Introduction to the Microbiology of Food. The Microorganisms. The tiniest life forms are bacteria, yeasts, molds, and viruses, termed “microorganisms” because of their size (micro meaning small and organism meaning living being). Bacteria. 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. Latest environmental news, features and updates. Pictures, video and more. 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 1. 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 1. If there are 1. 00. Some rod- shaped bacteria are capable of existing in two forms, dormant spores and active vegetative cells. Vegetative cells form spores under adverse conditions as a means of survival. Spore forms preserve the bacteria from starvation, drying, freezing, chemicals, and heat. When conditions become favorable, the spores germinate, with each spore again becoming a vegetative cell with the ability to reproduce. Among the bacteria, sporulation is not a means of reproduction since each cell forms a single spore which later germinates into a single cell again. Most sporulating bacteria that grow in the presence of air belong to the Genus Bacillus, and most that grow only in the absence of air belong to the Genus Clostridium. Yeasts and Molds. Yeasts are oval- shaped and slightly larger than bacteria. They reproduce most often by budding. In budding each cell can produce several buds, or swellings, which break away to form new, fully formed daughter cells. All across the world, people are facing a wealth of new and challenging environmental problems everyday. Here are 15 major current environmental problems that our. Animal extinction of most recent times is mainly the result of expanding human demand for animal and other natural resources. Explore these and other causes in depth. An easy-to-understand introduction to environmentalism. What problems does our planet face and what are the solutions? Kermit was wrong. It's so easy being green. Let me show you how with simple, affordable, baby steps. Allegheny Riverfront Green Boulevard Study Urban Redevelopment Authority of Pittsburgh Pittsburgh, Pennsylvania, United States As part of a team led by Sasaki. Information about preventing and managing nuisance wildlife species. Acquired trait: A phenotypic characteristic, acquired during growth and development, that is not genetically based and therefore cannot be passed on to the next. Terrestrial habitat types include forests, grasslands, wetlands and deserts. Within these broad biomes are more specific habitats with varying climate types. Molds as found on bread, fruit, damp paper, or other surfaces are actually composed of millions of microscopic cells joined together to form chains. The chains usually have numerous branches, called hyphae. Molds can thrive in conditions too adverse for bacteria or yeasts. They reproduce by spores that are frequently present as green or black masses on the protruding hyphae. Yeasts and molds grow on most foods, on equipment, and building surfaces where there are small amounts of nutrient and moisture. Since bacteria grow faster, they greatly outnumber yeasts and molds in most foods. However, bacteria find conditions of low p. H, moisture, or temperature and high salt or sugar unfavorable. In such environments, yeasts or molds predominate. Thus, they can be a problem in dry foods, salted fish, bread, pickles, fruits, jams, jellies, and similar commodities. Viruses. Viruses are the smallest and simplest microorganisms. Unlike bacteria, yeasts, and molds, viruses are incapable of reproducing independently. Instead, they must first invade the cells of another living organism called the host, before they can multiply. Hence, they are parasitic. Viruses are normally specific in their selection of host cells, some infecting but one species, while others are capable of infecting closely related species. As a result, viruses which infect bacteria, called bacteriophages, cannot infect human beings or other animals. On the other hand, several animal viruses, known as zoonotis, can infect human beings. The viruses are important to the food process in two respects: As a bacteriophage of lactic or other fermentative bacteria. Bacteriophage infections of starter cultures can interfere seriously with the manufacture of cheese, buttermilk, sauerkraut, pickles, wine, beer, and other desirable fermentative products. As disease transmitted by food to human beings. Although viruses require a live host cell and cannot multiply in foods, they can remain viable and infectious for long periods of time, even under highly adverse conditions, such as drying, freezing, and pasteurization. Factors Affecting Growth of Microorganisms. The food processor reduces potential problems from microorganisms in several ways: Removing or destroying them by trimming, washing, heating, pickling, by adding chemicals, or by encouraging competition by acid- or alcohol- forming organisms. Minimizing contamination from equipment, people, the environment, and from unprocessed food. Minimizing microbial growth on equipment, by cleaning and sanitizing, and in the product itself by adjusting storage temperature, p. H, and other environmental factors. Although each factor affecting growth is considered separately in the following discussion, these factors occur simultaneously in nature. When more than one condition is somewhat adverse to microbial growth, their inhibitory effects are cumulative. Temperature. Temperature is the most efficient means to control microbial growth. Based on their tolerance of broad temperature ranges, microorganisms are roughly classified as follows: Psychrophies grow only at refrigeration temperatures. Psychrotrophs grow well at refrigeration temperatures, but better at room temperature. Mesophiles grow best at or near human body temperature, but grow well at room temperature. Thermophiles grow only at temperatures about as hot as the human hand can endure, and usually not at all at or below body temperature. To be more specific about these temperature limits of growth is to enter the controversy that has continued since the infancy of microbiology, for there are many species that grow in temperature ranges overlapping these. However, for food microbiology these conclusions are pertinent: Figure 1. Low temperature limits growth of food poisoning and food spoilage organisms. There are a few reports of growth, usually of molds, at 1. This means that the standard storage temperature for frozen foods, O. However, many microorganisms survive freezing (Michener and Elliott, 1. Most psychrotrophs have difficulty growing above 9. The food processor can feel safe in the knowledge that foods held above or below the limits in Figure 1 and rotated properly will remain safe. A good rule of thumb is to store perishable foods below 4. Growth of bacteria on chicken at three temperatures. Effect of temperature on time for chicken meat to spoil.