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Food_Safety_Lab - Food Safety LabBacteria as Friends and...

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Food Safety Lab—Bacteria as Friends and Foes A. Laboratory Objectives Students will: Record observations of prepared slides of different bacteria that reside in the GI tract and become familiar with the intestinal microflora through microscopic observation Record observations of slides of bacterial cultures from a yogurt sample Record observations of prepared slides and become familiar with the kinds of microorganisms that cause foodborne illness Observe and record the presence/absence of bacteria on a carrot medium Observe and record the presence/absence of bacterial activity in different samples of milk using methylene blue Laboratory report due: Data Record & Discussion Questions (Sections E & F) B. Introduction Microflora of the Gastrointestinal Tract Bacteria are present all around us, in the soil, in our bodies, on most surfaces in our homes, and in the food we eat. Most of the bacteria in our environment are harmless and some are even beneficial. The intestinal microflora refers to the microorganisms that inhabit the large intestine. Although there are few bacteria in the small intestine, there are several hundred grams of between 300-500 different species of bacteria that reside in the colon. The number of bacterial cells living in the gut is about 10 times greater than the total number of cells in the entire human body. Bacteria that make up the intestinal microflora have a symbiotic relationship with their animal host. The microflora feed upon unabsorbed portions of food such as fiber, some oligosaccharides, and resistant starches in the host diet. The bacteria, in turn, produce nutrients that they can either use themselves or that can be absorbed into the body. These nutrients include small amounts of short chain fatty acids, some B vitamins, and vitamin K, all of which can be beneficial to the host organism. The bacteria can also improve the digestion and absorption of essential nutrients and promote overall colon health. Resident bacteria in the colon have a protective effect against colonization by pathogenic microbes (disease-causing organisms). Prebiotics and Probiotics Dietary fiber is defined as the total polysaccharides and lignin portion of foods that are not digested by human enzymes. Most is plant cell wall material. Humans do not possess the enzymes to break the bonds between the molecules that make up these substances and, as a result, cannot digest them. Although fiber cannot be digested, it plays a vital role in maintenance of gastrointestinal health and even plays a protective role against some types of cancer and cardiovascular disease. Intestinal bacteria digest and metabolize fermentable, soluble dietary fibers. Fibers are examples of prebiotics. Prebiotics are substances that pass undigested into the colon and stimulate the growth and/or activity of certain types of bacteria. A diet that is rich in fruits and vegetables and whole grains contains a wide variety of indigestible carbohydrates that
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