Introduction Flashcards
What is CFU?
Colony forming unit
What is the most commonly used method for counting CFU/ml?
Turbidity measurment
What are the units for turbidity measurement?
Optical density
What does turbidity use to measure CFU/ml?
Scattered light
How do you calculate absorbance?
Log (incident light/transmitted light)
Negatives of turbidity
No difference between live or dead cells
Not reliable at low numbers
What is viable counting?
Using a dilution series to count cells
What does auxotrophic mean?
Microbes that can’t make a compound
What is D-value?
Time required to kill 90% of starting population for a concentration of biocide
How are biocides activated?
Contact with bacterial cell surface
What are the 6 classes of biocides?
Phenols
Alcohols
Halogens
Quaternary compounds
Metals
Oxidising agents
Examples of phenols
Carbolic acid and Lysol
Why aren’t phenols used in the food industry?
They leave a ‘taint’
Why are alcohols used in food production environments?
Detergent action
Lipid solvent
Protein denaturation
Ingredients in alcohol biocides
Methanol, ethanol and isopropanol
Why aren’t halogens used on metals?
Corrosion
Examples of halogens
Iodine
Tyrosine
Chlorine
Hypochlorous acid
Function of halogens
Oxidises cellular components
Function of quaternary compounds
Penetrate aqueous environments and targets lipids and proteins
Negatives of quaternary compounds
Very expensive
Function of metals as biocides
Combine with SH group of cysteine and used as algicide and fungicide
What is the main oxidising agent used?
Hydrogen peroxide
Function of oxidising agents
Sporicidal
Positives of oxidising agents
Residue free
Preservative in food treatment
Disrupts proteins
What needs to be considered when picking a biocide?
Surface
Amount of organic matter
Toxic residue possibility
Capsules
