Food microbiology exam test quiz
and answers graded A+
water (intrinsic factor) - ANS✅✅fresh meats and veggies provide ample water
if water = life then by limiting the availability of water then life is stopped and microbial growth is
stopped
-sun-dried tomatoes, dried mushrooms, jerky, dried herbs
highly salted or sugary foods provide little water for microorganisms even when they appear moist
(salt/sugar will suck water out of any cell/spore that's present)
-salted eggs
-jams or jelly
fungi can grow with less available water than bacteria
-old bread, cheese, jam often become moldy but rarely spoil due to bacterias (slide5)
pH (intrinsic factor) - ANS✅✅many bacterias and most pathogens are inhibiting by acidic
conditions below pH 4.5
-ONE exception to this is the lactic acid bacteria which can grow at a pH of 3.5
(these usually produce lactic acid during fermentation and are used in yogurt and sauerkraut)
canning requirements for acidic food is more stringent than less acidic foods
fungi can grow in a more acidic environment than most bacterias (as well as more dry and cold)
nutrients (intrinsic factor) - ANS✅✅an organism that requires a specific vitamin or nutrient cannot
grow in a food lacking that particular vitamin or nutrient
Pseudomonas spoil often because they can grow and synthesize essential nutrients in various
environments including refrigerators
, biological barriers (intrinsic factor) - ANS✅✅rinds, shells, or other covering may delay invasion by
microorganisms
ex: whole lemons last longer than sliced lemons
ex: eggs with complete shell last longer than egg with cracks
(also slide 11)
antimicrobial chemicals (intrinsic factors) - ANS✅✅egg whites : rich in lysozyme (attacks
peptidoglycan aka tears, mucous membranes, etc)
cranberries: have benzoic acid
garlic : has allicin which is antibacterial and anti-fungal
(called Russian penicillin during world war 2)
raw milk: contains peroxidase enzymes similar to those in WBCs and saliva which turn hydrogen
peroxide into ROS
(pasteurization kills these enzymes unfortunately)
low temperature (extrinsic factor) - ANS✅✅a temperature below freezing makes water
unavailable
-at lower temperatures that are above freezing, many enzymatic reactions are halted or dramatically
slowed
-most food spoilage microorganisms are mesophiles (room temp)
ex: Pseudomonas will spoil food more slowly in fridge than at room temp , this extends shelf life of
many things
higher temperature ( extrinsic factor) - ANS✅✅at higher temperatures many enzymatic reactions
are inhibited for most enzymes as well
-most food spoilage microorganisms are mesophiles
and answers graded A+
water (intrinsic factor) - ANS✅✅fresh meats and veggies provide ample water
if water = life then by limiting the availability of water then life is stopped and microbial growth is
stopped
-sun-dried tomatoes, dried mushrooms, jerky, dried herbs
highly salted or sugary foods provide little water for microorganisms even when they appear moist
(salt/sugar will suck water out of any cell/spore that's present)
-salted eggs
-jams or jelly
fungi can grow with less available water than bacteria
-old bread, cheese, jam often become moldy but rarely spoil due to bacterias (slide5)
pH (intrinsic factor) - ANS✅✅many bacterias and most pathogens are inhibiting by acidic
conditions below pH 4.5
-ONE exception to this is the lactic acid bacteria which can grow at a pH of 3.5
(these usually produce lactic acid during fermentation and are used in yogurt and sauerkraut)
canning requirements for acidic food is more stringent than less acidic foods
fungi can grow in a more acidic environment than most bacterias (as well as more dry and cold)
nutrients (intrinsic factor) - ANS✅✅an organism that requires a specific vitamin or nutrient cannot
grow in a food lacking that particular vitamin or nutrient
Pseudomonas spoil often because they can grow and synthesize essential nutrients in various
environments including refrigerators
, biological barriers (intrinsic factor) - ANS✅✅rinds, shells, or other covering may delay invasion by
microorganisms
ex: whole lemons last longer than sliced lemons
ex: eggs with complete shell last longer than egg with cracks
(also slide 11)
antimicrobial chemicals (intrinsic factors) - ANS✅✅egg whites : rich in lysozyme (attacks
peptidoglycan aka tears, mucous membranes, etc)
cranberries: have benzoic acid
garlic : has allicin which is antibacterial and anti-fungal
(called Russian penicillin during world war 2)
raw milk: contains peroxidase enzymes similar to those in WBCs and saliva which turn hydrogen
peroxide into ROS
(pasteurization kills these enzymes unfortunately)
low temperature (extrinsic factor) - ANS✅✅a temperature below freezing makes water
unavailable
-at lower temperatures that are above freezing, many enzymatic reactions are halted or dramatically
slowed
-most food spoilage microorganisms are mesophiles (room temp)
ex: Pseudomonas will spoil food more slowly in fridge than at room temp , this extends shelf life of
many things
higher temperature ( extrinsic factor) - ANS✅✅at higher temperatures many enzymatic reactions
are inhibited for most enzymes as well
-most food spoilage microorganisms are mesophiles