(From data of Lochhead and Landerkin, 1. Barnes and Shrimpton, 1. Within the growth range, the rate of growth increases rapidly as the temperature is raised (Figure 2). Conversely, microbial growth rates decrease rapidly as the temperature is lowered and, hence, food spoilage occurs much more slowly. This effect is especially marked near the freezing point. Note in Figure 3 that a drop from about 4. It is only roughly related to percent moisture. Pure water has an aw of 1. ERH) of 1. 00%. If we add an ounce of rocks to a quart of water in such a container, the ERH and the aw will not change. But if we add an ounce of salt, the ERH will fall to about 9. Rocks do not dissolve in water but salt does, thereby reducing the proportion of water that can enter the atmosphere. Likewise, the amount of water available to microorganisms present in the solution is reduced. Yet the percent moisture is the same in the container with rocks as it is in the container with, salt, namely, 9. The GMP regulations for low- acid canned foods defined water activity as the vapor pressure of the food product divided by the vapor pressure of pure water under identical conditions of pressure and temperature. The regulations define low- acid foods as foods, other than beverages, with a finished equilibrium p. H value greater than 4. Table 1. The water activity (aw) limits for growth of principal foodborne disease organisms.*Microorganism. Minimal aw for growth. Reference. Salmonella. Christian & Scott, 1. Clostridium botulinum. Scott, 1. 95. 7Clostridium perfringens. Kang, et al., 1. 96. Staphylococcus aureus. Scott, 1. 96. 2Vibrio parahaemolyticus. Beuchat, 1. 97. 4*These limits are the lowest reported, with all other growth conditions optimal. If other conditions are less than optimal, the minimal aw will be higher.**Troller and Stinson (1. Most bacteria fail to grow in a food or other medium where the aw is lower than 0. Bacteria require a higher aw than yeasts, which in turn require a higher aw than molds. Thus, any condition that lowers the aw first inhibits bacteria, then yeasts, and finally molds (Elliott and Michener, 1. But each species has its limits which are interrelated with other growth factors. Table 2 gives the aw limits for growth of principal foodborne disease organisms held under otherwise optimal conditions. Certain molds and bacteria can grow on fish immersed in saturated salt solution where the aw is about 0. Some molds can grow in foods with aw 0. Elliott and Michener, 1. At these lower limits, growth is very slow. The aw of fully dried foods, such as crackers or sugar, is about 0. The stability of intermediate moisture foods (aw 0. H, pasteurization, chemical additives, and impervious packaging. Hp. H is a term used to describe the acidity or alkalinity of a solution. At p. H 7, there is an equal amount of acid (hydrogen ion: H +) and alkali (hydroxyl ion: OH- ), so the solution is “neutral”. For example, at p. H 5 there are 1. 0 times as many H + as at p. H 6; at p. H 3 there are 1. H + as at p. H 5, and so on. H has a profound effect on the growth of microorganisms. Most bacteria grow best at about p. H 7 and grow poorly or not at all below p. H 4. Yeasts and molds, therefore, predominate in low p. H foods where bacteria cannot compete. The lactic acid bacteria are exceptions; they can grow in high acid foods and actually produce acid to give us sour milk, pickles, fermented meats, and similar products. Some strains, called Leuconostoc contribute off- flavors to orange juice. The p. H values of certain foods are given in Table 2. Table 2. Mean p. H Values of Selected Foods (Lopez, 1. H Value. Selected Foods. Lemon juice (2. 3), Cranberry sauce (2. Rhubarb (3. 1)Applesauce (3. Cherries, RSP (3. Berries (3. 0 – 3. Sauerkraut (3. 5)Peaches (3. Orange juice (3. 7)Apricots (3. Cabbage, red (4. 2), Pears (4. Tomatoes (4. 3)4. How Do Humans Cause Global Warming? Congratulate yourself for wanting to learn more about the main cause of global warming. Not only does our species create huge problems that are beyond the ability of other animals to create, but we have the fortunate ability to analyze them and work to bring an end to their consequences. You are now actively engaged in that process! Humans cause global warming with our unique ability to capture and use energy from stored energy sources. No other animal can start fires or build gasoline engines. Consider your home and the environment in which it is situated. The very fact that you live in one place, something that was quite uncommon before the discovery of stored energy sources like fossil fuels, speaks to how your life is facilitated by these unique energy sources. Even your basic needs are dependent on fossil fuels. Your water, food, and fuel for heating and cooking likely travel hundreds if not thousands of miles to your home. This pattern couldn’t be sustained if humans didn’t have the ability to exploit dense energy sources such as coal, oil, and natural gas. However, their discovery transformed the face of the earth and the nature of humans. The effects on earth are dangerous. In the last 1. 50 years, the human population has grown by more than five times and the average person uses more energy than ever. This energy comes largely from fossil fuels, the use of which is a direct and important cause of global warming. Global Warming is a Growing Problem. The growth of the human population and the growth of consumption adds up to an ever- escalating carbon output. You’ve probably heard a lot of talk about global warming, but if we want to decrease global warming, then the amount of carbon released each year by humans must be drastically reduced. Human Consumption or Human Population? Two factors are acting as catalysts of increased carbon levels in our atmosphere: Increasing consumption among the wealthy (that means you!)Increasing population among the poor. You may wonder which is the primary culprit. The answer is clear – both! Consider the following: Americans consume 3. From this it becomes clear why humans are the main cause of global warming. However, it is even more important for you to understand that you have the power to help prevent global warming from getting worse — live The Green Life. Related Stories: 1. Years of Fossil Fuels in 3. Seconds . Humans Cause Global Warming: 1. Indicators. 3. 1. One- Liners to Respond to Climate Science Myths. Going Green Tips. Image Credit: AZRainman.
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