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
In which cases does the spoilage of milk can occur because of LAB?
- if milk is tempeature abused
- storage at temperatures high enough for the LAB to outgrow the psychrotrophic bacteria
What is the difference between spoiled milk by LAB or fermented milk by LAB
spoiled milk by wild LAB results in the production of off flavors because of propionic acids and other compounds like acetic acid
T or F : Making generalizations about the spoilage of fruits and vegetables is difficult because a single produce item such as a tomato could be cultivated under several different conditions under many different climates
true
Spoilage fungi can form a ____ at the end of their germ tubes
appressorium
What is an appressorium?
Structure used to attach to and then penetrate plant surfaces by mechanical pressure, this can initiate fungal spoilage
To what is due most of the spoilage of fruits and vegetables?
molds and yeasts because of the low pH
T or F : there is no spoilage in the fruits and vegetables unless there is the surface compromised
true
What is the main limitation preventing the growth of bacteria in fruits and vegetables?
the low pH
How are nuts usually preserved?
by lowering the Aw to 0.7
T or F : Most nut spoilage is independent of microbiology and is caused by oxidation of the nut fats
true
____ is a ubiquitous invader, and production of mycotoxin is a major issue
Aspergillus flavus
What is the most important microorganism in the spoilage of peanuts
molds
When does most of the microbial contamination occurs for the cereals?
when they are growing and during the harvest
What is usually done to limit the growth of microbes in cereals?
loweing Aw
___ are the most common contaminants of grains growing in the field and some of these are toxigenic
Molds
What are the two types of fungi that infect grains?
field fungi and storage fungi
What is the Aw that field fungi needs in order to lead to dammage
over 0.9
what are the storage fungi that can result in cereal dammages
aspergillus,
rhizopus
ucro and wallemia
pennecilium
T or F : the mciroorganism that will spoil the bakery products are the same as the ones that will spoil cereals and grains
false
What is the cause of the spoilage of bakd products
molds
Most commercial bakery products contain one or more ___ agents to retard mold growth
fungistatic
What kind of microorganism is responsible or the rope spoilage seen in the bakery products
the bacteria (bacillus subtillis)
