MICROBES are microorganisms that are ever present

Transcription

1 Microbes in Food Science MICROBES are microorganisms that are ever present in the world around us. Whenever a plant or animal dies, microbes begin to break down the once-living organism into usable energy for themselves. In the process, the organism decays and degrades. This is what happens in food spoilage. However, some microbes are beneficial in food science. Objective: Describe the different microbes that affect food quality and spoilage. Key Terms: aerobic anaerobic asexual reproduction binary fission budding food microbiology heterotrophic mesophiles molds psychrophiles thermophiles E-unit: Microbes in Food Science Page 1 AgEdLibrary.com

2 Microbes That Affect Food Food producers and consumers are constantly fighting the battle of food spoilage. The race from producer to consumer, which was a sprint decades ago, has now become more of a marathon. Microbes are still present to begin the spoiling process, but because of the use of new technology and age-old techniques, food is safer and stays fresh longer for consumers to enjoy. There are three main microbes that are the focus of food microbiology, the study of microorganisms and their effect on the food industry. Molds, yeast, and bacteria are the main causes of most food spoilage, yet some of these microbes actually benefit food production and are used to create some of our favorite foods. MOLDS If you have ever left a loaf of bread on the counter for too long, you may have noticed a fuzzy growth beginning to spread across the surface of the bread. Molds are part of the fungus family and feed on decaying organisms for energy. Fungi are adaptable enough to live nearly anywhere, provided they have air and moisture. Inside the bread bag, on a warm countertop, surrounded by moist bread, is a perfect place for mold to begin growing. FIGURE 1. Microbes are an ever-present threat to the food industry. (Courtesy, Agricultural Research Service, USDA) FIGURE 2. Molds will grow wherever conditions are favorable. (Courtesy, Agricultural Research Service, USDA) Molds, like other fungi, reproduce asexually. Asexual reproduction is the forming of offspring by simple cell division (mitosis) rather than by the union of sperm and egg. Male and female organisms are not needed for asexual reproduction because the offspring grows and splits directly from the parent. Molds have the ability to produce spores, which are released into the air and carried to new locations. Mold spores fill our air supply but will only grow into mold colonies when the spores land where conditions are favorable. When we open a bag of E-unit: Microbes in Food Science Page 2 AgEdLibrary.com

3 bread, the air that enters the bag will carry enough mold spores to cause the fungus to spread if given enough time. Molds grow by the formation of filaments that extend above or below the food surface, giving the colonies a fuzzy appearance. In the process of consuming the food source for energy, molds can produce byproducts known as mycotoxins. Mycotoxins, such as aflatoxin in corn, can be deadly to humans or animals that consume the contaminated food. Some forms of molds can actually be beneficial to food producers. Many types of cheese rely on the action of molds to provide the colors and flavors that consumers want. Medicines, such as penicillin and other antibiotics, are also produced through the action of molds. Molds are unique in the way they are able to thrive in extremely high temperatures as well as very low temperatures. Molds can be grouped into three categories based on their ability to withstand temperature extremes. Mesophiles are those molds that grow best at room temperature (between 50 and 110 F, 10 and 43.3 C). These molds are the type most commonly found invading food products that are not refrigerated and usually left on countertops or stored in pantries. Psychrophiles are a group of molds that grow best at temperatures of less than 50 F (10 C). These molds can be present in a refrigerator and can be noticed on older foods and sometimes around the door seal, which is seldom cleaned regularly. The final group, thermophiles, consists of molds that thrive at high temperatures, between 110 and 140 F (43.3 and 60 C). These molds are less common in our homes and kitchens because of the lack of a constant high temperature. They could develop inside a sealed, clear container (think of the bread bag) that is being exposed to sunlight on a countertop. The container could act as sort of a mini-greenhouse, trapping heat and raising the temperature inside. Although molds may need different temperature ranges in which to thrive, one thing all molds need to survive is oxygen. Molds require an environment that is aerobic, or has oxygen present. One of the best ways to control mold growth is to remove the source of oxygen, producing an anaerobic environment. Food packagers are constantly researching ways to remove oxygen from inside food packages and keep it out for the duration of the food storage. Even our tightest-sealing containers at home still allow oxygen to enter when they are opened and then sealed again. Only vacuum-sealed food is able to withstand long periods without the threat of mold growth. FIGURE 3. Sealed jars of vegetables have no oxygen present inside the containers, thus halting the growth of any molds without the need for refrigeration. E-unit: Microbes in Food Science Page 3 AgEdLibrary.com

