Podcast
Questions and Answers
What is characteristic of the lag phase in thermophilic growth?
What is characteristic of the lag phase in thermophilic growth?
- It is long and well-defined
- It is short and sometimes difficult to measure (correct)
- It is absent in thermophilic microorganisms
- It is temperature-independent
What is the typical duration of the logarithmic phase of growth in thermophiles?
What is the typical duration of the logarithmic phase of growth in thermophiles?
- Variable among thermophiles
- Several hours
- Several days
- Of short duration (correct)
What is the minimum generation time reported for some thermophiles?
What is the minimum generation time reported for some thermophiles?
- 10 minutes (correct)
- 30 minutes
- 2 hours
- 1 hour
What is characteristic of thermophilic microorganisms below their growth range?
What is characteristic of thermophilic microorganisms below their growth range?
What is a factor that affects the heat resistance of microorganisms?
What is a factor that affects the heat resistance of microorganisms?
What can be inferred from Figure 7-2?
What can be inferred from Figure 7-2?
What is the main reason why high-protein-content foods require more heat processing than low-protein-content foods?
What is the main reason why high-protein-content foods require more heat processing than low-protein-content foods?
What is the effect of pH on the heat resistance of microorganisms?
What is the effect of pH on the heat resistance of microorganisms?
What is a general characteristic of the death rate of thermophilic microorganisms?
What is a general characteristic of the death rate of thermophilic microorganisms?
What is a consequence of thermophilic microorganisms growing below their growth range?
What is a consequence of thermophilic microorganisms growing below their growth range?
What is the primary mechanism of microbial control in intermediate-moisture foods?
What is the primary mechanism of microbial control in intermediate-moisture foods?
How does drying affect bacterial growth?
How does drying affect bacterial growth?
What is the main advantage of using heat processing as a food preservation method?
What is the main advantage of using heat processing as a food preservation method?
What is the purpose of adding salts to food?
What is the purpose of adding salts to food?
What is the effect of thermophiles on food?
What is the effect of thermophiles on food?
What is the primary goal of food preservation methods?
What is the primary goal of food preservation methods?
What is the effect of increasing maximal growth temperatures on the G-C content of rRNA molecules?
What is the effect of increasing maximal growth temperatures on the G-C content of rRNA molecules?
What is the primary reason microorganisms and enzymes cannot be active in dried foods?
What is the primary reason microorganisms and enzymes cannot be active in dried foods?
What is the water activity (aw) range for intermediate-moisture (IM) foods?
What is the water activity (aw) range for intermediate-moisture (IM) foods?
Why do bacteria play no role in the spoilage of dried foods?
Why do bacteria play no role in the spoilage of dried foods?
What percentage of water remains 'bound' to other constituents of the medium during freezing?
What percentage of water remains 'bound' to other constituents of the medium during freezing?
What is the purpose of drying in food preservation?
What is the purpose of drying in food preservation?
What is the effect of dehydration on microorganisms?
What is the effect of dehydration on microorganisms?
What is the term for foods that contain between 15% and 50% moisture and an aw between 0.60 and 0.85?
What is the term for foods that contain between 15% and 50% moisture and an aw between 0.60 and 0.85?
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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.
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