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Chapter 10

FOOD 2010 Chapter Notes - Chapter 10: Food Microbiology, Reduction Potential, Protozoa


Department
Food Science
Course Code
FOOD 2010
Professor
Massimo Marcone
Chapter
10

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Chapter 10: Food Microbiology and Fermentation
10.1 What are Microorganisms
-microorganisms are living entities that are too small to be seen with the naked eye
-compromise bacteria, viruses, protozoa, and fungi (yeasts and molds)
-either procaryotes or eucaryotes
-procaryotes = no nucleus in cell - bacteria
-eucaryotes = have nucleus - fungi, protozoa, plants and animals
-viruses are neither cause they are noncellular
-bacteria are unicellular, and are divided into
-gram-positive (thick cell wall and no outer membrane)
-gram-negative (thin cell wall and an outer membrane)
-they are also either
-bacillus (rod)
-spirilium (twisty)
-coccus (small balls)
-some bacteria are able to develop into spores under unfavorable conditions thus
being more able to increase survival in heating, drying and irradiation
-they can then germinate into vegetative cells when conditions improve
-molds are multi or unicellular found in decaying organic matter
-yeasts are unicellular and can grow over a wide range of conditions
-protozoa are single-celled eucaryotes, classified by morphology, locomotion and
life cycle
10.2 Factors Affecting Microbial Growth
-Nutrient Availability
-chemotrophic organisms require chemicals for metabolism
sudivided into
-lithotrophic = require inorganic compounds
-organotrophic = require organic compounds
-phototrophic organisms require energy in the form of light
-nutrient needs depends on organisms and temperature
-may become more exacting in requirement during refrigeration
-water activity
-bacteria need quite a bit of water, minimum aw of 0.90
-yeasts need minimum aw of 0.80
-molds need a minimum aw of 0.70
-this is just a general there are some exceptions
-acidity/alkalinity
-bacteria cannot survive under pH 4.5, optimum 6.5-7.5
-yeasts can live anywhere from pH 3.0-8.5, optimum 4.0-6.5
-molds between pH 2.0-11.0, optimum 4.5-6.8
-the ions will prevent the microorganisms ability to transport molecules in or
out of the cell through the cell membrane
-oxygen
-molds require oxygen (aerobes)
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