13 - microbial spoilage Flashcards
T or F : milk as high amounts of free amino acids and promotes the growth of microorganisms
false, it has low amounts of FFA
T or F : Milk lipolysis actually happens faster at 4C than at 7C
true because during the cold storage the psychotropic produces more lipases at lower temperautres.
____ is faster at 7˚C while the ___ is faster at 4˚C
7 –> proteolysis
4 –> lipolysis
the ____ bacteria will result in a bitter flavour in milk
psychrotrophic expressing proteases
the ____ bacteria will result in a rancid flavour in milk
psychrotrophic expressing lipase
the ____ (bacteria) will result in a sour flavour in milk
LAB
____ is the more common carbon source for bacterial spoilage of milk
lactose
____ are the main source of nitrogen for bacterial growth in milk
Casein proteins
Why do you usually don’t get spoilage by lipolysis in the fridge
because a few spoilage bacteria can use fat as a carbon source, but only if the globule membrane is physically damaged, otherwise fat is protected by a membrane
Major inhibitors of microbial growth in milk are ____ and _____
lactoperoxidase
lactoferrin
How does lactoferring inhibits the microbes in milk
by binding the iron which is limiting for the growth of microbes in the milk
What is the meachnism of lactoperoxidase to inhibit the microbial growth
the oxidation of thiocyanate (when peroxide is present) to hypocyanate which is an antimicrobial and a oxidant
Why is lactoferin not effective in the case of cow milk
because there is a lot of citrate which binds the lacteroferrin (inhibition of its function to bind iron)
what are the natural inhibitors of the milk
1- lactoferrin 2- lactoperoxidase 3- B12 binding systes 4- lysozyme 5- immunoglobulings 6- folate
Why hydrogen peroxide added to milk?
because it is the limiting substrate of the lactoperoxidase
psychrotrophic bacteria are gram + or gram - ?
gram -
65-70% bacteria isolated from raw milk will be ____
Pseudomonas sp.
____ increase in numbers during milk storage, but eventually they will be over grown by Pseudomadaceae (pseudomonas)
Enterobacteriacea
____ (ogligate/facultative) aerobes will usually be the most populace microbes in spoiled milk
obligate
Psychrotrophic milk spoilage usually relies on ____ to spoil the milk, and to a lesser extent lipolysis
proteolysis
T or F : The bacteria most associated with milk spoilage Pseudomonas sp. are unable to ferment lactose
t
T or F : the bacteria most responsible for the spoilage of milk uses lactose as a source of energy
false, pseudomonas are unable to ferment lactose
Rancid and fruit flavors are the result of ____
lipolysis
Bitter and putrid flavors and coagulation result from ____
proteolysis
