Food Microbiology Flashcards
What types of Microorganisms are there?
Bacteria Fungi - Yeast and Mould Viruses Protozoa Algae
What is Bacteria?
Bacteria are simple unicellular prokaryotic cells
What shapes do bacteria come in?
Sphere - Coccus
Vibrio - Comma
Bacillus - Rod
What condition provide variable growth characteristic
Temperature Acidity Presence of Oxygen - Anaerobic and aerobic Moisture or Salt Nutrient availability Time
What is yeast?
Yeast is a circular unicellular eukaryote cell
What is a mould?
Mould is a colonising multicellular eukaryote that are vegetative - they reproduce by producing spores.
What is a virus?
A virus is not a cell, it is viral coded genome that hijacks cells metabolic machinery to reproduce.
Why are cell membranes important?
Because they help facilitate movement across the membrane whilst ensuring unwanted particles and pathogens are kept out.
What is diffusion across cell membrane?
Diffusion relies on the substance being lipid soluble and small enough to fir through the pores of the cell membrane.
Across a phospholipid membrane what can limit movement?
Temperature, size of particle, gradient charge and lipid solubility.
What type of movements are available across a membrane?
Simple Movement Facilitated movement Active transport Osmosis endo and exocytosis.
What is simple movement?
A substance moves from higher concentration to a lower concentration.
What is facillitated movement?
Movement down a concentration gradient through the use of a carrier protein.
What is osmosis?
Water diffusion across membrane to maintain balanced gradient
What is active transport?
Active transport requires energy input to move a substance up a concentration gradient.
What are the two forms of metabolism?
Catabolism and Anabolism
What is Catabolism?
Catabolism is the break down of larger molecules into smaller ones with energy as a by product
What is Anabolism?
Anabolism is the method of building a larger molecule with the use of energy.
What are the three important fermentation pathways?
Homolactic, Alcoholic and Propionic these all relie on pyruvate.
What does homolactic fermentation do?
Converts Lactose into lactic acid.
What does alcoholic fermentation do?
Turns sugar into Alcohol and Co2
What does propionic fermentation do?
Produces propionic acid, acetic acid and CO2
Why do microorganisms like food?
Because food is complex and will usually have sufficient nutrients for MO growth
What is water activity?
Water activity is the presence of water that is not bound by the food material - essentially free water for microorganisms
What role does water activity play in heat treatment?
It is more efficient to treat a higher water activity with heat.
what range of water activity does highly perishable foods sit?
1.00 to 0.95.
What role does pH play with the growth of microorganisms?
Every microorganism has an optimal pH level for growth, the further you move away from this level the slower the growth becomes until it either hibernates or denatures the bacteria.
what role does temperature play with the growth of microrganisms?
Every microorganisms has an optimal temperature range for growth.
What type of microorganisms are classified by temperature?
Psychrophiles are cooler
mesophiles are regular temperature
thermophiles are hotter
how is energy produced in living cells?
It is produced by oxidising carbohydrates.
What are the two main forms of glucose catabolism?
Aerobic (glucose completely broken down) and Anaerobic(Glucose partially broken down).
What are the products of Aerobic catabolism?
It produces CO2 H2O and Energy
What are the products of Anaerobic catabolism?
Either (Lactic acid + Energy) or (Ethyl Alcohol + CO2 + Energy)
What is an enzyme?
An enzyme is a catalyst that allows a reaction between reactants to undergo at a much lower activation energy.
What is an enzyme made of?
Protein!
What doe anaerobic catabolism use instead of oxygen?
It uses other electron acceptors such as nitrate, sulfate and carbonate.
What is fermentation?
Fermentation is the anaerobic oxidation of sugars. It only involves glycolosis and it donates its electron energy to an organic molecule.
What is the pathway of homo-lactic fermentation?
Pyruvic acid is reduce by NADH to lactic acid
What is the pathway of alcoholic fermentation?
Pyruvic acid has CO2 removed to form acetaldehyde, the acetaldehyde is then reduced to ethyl alcohol.
How are hard cheeses ripened?
Using lactic acid bacteria to break down the lactose into glucose and galactose.
What factors can result in food spoilage?
Physical, Chemical and Microbial
What methods do we need to stop microbial pathogens infesting our food?
We need to prevent pathogen access, we need to inactivate pathogens and we need to prevent or slow growth if the other two methods fail.
How do we use temperature to inhibit microbial growth?
Chilling, freezing and pasteurising
how do we use water activity to inhibit microbial growth?
Drying, salting, curing
How do we use pH to inhibit microbial growth?
We can acidify or ferment
How do we use pressure to inhibit microbial growth?
We use cold pressure, vacuum pcakaging
what are some other ways to inhibit microbial growth?
Sterilisation and preservatives
what manufacture preservatives can we use to inhibit microbial growth?
Sulphites and Nitrites
What organic compounds can we use to preserve food?
Lactic acid, acetic acid, Sorbic acid and benzoic acid
How do weak acids work against microbes?
The acid enters the cell membrane and then dissociates into a charged anion and proton - this can disrupt the cell. the cell spends energy getting rid of the proton opposed to using the energy for growth.
What are some other types of food preservatives?
Chelator, natural microbials (oregano),
What pH is botulinum unable to grow?
Sub 4.5
Why do we use canning?
Because it is a form of commercial sterilisation - it sterilises the cans by introducing pressurised steam into a chamber
what are the common causes of foodborne illness?
Norovirus campylobacter listeria salmonella escherichia coli
what are the illnesses associated with meat, eggs and fish?
Salmonella, E coli and clostridium
what are the illnesses associated with fruit and veg?
Listeria monocytogenes
what are the illnesses associated with milk and dairy?
Salmonella and campylobacter
what are the illnesses associated with water?
Giardia
What are the pathogenic mechanisms of bacteria
They can produce toxins
they can damage walls
they can invade mucusol layers
they can invade the lymphatic system
What is campylobacter?
Gram negative thin rod bacteria - Campylobacter comes from raw milk, beef, poultry. It damages the epithelium and epithelial in the colon
What does campylobacter do?
campylobacter mimics appendicitis
what are the conditions for growth for campylobacter
grow at 30 to 46C, can survive 4C in moist conditions.
How to combat campylobacter
heat at 55 to 60C and dry your product
What is salmonella?
It is a Gram negative anaerobic rod. It invades the cells in the lower intestinal tract deforming the wall.
how do we combat salmonella?
They grow at 5.2 to 46 C, they can also survive freezing. we have to destroy by using heat and we can reduce pH to quicken this effect.
What is E. Coli?
gram negative rod anaerobe. it grows between 7 to 46C grows between 4.4 and 10pH but can survive much more acidic
