L29/30 Flashcards
what is food mcirobiology
- study of microbial ecology under food related conditions
-concerned with regulating rates of change- conservation- minimising rates of change
-processing- encouraging rapid rate of change
- conservation- minimising rates of change
-note that eliminating mcirobes does NOT nessarily prevent spoilage, as microbial metabolic products may be significant in spoilage
routes of infection
- direct (organisms commonly found in environment)
- secondary (uncommon organisms, can contaminate via this route (e.g. bird dissemination of salmonella)
-processing inefficiencies (plant layout- predispose to contamination, e.g. botulism, or handling e.g. e.coli)
can be infected at stages of manufacturing: rae materials, stored materials, preparation, processing, packing, distribution, retail, consumption
explain the tracing of the origin of contamination
-outbreak: 2 or more people fall ill after eating same food
- local (food poisoning after restraunt meal): illness at same time, easy to identify where from
- widespead: illness in widely seperated areas, illness staggered over time, e.g. factor product, harder to detect
-disease surveillance- reportable diseases
resvoirs of infection- animal, soil, vegetation
types of illnesses
-intoxication: ingest preformed toxins (e.g. s.aureus toxins), short incubation before illness
- toxiocoinfection (non invasive infection): viable bacteria ingested, leads to colonising intestinal lumen, leads to enterotoxin production, acts locally e.g. cholera
-infection (invasive infection): invades intestinal epithelial cells, remains in gut but can spread further, e.g. salmonella
symptoms of nausea and diarrhoea
nausea- contration of abdonminal muscles
diarrhoea- chang einf requency, consistent, and volume fo faeces
explain effect of pH on contamination
- lower pH (less then 5.5) = more safe, stops bacterial growth due to organic acids
-Outside cell, organic acids break apart easily+ join back together constantly, when separate (can’t go into cell), but when together, can go into cell (at LOW pH, 3,4), as increase pH outside, more separate, so less get inside
Now its inside cell (undissociated), cell pH is 7, now equilibrium favours separation (dissociates), now have hydrogen ions, cell does not want free hydrogen ions because it lowers pH, so it uses a ATPase pump to grab the hydrogen ions and spit it out (using ATP, energy of the cell)
This means doesn’t have the energy to replicate, so lower the pH can stop cells from doing the stuff the need to do to survive
principles of food preservation
- prevent damage by animals and insects
- retard chemical changes: metabolic products, catabolism
-prevent or delay microbial decomposition: metabolic activity, byproducts
-enhance growth of specific microbes: fermented foods: pickles, cheese, biochemicals: fructose from corn starch, citric acid via fungus
approaches to food preservation
-nutrient limitation: canning, vacuum sealing
-pH contorl: pickling, fermentation
- water activity: dehydration, adding salt
-preservation: nitrites, inhibts growth
-temp.: refridgeration, freezing, cooking, canning
food ecosystems
- different food = different ecosystems = different bacteria
e.g.
staphylococcus- grow at low aw (salty, sugar food)
-salmonella- grow in meat + poulty
how is food production controlled
- hazard analysis critical contorl point
hazard: source of danger
risk: likely occurance of danger
CCP: control microbial hazard bacteriocidal - standards, max. counts
-testing: sampling + isolation method
what is the hurdle effect
- additive/syngergistic effect of different preservation methods
When I have 1 form of control, band it’s insufficient so microorganism jumps th hurdle
If have 2 different things, some of them can’t jump over both, but 1 might get buy
E.g. bacteria need to grow to a certain level, to start spoilage
E.g imagine having a bacteria, can grow at certain water content, temp., and pH, if increase 1, can jump over it, but increase all, and wont be able to
e.g. low heat < 100 degrees: can germinate spores (heat shock), addition of NO2, NaCl, or loweing pH to 4.5 -> no germination,
low aw: s.aureus gros at 0.86 at high pH, if pH 4.6, wont grow at Aw 0.93
HPP: bactericidal effect icnreased with mild heat, slightly low pH, lysozyme
fresh meat
- has essential nutrients for human
-usually free of spoilage or pathogens unless contaminated
-prions more of a issue then viruses, yeasts, and molds - bacteria present from surface of animal or from intestinal tract
e.g. salmonella, staphlococcus auerus, usually at low no. but potential for outgrow if processing/storage abuse occurs
production processes
- insection of live animals
HACCP commonly applied
pre + post slaughter washes, to eliminate/minimise faecalc ontamination
post production (consumer) activities: refrigeration, freezing (effective in killing parasites), cooking
explain the use of nitrites
- used as sodium nitrite, inhibt growth + toxin production of c.botulinum on cured meat: inhibts outgrowth of germianted spores, high concs. needed
- many othe rhurdles add to its effectiveness: low pH, anerobic conditions,k reduced water activity
-inhibts other (non spore forming) microorganisms by inactivating enzymes
- used on variety of meat products: bacon, ham , fermented sausages
explain modified atmosphere packaging: MAP
- same principle as controlled atmosphere storage
in meats:
-packaged goods flushed with modified atmosphere
-packaging has low permeability, so atmosphere maintained until opened- aerobic spoilage organisms, such as pseudomonas, inhibited
-LABs become dominant flora, slower growing + generally less offensive
- aerobic spoilage organisms, such as pseudomonas, inhibited
