Chapter 17: Fermentation: Desirable Effects of Microorganisms Flashcards
Define microbiology.
the study of living organisms too small to be seen by the unaided human eye
Define microorganisms.
Organisms that are only visible through a microscope
What are the characteristics of microorganisms?
They multiply rapidly, and transfer easily from one surface to another (cross- contamination)
What is cross-contamination?
transfer easily from one surface to another (cross- contamination)
What are the microorganisms that have positive use in foods?
bacteria, yeasts, and molds
Bacterias are members of what kingdom? Yeasts and molds?
Bacteria: Monera
Yeasts + molds: Fungi
What do microorganisms depend on to grow and multiply?
Outside sources
Are bacteria single-celled or multiple-celled?
single-celled organisms
How does bacteria multiply?
Cell division
Describe the cells of bacteria?
Their cells have no nucleus and are filled with a gelatinous liquid called cytoplasm
How long is bacteria?
3 micrometers long
How is bacteria classified?
by shape, cell wall structure, and oxygen needs
Name the 3 basic shapes of bacteria.
– Bacilli have a rod shape
– Cocci have a spherical shape
– Spirilla have a spiral shape
Name the 2 types of cell wall structures of bacteria.
- Gram-positive bacteria turn violet
- Gram-negative turn red
How are the cell wall structures of bacteria identified?
by the ability to be stained by a crystal violet dye, called Gram’s stain
Name the 3 categories of bacteria based on oxygen needs.
– Aerobic bacteria must have oxygen to function
– Anaerobic bacteria function best in an oxygen-free environment
– Facultative bacteria can function in either type of environment
What kind of bacteria spoils cabbage? What prevents the aerobic bacteria to grow?
- Aerobic bacteria
- submerging cabbage in salt water does not
allow aerobic bacteria to grow
Aerobic bacteria in cabbage can multiply and develop what?
the flavor and texture of sauerkraut
What do bacterial growth rates depend on?
pH, air, temperature, and nutrients
Define fungus.
a plant that lacks chlorophyll
Are fungi single-celled? Do they have a nucleus?
– are not always single-celled
– have a nucleus in their cells
What is the function of fungus in nature?
widely distributed in nature and help organic matter decay
Give examples of fungus.
mushrooms, molds, mildew, rust, and yeast
How is fungi classified?
by their structure and reproduction methods
The basic structure of fungi is made of what?
made of filaments or tubes called hyphae
Describe the structure of hyphae.
have elongated cells or chains of cells that absorb nutrients from the environment
How is myecelium formed?
Hyphae intertwines and forms a branched network
How does myecelium reproduce?
by creating spores
Define spores.
the reproductive cells of fungi
How do spores develop?
in a sac- or balloon-like structure that explodes when full
How big are spores? What are they resistant to?
Spores are microscopic and resistant to harsh environments
Define molds.
fungi that form a mycelium structure with a fuzzy appearance
What do molds produce? What do they do?
Many produce antibiotics that kill bacteria likely to be growing in the same area
Define yeasts.
fungi with a single-celled structure
What do yeasts produce?
produce alcohol and carbon dioxide
What do yeasts form on soil or plants? What do they form in animals?
Soil or plants: mycelium structures
Animals: reproduce by budding
Name 4 common characteristics of microorganisms.
– grow rapidly and are good sources of edible
protein for animals
– can enhance or add to the nutritional value of food
– can enter a dormant or inactive state to protect themselves from a harsh environment
– reproduce when the environment supports growth needs
Define a pure culture.
a large volume of one type of microbe grown purposely
What are microorganisms used for in food processing plants?
development of such foods as pickles, cheese, and beverages
Define starter cultures.
pure cultures of microorganisms that are added to foods to begin a fermentation
Define microbial enzymes.
Enzymes produced by microorganisms
What is the source of most changes in food products?
Microbial enzymes
How do microbial enzymes act in the body?
– Microorganisms excrete digestive enzymes to break down large macromolecules for transport through the microbial cell wall
– Microorganisms can then absorb the fragments and use them for energy
How can microorganisms be classified
by the organic molecules they use as a food source
What are proteolytic microorganisms?
release proteases that change proteins into amino acids and are used to clot milk, tenderize meat, and remove pulp from cacao beans
What are lipolytic microorganisms?
produce enzymes that digest fats and are used to flavor cheese, remove egg yolk, and clean up oil spills
How are microorganisms classified in terms of their scientific names?
By 2 Latin names
- The genus name
- The species name
What are characteristics of the genus name?
– is always capitalized
– indicates a family of organisms that have similar characteristics
What are characteristics of the species name?
– is never capitalized
– identifies the type of microbe within the family
Name the 4 factors that affect microbe growth.
- Microorganisms need an energy supply
- Microorganisms need water
- Microorganisms grow at certain pH values
- Microorganisms prefer a moderate temperature
What are microorganisms composed of chemically?
composed of carbon, oxygen, nitrogen, and hydrogen
What do microorganisms need to feed on?
- C, O, N, H
- Minerals and vitamins to aid with enzyme activity
Can microorganisms be dormant? In what conditions?
