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FDSC442 > 13 - microbial spoilage > Flashcards

13 - microbial spoilage Flashcards

1
Q

T or F : milk as high amounts of free amino acids and promotes the growth of microorganisms

A

false, it has low amounts of FFA

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2
Q

T or F : Milk lipolysis actually happens faster at 4C than at 7C

A

true because during the cold storage the psychotropic produces more lipases at lower temperautres.

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3
Q

____ is faster at 7˚C while the ___ is faster at 4˚C

A

7 –> proteolysis

4 –> lipolysis

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4
Q

the ____ bacteria will result in a bitter flavour in milk

A

psychrotrophic expressing proteases

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5
Q

the ____ bacteria will result in a rancid flavour in milk

A

psychrotrophic expressing lipase

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6
Q

the ____ (bacteria) will result in a sour flavour in milk

A

LAB

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7
Q

____ is the more common carbon source for bacterial spoilage of milk

A

lactose

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8
Q

____ are the main source of nitrogen for bacterial growth in milk

A

Casein proteins

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9
Q

Why do you usually don’t get spoilage by lipolysis in the fridge

A

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

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10
Q

Major inhibitors of microbial growth in milk are ____ and _____

A

lactoperoxidase

lactoferrin

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11
Q

How does lactoferring inhibits the microbes in milk

A

by binding the iron which is limiting for the growth of microbes in the milk

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12
Q

What is the meachnism of lactoperoxidase to inhibit the microbial growth

A

the oxidation of thiocyanate (when peroxide is present) to hypocyanate which is an antimicrobial and a oxidant

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13
Q

Why is lactoferin not effective in the case of cow milk

A

because there is a lot of citrate which binds the lacteroferrin (inhibition of its function to bind iron)

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14
Q

what are the natural inhibitors of the milk

A 
1- lactoferrin 
2- lactoperoxidase
3- B12 binding systes
4- lysozyme
5- immunoglobulings
6- folate
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15
Q

Why hydrogen peroxide added to milk?

A

because it is the limiting substrate of the lactoperoxidase

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16
Q

psychrotrophic bacteria are gram + or gram - ?

A

gram -

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17
Q

65-70% bacteria isolated from raw milk will be ____

A

Pseudomonas sp.

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18
Q

____ increase in numbers during milk storage, but eventually they will be over grown by Pseudomadaceae (pseudomonas)

A

Enterobacteriacea

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19
Q

____ (ogligate/facultative) aerobes will usually be the most populace microbes in spoiled milk

A

obligate

20
Q

Psychrotrophic milk spoilage usually relies on ____ to spoil the milk, and to a lesser extent lipolysis

A

proteolysis

21
Q

T or F : The bacteria most associated with milk spoilage Pseudomonas sp. are unable to ferment lactose

A

t

22
Q

T or F : the bacteria most responsible for the spoilage of milk uses lactose as a source of energy

A

false, pseudomonas are unable to ferment lactose

23
Q

Rancid and fruit flavors are the result of ____

A

lipolysis

24
Q

Bitter and putrid flavors and coagulation result from ____

A

proteolysis

25
Q

In which cases does the spoilage of milk can occur because of LAB?

A
  • if milk is tempeature abused

- storage at temperatures high enough for the LAB to outgrow the psychrotrophic bacteria

26
Q

What is the difference between spoiled milk by LAB or fermented milk by LAB

A

spoiled milk by wild LAB results in the production of off flavors because of propionic acids and other compounds like acetic acid

27
Q

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

A

true

28
Q

Spoilage fungi can form a ____ at the end of their germ tubes

A

appressorium

29
Q

What is an appressorium?

A

Structure used to attach to and then penetrate plant surfaces by mechanical pressure, this can initiate fungal spoilage

30
Q

To what is due most of the spoilage of fruits and vegetables?

A

molds and yeasts because of the low pH

31
Q

T or F : there is no spoilage in the fruits and vegetables unless there is the surface compromised

A

true

32
Q

What is the main limitation preventing the growth of bacteria in fruits and vegetables?

A

the low pH

33
Q

How are nuts usually preserved?

A

by lowering the Aw to 0.7

34
Q

T or F : Most nut spoilage is independent of microbiology and is caused by oxidation of the nut fats

A

true

35
Q

____ is a ubiquitous invader, and production of mycotoxin is a major issue

A

Aspergillus flavus

36
Q

What is the most important microorganism in the spoilage of peanuts

A

molds

37
Q

When does most of the microbial contamination occurs for the cereals?

A

when they are growing and during the harvest

38
Q

What is usually done to limit the growth of microbes in cereals?

A

loweing Aw

39
Q

___ are the most common contaminants of grains growing in the field and some of these are toxigenic

A

Molds

40
Q

What are the two types of fungi that infect grains?

A

field fungi and storage fungi

41
Q

What is the Aw that field fungi needs in order to lead to dammage

A

over 0.9

42
Q

what are the storage fungi that can result in cereal dammages

A

aspergillus,
rhizopus
ucro and wallemia
pennecilium

43
Q

T or F : the mciroorganism that will spoil the bakery products are the same as the ones that will spoil cereals and grains

A

false

44
Q

What is the cause of the spoilage of bakd products

A

molds

45
Q

Most commercial bakery products contain one or more ___ agents to retard mold growth

A

fungistatic

46
Q

What kind of microorganism is responsible or the rope spoilage seen in the bakery products

A

the bacteria (bacillus subtillis)

FDSC442 (19 decks)

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