24 Questions
What is characteristic of the lag phase in thermophilic growth?
It is short and sometimes difficult to measure
What is the typical duration of the logarithmic phase of growth in thermophiles?
Of short duration
What is the minimum generation time reported for some thermophiles?
10 minutes
What is characteristic of thermophilic microorganisms below their growth range?
Loss of viability or autosterilization
What is a factor that affects the heat resistance of microorganisms?
The presence of metal ions such as Mg2+
What can be inferred from Figure 7-2?
The growth curve of thermophiles changes with temperature
What is the main reason why high-protein-content foods require more heat processing than low-protein-content foods?
To achieve the same end results in terms of microbial control
What is the effect of pH on the heat resistance of microorganisms?
Lower pH increases heat resistance
What is a general characteristic of the death rate of thermophilic microorganisms?
It is rapid
What is a consequence of thermophilic microorganisms growing below their growth range?
Loss of viability or autosterilization
What is the primary mechanism of microbial control in intermediate-moisture foods?
Control of water activity
How does drying affect bacterial growth?
Drying inhibits bacterial growth
What is the main advantage of using heat processing as a food preservation method?
It can effectively control microorganisms
What is the purpose of adding salts to food?
To inhibit microbial growth
What is the effect of thermophiles on food?
They spoil food quickly
What is the primary goal of food preservation methods?
To extend the shelf life of food
What is the effect of increasing maximal growth temperatures on the G-C content of rRNA molecules?
It increases
What is the primary reason microorganisms and enzymes cannot be active in dried foods?
Lack of water
What is the water activity (aw) range for intermediate-moisture (IM) foods?
0.60-0.85
Why do bacteria play no role in the spoilage of dried foods?
They require aw values above 0.90
What percentage of water remains 'bound' to other constituents of the medium during freezing?
5-10%
What is the purpose of drying in food preservation?
To decrease microbial growth
What is the effect of dehydration on microorganisms?
It destroys some of them
What is the term for foods that contain between 15% and 50% moisture and an aw between 0.60 and 0.85?
Intermediate-moisture foods
Study Notes
Characteristics of Thermophiles
- Thermophilic growth has a short lag phase, sometimes difficult to measure, and rapid spore germination and growth.
- The logarithmic phase of growth is short-lived, with some thermophiles having generation times as short as 10 minutes at high temperatures.
- The rate of death or "die-off" is rapid, with loss of viability or "autosterilization" occurring below the thermophilic growth range.
Factors Affecting Heat Resistance of Microorganisms
- The binding of metal ions such as Mg2+ is an important factor.
- Wet proteins are susceptible to heat, with thermal breaking of peptides and protein denaturation rate depending on water binding capacity.
Heat Resistance
- Fatty acid chain length affects heat resistance, with longer chains being more resistant.
- Salts such as Ca2+ and Mg2+ affect heat sensitivity, with pH levels impacting heat resistance.
- The decimal reduction time (DRT) of Enterococcus faecalis is affected by pH levels.
Protein and Other Substances
- High-protein-content foods require more extensive heat processing than low-protein-content foods to achieve the same results.
- The G-C content of rRNA molecules increases with maximal growth temperatures, making the structure more stable through hydrogen bonding.
Food Protection by Drying
- Drying preserves foods by removing water, making it unavailable for microbial growth and enzymatic activity.
- Dried, desiccated, or low-moisture (LM) foods have a water activity (aw) between 0.00 and 0.60, while intermediate-moisture (IM) foods have an aw between 0.60 and 0.85.
- Most bacteria require aw values above 0.90 for growth, making them less likely to spoil dried foods.
This quiz covers the characteristics of thermophiles, including thermal death time and point, temperature, and D value. It's a great resource for microbiology and biology students.
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