Microbial Detection In Foods Flashcards
Reasons to detect microorganism in food
Food quality
Food safety
Legal requirement
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
Types of microbiological methods
Culture Microscopic Chemical Physical Biochemical Molecular Immunological
Detection methods
Conventional
Novel
Conventional method include
Culture method
Direct and indirect enumeration
Bacterial toxins
ELISA
Novel methods include
Immunogenetic separation
PCR and hybridization
Biosensor
Bacteriophage
Microbiological analysis steps
Sampling
Amplification
Detection
Confirmation
What is the principles of culture methods ?
Ability of microorganisms to grow in specific media
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
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
What does ELISA plate reader measure?
It measures color density in plate well
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
PCR target ?
Sequence of DNA on each end of the region of interest which can be a complete gene or a small sequence
What are primers
Primers are 15-30 nucleotides that are single stranded and are used for the complementary building blocks of the target sequence
PCR requirements
Magnesium chloride Buffer :Ph 8.3-8.8 DNTP Primer DNA polymerase Target DNA
PCR cycle
Denaturation
Primer annealing
Extension of DNA
Number of cycles for DNA
25-40 cycles
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.
What is another name for PCR
Thermocycler
Phage allows distinction of
Living and dead bacteria
How does phage detect bacteria rapidly
By measuring the activity of a reporter gene carried by a phage and expressed only after infection
Biosensors
Detector based on selective molecular components of plants or animals
Culture method detects only ?
Dead cells or viable cells
Viable cells
What is ELISA
Technique used to detect (assay) specific molecules in samples
Indirect ELISA detects
Ab
Sandwich ELISA detects
Antigen
Competitive ELISA detects
Antigen
How many dyes does a real time PCR have
Fluorescent reporter dye
Quencher dye
In real time PCR, the fluorescent dye is visible and turnt on in what stage ?
Extension
2 species of bacteria that are used in fermentation of milk
Lactobacillus bulgaricus
Streptococcus Thermophillus
What causes yogurt to thicken
Lactic Acid coagulase the remaining milk causing the yogurt to thicken
What is a metabolic product of both bacterial species
Acetaldehye
What does give raw yogurt its characteristic flavor
Acetaldehyde
How long does the incubation of yogurt take?
12 hrs at 32 C
Streptococcus thermophilus forms
Formic Acid
Co2
Drop Ph to 5.5
In the process of cheese making , milk is treated with
Lactic acid bacteria and
Enzyme called rennin
What is milk protein called
Casein
