food microbiology: intrinsic and extrinsic factors.

resistant to pasteurisation
lysozyme present in egg whites, ______________, hydrolytic enzyme, prevention , of late blowing in cheese
exogenous antimicrobial constituents include chemical preservatives such as sorbates, ______________, nitrite, etc
food preservatives ______________: fruit pieces, of dried fruits, wine and some meat products
, nitrite
food preservatives ______________: cured meats
acids (lactic, citric, phosphoric)
food preservatives______________: acidulents for low pH sauces, mayonnaise, dressing, fruit drinks
food preservatives ______________: cheeses, syrups, cakes, dressings
food preservatives ______________: bread, cakes, cheese, grain
food preservatives ______________: pickles, soft drink, dressings, fish marinades
food preservatives ______________: bakery products and fruit products
relative humidity
environmental factors include: temperature, ______________ and gaseous environment
gas phase
relative humidity and water activity are interrelated, thus relative humidity is essentially a measure of the water activity of the ______________
transfer from the gas phase to the food
when food commodities having a low water activity are stored in an atmosphere of high relative humidity Water will ______________
______________ May Eckardt on surfaces, giving rise to localised regions of high water activity
increase the water activity
. Once organisms have started to grow and become visible to lead active, they usually produce water as an end products of respiration. thus they ______________of their own immediate environment so that eventually microorganisms requiring a high water activity are able to grow and spoil a food which was initially considered to be microbiologically stable
lose water and become flaccid
the storage of fresh fruits and vegetables requires very careful control of relative humidity. If it is too low and many vegetables will______________. If it is too high then condensation may occur and microbial spoilage may be initiated
carbon dioxide and temperature
______________ effect the shelflife of blue smoked cod significantly. At a temperature of -1.5°C cod stored in air has a shelflife of 28 days or 14 days if stored at 3°C
if stored in a vacuum at -1.5°C . The fish has a shelflife of 35 days or 14 days is stored at 3°C . When the fish is stored in carbon dioxide is shelflife at -1.5° C is increased to 113 days or 49 days if stored at 3°C
oxygen comprises 21%
gaseous atmosphere: taster of the Earth's atmosphere and is the most important gas in contact with food, under normal circumstances
redox potential
the presence of oxygen and its influence on ______________ are important determinants of microbial associations that develop and their rate of growth
modified atmosphere packaging
the inhibitory effect of carbon dioxide or microbial growth is applied in ______________ of food and is an advantageous consequence of its use at elevated pressures (hyperbaric) in carbonated mineral waters and soft drinks
moulds and oxidative gram negative bacteria
carbon dioxide is not uniform in its affect on microorganisms ______________ our most sensitive and gram positive bacteria, particularly lactobacilli tend to be the most resistant.
some ______________ also show considerable tolerance to high carbon dioxide levels and dominate the spoilage microflora of carbonated beverages
increased solubility of carbon dioxide
growth inhibition is usually greater under aerobic conditions than anaerobic and the inhibitory effect increases with the decrease of temperature, presumably due to the ______________ At lower temperatures
the mechanism of carbon dioxide inhibition is a combination of several processes, including the effect of carbon dioxide on ______________
bicarbonate anions antiprotons
carbon dioxide dissolves in water to produce carbonic acid, which partially disssociates into ______________
weak dibasic acid
carbonic acid is a ______________ (pKa 6.37 and 10.25). In an unbuffered solution, it can produce an appreciable drop in PH. Distilled water in equilibrium with the CO2 in the normal atmosphere will have a pH of about 5. But the effects will be less pronounced in buffered food media so that equilibrium of milk with 1 atmosphere pCO2 decreased the PH from 6.6 to 6.0
weak organic acids
carbon dioxide can act in the same way as ______________ penetrating the plasma membrane and acidifying the cell's interior
physiological properties of the plasma membrane
carbon dioxide is also thought to cause changes in the ______________ adversely affecting solid transport; inhibition of key enzymes, particularly those involving carboxylation/decarboxylation reactions in which carbon dioxide is a reactance; and reaction with protean amino groups causes change in their properties and activities
respond to their environment
implicit factors are properties of the organisms themselves and how they ______________and interact with one another
specific growth rate
at its simplest an organisms ______________ can determine its importance in food's microflora; those with the highest______________ are likely to dominate over time
bacteria and are therefore outcompeted
specific growth rates is dependent upon the conditions prevailing; many moulds can grow perfectly well on fresh foods such as meat, but they grow more slowly than ______________
reduced pH or water activity
in foods where the faster growing bacteria are inhibited by factors such as ______________, Moulds Will assume an important role in spoilage
(Ks) affinity, lower Ks (higher affinity)
alternatively team organisms may have similar maximum specific growth rates, but differ in their ______________ for a growth limiting substrates. If the level of that substrate is sufficiently low that it becomes limiting than the organism with the ______________ will outgrow the other
exponential growth phase cells
______________ or almost always killed more easily by heat, low pH or antimicrobials than stationary phase cells, and often the faster their growth rates are more readily they are killed
finely balanced
at higher growth rates where the cell activity is greater and more ______________the damage caused by a slight jolt the system will be more severe than the same perturbation in cells growing very slowly or not at all
oxidative burst
the precise mechanism leading to cell death is almost certainly very complex one proposal is that lethal damage is largely a result of an ______________, the production of large numbers of damaging free radicals within the cell in response to the physical or chemical stresses applied. This would mean that cell death is in fact a function of the organisms response to stress rather than a direct effect of stress itself
grow for holding organisms such as ______________at higher temperatures has been shown to increase the heat resistance preexposure to moderately low PH can increase an organism subsequently resistance to a more severe acid challenge
reduce the minimum temperature
growth at progressively lower temperatures can ______________at which an organism would otherwise grow
gene transcription and protein production
some reaction to stress can be apparent very soon after exposure as existing enzymes and membrane protein sensor reacts to change. Other responses occur more slowly, since they involve ______________
heat shock proteins
the production of ______________; proteins produced following exposure to elevated temperatures at which protect themselves from heat damage. Some ______________described as chaperones chaperonins interact with on folded or partially unfolded proteins and assist them in reaching their correct conformation.
