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Chapter 10

Chapter 10- Food Microbiology and Fermentation.docx

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Food Science
FOOD 2010
Massimo Marcone

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 a wf 0.90 -yeasts need minimum a ofw0.80 -molds need a minimum a ofw0.70 -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) Chapter 10: Food Microbiology and Fermentation -most bacteria that cause disease prefer aerobic but can grow if not present -temperature -pyschotrophs = prefer higher temperatures but can grow at low ones -thermotrophs = tolerate high temperatures -thermophiles = prefer high temperatures -mesophiles can not tolerate extremes (high or low) -food effects -foods high in protein exert a buffering effect, so microorganisms are able to live and grow even if the pH is below minimum level needed for survival -certain components can change the redox potential (poising effect) -depends on presence of reducing sugars -depends on ability of food tissue to use oxygen (fruit and vegs) -depends on pH of the food -more alkali material = - redox potential therefore more anaerobic -certain microorganisms can adapt to extreme temperatures by synthesizing enzymes or making more unsaturated lipids (both better for cold temps) -using the hurdle concept -nonlethal levels of factors above can be used in combination to inhibit or reduce microorganisms in food -more effective when multiple techniques are combined -more in detail section 8.3 10.3 Foodboorne Microorganisms -sources of microorganisms -can be found pretty much anywhere -can originate from raw food, acquired during handling and processing, survived preservation and storage treatments -types found in food -those that spoil food -those that are pathogenic
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