4 YEAST Another microbe that is both friend and foe to the food industry is yeast. Yeasts are unicellular (single-celled) organisms that are actually part of the fungi family. Yeasts survive by converting sugars and starches to usable energy. Reproduction for yeasts comes in the form of budding. Budding is a process of asexual reproduction in which a small knob forms on the parent organism. This bud will grow and eventually split away from the parent, creating a new organism identical to the parent. If asked for the main contribution of yeast, most of us would think of bread making. In that process, yeast converts the sugars and starches present in the bread dough into carbon dioxide and water. The carbon dioxide released is trapped in small bubbles in the sticky dough. This causes the mixture to rise, Without yeast in our bread, we would have very flat, hard loaves after baking. Yeasts are also commonly used in processes that require fermentation. Yeasts are added to a variety of food products, including wines, beers, and soy sauce to begin the fermentation process. As the sugars in grapes (in the case of wine) are consumed, alcohol is produced as a byproduct. The longer the mixture is allowed to ferment, the stronger the alcohol content of the final liquid will be. Not all contributions of yeasts are beneficial, though. Yeasts are also responsible for food spoilage and sickness in some cases. Yeasts can survive in either aerobic or anaerobic environments, in high or low ph conditions, and at a variety of temperatures. These qualities make yeasts tough competitors when it comes to the fight against food spoilage. FIGURE 4. Yeasts are both friends and foes when it comes to food preservation. (Courtesy, Agricultural Research Service, USDA) BACTERIA If molds and yeasts were soldiers for food spoilage, bacteria would be commandos. Bacteria are the most difficult of all microbes to control when it comes to food spoilage because of their ability to adapt to nearly any condition on Earth. Bacteria can and will be found everywhere on the planet. These microorganisms can live with or without oxygen, survive at any temperature extreme, and use anything as a food source. Bacteria have even been found on hot-water vents deep in the ocean where no other organisms can survive. E-unit: Microbes in Food Science Page 4 AgEdLibrary.com

5 Bacteria come in a variety of shapes, but they are all single-celled organisms. Some bacteria may be able to create their own food source, much like plants. However, the bacteria commonly responsible for food spoilage are heterotrophic; that is, they require the intake of food and nutrients to survive. Bacteria reproduce by a process of binary fission, in which the DNA in the bacterial cell is replicated and the cell splits into two identical cells. Under the correct conditions, some bacteria are able to reproduce every 20 minutes. With that schedule, a single bacterial cell could produce 17 million offspring in only eight hours! Think of that the next time you reach for leftovers that have been sitting out all afternoon at a family picnic. Because of their high reproductive rates, ability to adapt, and variety of food sources, bacteria are the most difficult (and most dangerous) of all microbes associated with food spoilage. Proper cooking and refrigeration can slow the growth of bacteria but not stop them completely. FIGURE 5. Bacteria can be found anywhere and everywhere on Earth. (Courtesy, Agricultural Research Service, USDA) Summary: Microbes are ever present in our environment. Molds, yeast, and bacteria are the main causes of most food spoilage, yet some of these microbes actually benefit food production and are used to create some of our favorite foods. Scientists, food processors, and food packagers are all working to use the best possible methods for controlling and inhibiting undesirable microbial growth in our food. Checking Your Knowledge: 1. List and briefly define the three common microbes that cause food spoilage. 2. What is the process of budding in yeast cells? 3. List the three types of molds and give the optimal temperature for each group. E-unit: Microbes in Food Science Page 5 AgEdLibrary.com

6 Expanding Your Knowledge: Expose a variety of food items to different environmental conditions and observe the growth of mold or the deterioration of the products. Conclude which environmental conditions favor the growth of microbes. Web Links: National Restaurant Association Reducing Food Spoilage FoodService.com Food Spoilage Agricultural Career Profiles E-unit: Microbes in Food Science Page 6 AgEdLibrary.com