sigma factor
heat shock proteins or encoded by genes which have a specific ______________. ______________ are proteins which bind to DNA dependent RNA polymerase enzyme that transcribes DNA into mRNA. Rundowns who polymerase I 1st visited a certain class of DNA, and thus help determine which regions of the genome are transcribed
an alternative sigma factor ______________ aka the stationary phase, in fact is produced in cells throughout growth but is rapidly degraded in exponential phase cells. As growth slows at the end of exponential phase in accumulates and direct transcription of a battery of genes associated with the stationary phase many of which are protective
General stress response regulator
RpoS is a ______________and also accumulate in response to environmental stressors such as local H and osmotic stress. Since the ______________ confers resistance to a range of stresses, exposure to one factor such as low pH can confer increased resistance to other stressors such as heat. Rpos may also be associated with regulating expression of genes for virulence in some foodborne pathogens and such virulence factors, expressed as cells into stationary phase can also be induced by stress
______________ when growth of one organism stimulates the growth of another is well illustrated by the interaction of the starter cultures in yoghurt fermentation. Similar stimulatory effects can be seen in spoilage associations or in sequences of spoilage organisms seen when growth of one organism paves the way for others
less xerophilic Moulds
grain water activity may be sufficiently low to put fence. The growth of all but a few fungi Once these begin to grow, however water produced by their respiration increases the local water activity allowing ______________ to take over
degrading a food components
alternatively one microorganism might increase the availability of nutrients to others by ______________ such as starch or protein into more readily asimilable compounds
inhibitory component
mutualistic microorganisms may remove an ______________ and thereby permit the growth of others
allowing less acid tolerant organisms
mutualistic microorganisms there are able to remove inhibitory components have the safety implications in mould ripened cheeses, where mould growth increases the pH ______________ such as Listeria monocytogenes to grow
alternatively microorganisms may be Haystack towards one another, producing inhibitory compounds or sequestering essential nutrients such as iron, e.g. in lactic fermented foods
sub optimal factors
in some foods, microorganisms express a whole battery of ______________which collectively determine the food characteristics as a medium for microbial growth
hurdle effect, hurdle
the ______________ is best described: where each inhibitory factor can be visualised as a ______________ contributing to a food's overall stability and safety
aggregate effect of all the barriers at once
hurdled effect . In reality, microbes are usually faced with the ______________and it is this which determines whether the organisms can grow or how fast they can grow
storage, distribution, temperature abuse
to test the hard facts. The organism of concern is inoculated into the food material and its fate followed through simulated conditions of processing, ______________or whatever is required. Although it provides reliable data, the challenge trial is expensive, time consuming and labour intensive to perform properly. It also has extremely limited predictive value since its predictions hold only for the precise set of conditions tested
mathematical models
hurdle challenge: the most popular approach is to use ______________. a ______________ is simply an object or concept that is used to represent something else, and is constructed using mathematical concepts such as Constance, variables, functions and equations etc
probabilistic models
______________ give a qualitative assessment of the chance that a particular microbiological event will occur within a given time and are most suited to situations where the hazard a severe. The event, most often described in such models is the probability of toxin formation by Clostridium botulinum. The model describes the relationship between the probability of toxin production and the level of factors/variables present
nitrate, incubation temperature and salt
the toxin production model of the different factors included in the model it can be seen that ______________are more important in preventing toxin production than the others and that they are acting independently; there is no evidence of synergistic interaction between factors