Microbial Detection In Foods Flashcards Preview

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Flashcards in Microbial Detection In Foods Deck (37):
1

Reasons to detect microorganism in food

Food quality
Food safety
Legal requirement

2

Challenges in microbiological analysis of foods

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

3

Types of microbiological methods

Culture
Microscopic
Chemical
Physical
Biochemical
Molecular
Immunological

4

Detection methods

Conventional
Novel

5

Conventional method include

Culture method
Direct and indirect enumeration
Bacterial toxins
ELISA

6

Novel methods include

Immunogenetic separation
PCR and hybridization
Biosensor
Bacteriophage

7

Microbiological analysis steps

Sampling
Amplification
Detection
Confirmation

8

What is the principles of culture methods ?

Ability of microorganisms to grow in specific media

9

Limitations of culture methods

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

10

Basic steps for ELISA

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

11

What does ELISA plate reader measure?

It measures color density in plate well

12

What is PCR?

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

13

PCR target ?

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

14

What are primers

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

15

PCR requirements

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

16

PCR cycle

Denaturation
Primer annealing
Extension of DNA

17

Number of cycles for DNA

25-40 cycles

18

What is Taq

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

What is another name for PCR

Thermocycler

20

Phage allows distinction of

Living and dead bacteria

21

How does phage detect bacteria rapidly

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

22

Biosensors

Detector based on selective molecular components of plants or animals

23

Culture method detects only ?

Dead cells or viable cells

Viable cells

24

What is ELISA

Technique used to detect (assay) specific molecules in samples

25

Indirect ELISA detects

Ab

26

Sandwich ELISA detects

Antigen

27

Competitive ELISA detects

Antigen

28

How many dyes does a real time PCR have

Fluorescent reporter dye
Quencher dye

29

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

Extension

30

2 species of bacteria that are used in fermentation of milk

Lactobacillus bulgaricus
Streptococcus Thermophillus

31

What causes yogurt to thicken

Lactic Acid coagulase the remaining milk causing the yogurt to thicken

32

What is a metabolic product of both bacterial species

Acetaldehye

33

What does give raw yogurt its characteristic flavor

Acetaldehyde

34

How long does the incubation of yogurt take?

12 hrs at 32 C

35

Streptococcus thermophilus forms

Formic Acid
Co2
Drop Ph to 5.5

36

In the process of cheese making , milk is treated with

Lactic acid bacteria and
Enzyme called rennin

37

What is milk protein called

Casein