15) Microbial Spoilage and Public Health Concerns (2) Flashcards
why is milk good for growing bacteria?
due to:
- high water content
- near neutral pH
- available nutrients
what does pasteurization do to milk?
pasteurized milk will not support all MOs b/c of low amounts of available AAs
milk spoilage bacteria relies on ___ or ____ for energy generation
proteolysis or lipolysis
compare lipolysis to proteolysis in milk
lipolysis happens faster at 4C b/c psychotropic bacteria have faster growth rate and produces more lipases
proteolysis happens faster at 7C
what is the more common C source for bacterial spoilage of milk? why?
lactose
b/c only select bacteria can degrade lactose
after lactose, what is the secondary source of carbon for microbe growth in milk?
what is the third?
2nd: glucose
3rd: fat (only if the globule membrane is physically damaged)
when is fat used as a C source for spoilage microbe growth in milk?
what is fat protected by when not used as a carbon source?
if the globule membrane is damaged
otherwise, fat is protected by a protective membrane
what is the main source of N for bacterial growth in milk?
casein proteins
what are non-protein N sources in milk?
urea
peptides
AAs
what are major inhibitors of microbial growth in milk?
what are minor inhibitors?
major:
- lactoferrin
- lactoperoxidase
minor
- lysozyme
- immunoglobulins
- folate and vit B12 binding systems
how does lactoferrin act to inhibit microbial growth in milk?
lactoferrin binds iron which makes iron a limiting factor for bacterial growth
how is citrate levels different in cow vs human milk?
what effect does this cause?
human milk: low in citrate
cow’s milk: higher in citrate
citrate binds lactoferrin which decreases lactoferrin’s ability to limit bacterial growth
describe the lactoperoxidase system in cow’s milk
- an effective microbial inhibitor in cow’s milk
- lactoperoxidase survives pasteurization
- lactoperoxidase catalyzes oxidation of thiocyanate (w/ H2O2 presence) which creates hypothiocyanite (an antimicrobial and highly reactive oxidant)
what is hypothiocyanite?
- antimicrobial
- highly reactive oxidant
- the final pdt of the lactoperoxidase system
what is this limiting substrate in the lactoperoxidase system?
H2O2 (hydrogen peroxide)
how can you increase effectiveness of the lactoperoxidase system in milk?
adding H2O2, since it is the limiting substrate
what does the lactoperoxidase system limit?
LABs, coliforms, pathogenic bacteria
how is shelf life of raw-milk extended in developing countries?
add H2O2, which increases effectiveness of lactoperoxidase system, which decreases LABs, coliforms and pathogenic bacteria
preservation of milk relies on ____ and ____
sanitation (pasteurization) and refrigeration
what bacteria spoils raw and pasteurized milk?
psychrotropic bacteria that are aerobic gram-neg rods
in spoiled milk, what is the main MO found?
Pseudomonas sp: 60-75% of bacteria
what MOs will be more commonly found in spoiled refrigerated milk?
obligate aerobes
describe the growth of enterobacteriacea and pseudomadaceae during milk storage
what is an exception to this?
enterobacteriacea increases in numbers but is over grown by pseudomadaceae
except when bacterial spores are present
which process does psychrotropic milk spoilage primarily consist of? what is a secondary process that may occur?
primarily proteolysis
lipolysis may also occur
bacteria most associated w/ milk spoilage Pseudomonas sp. are unable to ______
ferment lactose