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Food Micro Lecture 3

Food Micro Midterm 1

T or F: Viruses grow abundantly in foods. False
Yeasts require ______ compounds for growth. organic
T or F: Yeasts can grow in anaerobic conditions. False
What is the optimal pH for yeast growth? neutral or slightly acidic
How do yeasts multiply? Budding/spores by sexual mating
What food products are yeast useful for? Alcoholic beverages, baking
Molds require at least _____ moisture for growth. 70%
Describe the mold growth life cycle. Extension of hypha into mycelium, spore formation, spores disperse into air, spores germinate
Bacteria reproduce by ______. binary fission
What factors affect bacterial reproduction? cell type, nutrients available, space, temperature, presence of toxic compounds, age of cell
T or F: Bacteria grow faster than yeasts and molds under optimum conditions. True
What nutrients are necessary for microorganisms to grow? water, source of energy, source of nitrogen, vitamins, minerals
Space limitations usually correlate with _______. nutrient availability
The optimum growth temperature for most foodborne bacteria is ____. 37C
T or F: Bacteria can kill themselves by producing large amounts of toxic compounds. True
T or F: Old cells have a higher surface to volume ratio and thus exhibit slower growth than young cells. False
What are the four microbial growth phases? Lag, log, stationary, death
Describe the lag phase. The first growth phase, the organism is adapting to new surroundings and cell numbers do not increase; they assimilate nutrients and increase in size.
Describe the log or exponential phase. Cells start to increase in numbers, growth is stable and constant; first order kinetics.
Describe the stationary phase. Essential nutrients become depleted or waste products build up so that growth stops; secondary metabolites are produced; population is stable.
Endospore forming bacteria produce endospores during the ______ phase. stationary
Describe the death phase. Viable cell count decreases; cell lysis occurs.
Define generation time. The time period which is takes for bacteria to double.
The bacterial growth curve is ______. logarithmic
Define growth rate. The increase in cell mass per unit time during the exponential growth phase.
The typical growth rate for yeasts and molds is ____. 0.2
The typical growth rate for fast-growing bacteria is ____. 2.5
____ and ____ are the most important factors which affect growth rate. Temperature, time
What are three ways to quantify bacteria? Direct measurement (microscopic count), viable cell count (plate count or colony count), indirect measurement (turbidity)
What are the advantages and disadvantages to direct count? Advantage: actual count, not an estimate Disadvantage: longer, cannot distinguish between living and dead cells
What is the disadvantage to viable cell count? It is not actual cell count, its a measure of CFU.
What is the disadvantage to indirect count? It does not give a quantifiable number.
Describe growth in mixed populations. Growth characteristics will differ depending on optimum conditions of microorganism.
Describe sequence of growth. Different strains will predominate in sequence during storage; growth of one microorganism creates an environment for another and then the first can no longer grow
Describe growth in succession. Includes sequence of growth, but diauxic; one or two types of microorganisms can grow optimally, then create an environment which they can no longer grow in but allow for growth of another organism
Describe symbiotic growth. One type of cell produces metabolic products that another needs for growth and vice versa.
Describe synergistic growth. Observed during symbiotic growth of more than two organisms.
Describe antagonistic growth. The growth of one bacteria inhibits the growth of another.
Created by: goberoi
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