Exam 3 Study Guide - Food Science Microbiology Exam Study...

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1 Food Science Microbiology Exam Study Guide ____________________________________________________________________________________________________________ BASIC CONCEPTS MICROBIAL NEEDS (FATTOM) Food microbes have varying needs in food/nutrients required for growth Bacteria especially partial to high protein foods and known as “potentially hazardous” *Milk, meat, poultry, fish provide moist + favorable environment] Nitrogen from amino acids, carbon for energy, minerals and vitamins Yeast prefer simple sugars Molds prefer complex carbohydrates Acidity pH most bacteria we are concerned with grow on human body that grow best in pH that is neutral/biological 6.8~7.4. Extreme shifts in pH can damage cells. Most foods are slightly acidic. Acidic Foods with pH lower than 4.6 such as limes, grapefruit, pickles, tomatoes, pineapple are not considered favorable environments for microbial growth Fungi (Yeasts + Molds) prefer slightly acidic conditions grow best between pH 5~6 (normal human skin) Lactobacilli (acidophile) establish low pH of 3~4 not favorable for pathogens Low Acid Foods foods with pH 4.6~7 such as lettuce, celery, milk, meat, fish, egg white, corn. Corn needs more heat since as the pH increases the foods become more heat resistant. Temperature variety of temperatures but most have favorable between 60~110F. “Danger Zone” of microbial growth 40~140 °F. Most die after 140 °F, but not spores that can survive boiling. Psychrophile 32~45 °F can also grow as low as 19 °F if freeze they grow slower, but bacteria are not killed Mesophile 60~110 °F Thermophile 110- 130 °F they “love” “heat” and found in hot springs and compost heaps Oxygen varying among whether bacteria can grow with the presence of free oxygen or when O 2 is excluded. Most are adaptable/facultative. Aerobes only can grow when supplied with free oxygen [ Pseudomonas aeruginosa ] Anaerobes oxygen is toxic to these organisms, can only grow in vacuum [ Clostridium ] Facultative - adaptable can use oxygen when present but can switch to anaerobic pathways in its absence [ Escherichia coli ] Moisture Content quantity of water contained in a material Water Activity measure of how efficiently water present can take part in a chemical/physical reaction A w > 0.9 Bacteria + Yeast Milk 0.98~0.99 A w < 0.9 Molds can tolerate lower water activity Dried Fruits 0.60~0.75 Jams, Honey 0.80 Maple Syrup 0.90 ____________________________________________________________________________________________________________ MICROBIAL GROUPS Molds fungi, made of tubular elements called hyphae, grow quickly look like tangled, fuzzy mass can be visible to the naked eye. Some mold produce toxins that lead to foodborne illness known as mycotoxicoses, others are useful for penicillin and ripening cheeses. Mostly spoil foods, great adaptability
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This note was uploaded on 03/02/2010 for the course FOOD-SCI 150 taught by Professor Levin during the Spring '09 term at UMass (Amherst).

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Exam 3 Study Guide - Food Science Microbiology Exam Study...

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