? . Salmonella? . Clostridium? . Campylobacter? . Vibrio? . Listeria?