Chapter 6 MICROBIAL GROWTH Flashcards
(94 cards)
Factors affecting bacterial growth
- Physical
2. Biochemical/Nutritional
What are the physical factors that affect bacterial growth
pH, temperature, oxygen concentration, moisture, hydrostatic pressure, osmotic pressure and radiation
What are the nutritional factors that affect bacterial growth
Availability of carbon, nitrogen, sulfur, phosphorus, trace elements and in some cases vitamins
What are the 3 groups of microorganisms based on preferred range of temperature
- Psychrophiles
- Mesophiles
- Thermophiles
How many groups of psychrophiles are there
2
Psychotrophs
Is the other group of psychrophiles that can grow at 0°C with an optimal growth at 20-30°C. These cause low temperature food spoilage in the fridge
Psychrophiles
1st group has a strict hroth at 0°C with an optimal growth at 15°C. Found in oceans or polar regions.
Can psychotrophs survive subfreezing temperatures
Yes, they might become dormant and gradually decrease in numbers.
What are signs of food spoilage by psychotrophs
They slowly degrade food. Mold mycelium growth occurs, slime on food surfaces or off tastes or colors.
Mesophiles
Moderate temperature loving organisms. Optimum for growth at temperatures that humans favor; 25 to 40ﾟC ( 37ﾟC for pathogenic bacteria). Most common organism. These are the most common spoilage and disease causing organisms.
Thermophiles
Heat loving organisms capable of growing at high temperatures, with optimal growth at 50 to 60ﾟC. These temperatures are found in hot tap water, sunlit soil, thermal water such as Hot Springs. They cannot grow at 45ﾟC or lower.
Which microbes form and endospores and where are they usually found? Are they considered a public threat?
Thermophiles. They are heat resistant and may survive heat Tx of canned goods, spoiling food. Not considered a public threat.
What important role do thermophiles play in daily life
They play a role in organic compost piles where temperatures can rise rapidly to 50-60°C
Extreme thermophiles
These are made up of archaea microbes. Also known as hyperthermophiles. Their optimal growth is at 80°C or higher. They live in hot springs or volcanic sediment rich in sulfur.
Which microorganisms require nutrients rich in sulfar
Hyperthermophiles
What is the normal pH range for bacterial growth
6.5 to 7.5, few with pH of 4
What bacteria that can live in of pH 4 and what are they used for in daily life
Acidophiles. Food preserved from spoilage with bacterial fermentation such as sauerkraut, pickles and cheese.
What is the optimal pH for mold and yeast growth
pH 5 to 6
What type of pH inhibits microbial growth and is it used for food preservation
Alkalinic. Its rarely used to preserve foods.
What problem do bacteria cultured in the lab come across as far as pH is concerned? How is this addressed?
Bacteria often produce acids which interfere with their own growth. Chemical buffers are used such as phosphate salts which are non toxic and provide phosphorus which is an essential nutrient, and pep tones and amino acids are also used as buffers.
Where do microbes obtain most of their nutrients from
From solution of surrounding water. They require 80 to 90% for growth
How does high osmotic pressure affect bacterial cells
It can remove the necessary water from cell leading to plasmolysis. The cell growth is inhibited as plasma membrane pulls away from cell wall
What is plasmolysis
Shrinkage of cells cytoplasm
How is osmotic pressure used to persevere food
High salt and sugar draw water out leading to plasmolysis of microbial cells that are present and inhibiting growth. This is used for salted fish, honey, and condensed milk.
