Food microbiology Flashcards
what factors influence microbial growth
environmental factors (that humans can control) and nutritional requirements
how is thermotolerance related to microbial growth
at freezing temperatures water crystalizes - inaccessible which stops microbial growth, in fridge microbes can multiply slowly or not at all, cooking food can also destroy bacteria
what are some microbes that can survive fridge temperatures
Listeria and Pseudomonas (mesophiles or psychrophiles)
what is a bacterium that is a mesophile but can contaminate food after cooking, how?
clostridium botulinum can using spores because once the food cools it can germinate and cause illness
how do some thermotolerant organisms survive heat
some can simply survive, some release heat resistant toxins
how do atmospherical conditions limit bacterial growth / what is the exception / how do you mitigate this exception
removal of oxygen limits many organisms / except anaerobes / use heat in conjunction with oxygen removal
how does salt influence microbial growth / what can solutes be
it puts cells in hypertonic solutions which cause them to dehydrate (water rushes out) / can be salt or sugar
what kind of organisms are resistant to osmotic stress
halotolerant organisms are able to replicate in high salt or high sugar
where do most foodborne bacteria lie on the water activity scale / what happens as the water activity decreases in a food
0.90-1 (mostly water) so things like fresh meat / as the food gets closer to 0 it gets harder for microbes to grow because they are super dry
what organisms can survive dry environments
halotolerant and dessication resistant organisms
what fungus was linked to the witch trials and why
ergotamine because it grows on wet & improperly stored rye - got into the bread and is a psychedelic similar to LSD - made people think there was witches around
why are acidic foods made shelf stable without the need for extreme heat / how do higher pH food need to be processed
acids limit microbial growth / need to have high pressure and high heat to raise the boiling temperature of the water
what is fermentation / what is its purpose
the controlled growth of specific microbes within a food / to preserve food (limit microbial growth), to improve digestibility (break down fibers), add nutrients (vitamins we cannot make)
what are the three major classes of fermentation reactions
bacteria, fungus, and fungus + bacteria
what is lactic acid bacteria / what does their fermentation primarily produce
a gram positive, aerotolerant anaerobe (can survive in O2), obligate fermenters, highly halotolerant, acidophiles / lactic acid
