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Micro > Microbial Detection In Foods > Flashcards

Microbial Detection In Foods Flashcards

1
Q

Reasons to detect microorganism in food

A

Food quality
Food safety
Legal requirement

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2
Q

Challenges in microbiological analysis of foods

A 
Complex matrix 
Other microorganisms 
Cells attachment 
Inhibitory effects of food
Method limitations 
Physiological state of microorganisms 
Non uniform distribution
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3
Q

Types of microbiological methods

A 
Culture 
Microscopic
Chemical 
Physical
Biochemical 
Molecular 
Immunological
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4
Q

Detection methods

A

Conventional

Novel

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5
Q

Conventional method include

A

Culture method
Direct and indirect enumeration
Bacterial toxins
ELISA

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6
Q

Novel methods include

A

Immunogenetic separation
PCR and hybridization
Biosensor
Bacteriophage

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7
Q

Microbiological analysis steps

A

Sampling
Amplification
Detection
Confirmation

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8
Q

What is the principles of culture methods ?

A

Ability of microorganisms to grow in specific media

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9
Q

Limitations of culture methods

A

Time consuming
Cell injury- inability to grow on selective media after surviving a sub lethal stress
Viable but non culturable state - live cells that lost the ability to grow in culture media

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10
Q

Basic steps for ELISA

A

Antigen of interest absorbed on plastic surface
Antigen is recognized by specific antibody
Antibody is recognized by second ab which has enzyme attached
Substrate reacts with enzymes to produce product -colored

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11
Q

What does ELISA plate reader measure?

A

It measures color density in plate well

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12
Q

What is PCR?

A

PCR is a technique that takes a specific sequence of DNA of small amounts and amplifies it to be used for detection and further testing

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13
Q

PCR target ?

A

Sequence of DNA on each end of the region of interest which can be a complete gene or a small sequence

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14
Q

What are primers

A

Primers are 15-30 nucleotides that are single stranded and are used for the complementary building blocks of the target sequence

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15
Q

PCR requirements

A 
Magnesium chloride 
Buffer :Ph 8.3-8.8
DNTP 
Primer 
DNA polymerase 
Target DNA
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16
Q

PCR cycle

A

Denaturation
Primer annealing
Extension of DNA

17
Q

Number of cycles for DNA

A

25-40 cycles

18
Q

What is Taq

A

Thermus aquaticus, which is a microbe found in 176 F hot springs in yellow stone national forest

It produces an enzyme called DNA polymerase that amplifies the DNA from the primers by the polymerase chain reaction in the presence of Mg.

19
Q

What is another name for PCR

A

Thermocycler

20
Q

Phage allows distinction of

A

Living and dead bacteria

21
Q

How does phage detect bacteria rapidly

A

By measuring the activity of a reporter gene carried by a phage and expressed only after infection

22
Q

Biosensors

A

Detector based on selective molecular components of plants or animals

23
Q

Culture method detects only ?

Dead cells or viable cells

A

Viable cells

24
Q

What is ELISA

A

Technique used to detect (assay) specific molecules in samples

25
Q

Indirect ELISA detects

A

Ab

26
Q

Sandwich ELISA detects

A

Antigen

27
Q

Competitive ELISA detects

A

Antigen

28
Q

How many dyes does a real time PCR have

A

Fluorescent reporter dye

Quencher dye

29
Q

In real time PCR, the fluorescent dye is visible and turnt on in what stage ?

A

Extension

30
Q

2 species of bacteria that are used in fermentation of milk

A

Lactobacillus bulgaricus

Streptococcus Thermophillus

31
Q

What causes yogurt to thicken

A

Lactic Acid coagulase the remaining milk causing the yogurt to thicken

32
Q

What is a metabolic product of both bacterial species

A

Acetaldehye

33
Q

What does give raw yogurt its characteristic flavor

A

Acetaldehyde

34
Q

How long does the incubation of yogurt take?

A

12 hrs at 32 C

35
Q

Streptococcus thermophilus forms

A

Formic Acid
Co2
Drop Ph to 5.5

36
Q

In the process of cheese making , milk is treated with

A

Lactic acid bacteria and

Enzyme called rennin

37
Q

What is milk protein called

A

Casein

Micro (9 decks)

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