Some microorganisms can remain alive, but
dormant, in dried conditions
What is a safe water activity for most food storage?
0.70 or lower
How can water activity be lowered?
by removing water, adding solutes, or by freezing
What are the 3 pH levels that microorganisms can live in?
Minimum, preferred, maximum
What temperature do microorganisms prefer?
Modertate temp
Why don’t microorganisms like freezing? And heating?
Freezing: slows enzyme activity and cell reproduction
Heating: can kill microorganisms
When do microorganisms die if temperature is raised?
at 5 C to 12 C above the temperature for maximum growth
Define fermentation.
enzymatically controlled change in a food product caused by the action of microorganisms
The changes from fermentation result from what?
– digestive enzymes released by the
microorganisms
– the release of by-products, such as carbon dioxide, acetic and lactic acids, and ethanol
What is the primary product of a microbial reaction?
Energy
What can by-products of microbial reactions change in a food?
color, texture, flavor, aroma, and pH
When does fermentation occur?
when nutrients broken down by digestive enzymes are absorbed by microorganisms for growth and energy
What is yeast needed in?
all yeast breads, alcoholic beverages, and vinegars
What is often used for yeast?
Saccharomyces cerevisiae
What is the main source of energy of Saccharomyces cerevisiae?
– Sugar is its main source of energy
– It can utilize on honey, molasses, or corn syrup
What steps is yeast affected by in the bread-making process?
– Warm liquid activates yeast
– Mixing distributes yeast evenly
– Kneading the dough develops the gluten
- Proofing
What does proofing allow? What does it release?
- Allows the yeast to produce enzymes that break down sugars
- Releasing alcohol and carbon dioxide
What happens during the bread making process?
– carbon dioxide becomes trapped in pockets throughout the dough, gluten stretches, and the dough rises
– the dough continues to rise during baking and a crust forms
What do bread products contain?
flour, yeast, salt, and water
What is wine?
fermented juice of plant products such as grapes, honey, various fruits and dandelions
What can be added to inhibit unwanted microbe growth?
Sulfur dioxide (SO2) or potassium metabisulfite
How are wine juices kept? For how long?
held in anaerobic conditions for up to 4 weeks in oak barrels or stainless steel tanks
When is wine fermentation complete?
when bubbling from CO2 production stops
How is wine aged?
in barrels or vats to slowly develop the characteristic flavors
Give examples of yeast fermentation in other alcoholic beverages.
– Beers are made from fermented barley
– Bourbon is made from corn
– Rum is made from sugar cane or molasses
– Brandy is distilled wine or fermented fruit juice
– Liqueurs have a brandy base with sugar and flavorings added
Name the 3 main types of bacterial fermentation.
1) Lactic acid fermentation
2) Proteolytic
3) Acetic acid fermentation
What is lactic acid fermentation?
Fermented foods produced by bacteria whose by-product is lactic acid
Produces the other by-products of acetic acid, formic acid and carbon dioxide
What does sauerkraut result from?
the lactic acid bacterial fermentation of cabbage submerged in brine, a salt and water solution
What does brine do in sauerkraut?
The salt controls water activity and pulls water with dissolved sugar and nutrients to the surface
What does bacteria do in sauerkraut?
Bacteria utilize the sugar and release carbon dioxide and lactic acid into the brine
How are cucumbers turned into pickles?
heating them in a spiced vinegar solution, refrigerating in an acid brine, or fermenting them with lactic acid bacteria
What does commercial pickling involve?
– washing the cucumbers in a chlorine solution
– placing them in a brine with a pure culture of Lactobacillus (starter culture)
Which other foods can be pickled?
vegetables such as watermelon rinds, beets, cauliflower, okra, and onions, and even eggs
How can lactic acid fermentation be used in meats?
to make dry and semidry sausages
What does lactic acid fermentation provide in meats?
– Increased acid tenderizes the meat and adds a tart flavor
– Fermentation, smoking, and drying prevent spoilage
How does cheese form curds?
Milk is pasteurized, then rennin and lactic acid bacteria are added to form curds
How is the whey separated from the curd?
– Curds are cut into small cubes and heated to help the whey separate from them
– Whey is drained off and collected for use as an additive in other processed foods
What can cheese curds turn into?
– mixed with cream to make cottage cheese
– put in presses to squeeze out excess moisture for making aged cheese
What happens during aging or ripening of cheeses?
cheeses wrapped with wax are placed in curing rooms
What is responsible for the characteristic flavour of cheeses?
Different bacteria or molds
What does the sharpness of cheese refer to?
refers to the strength of flavor and aroma
How does the sharpness of cheeses develop?
Develops as cheese ages
Cheeses that age longer tend to what?
– have firmer consistency
– have more crumbly textures
– melt into sauces more readily
What by-products do molds create?
antibiotics, flavor compounds, and enzymes
Name some examples of fermented foods often used in Asian cuisine.
– soy sauce, a fermented mix of soybeans and wheat
– tempeh, a soybean cake of cooked, mashed soybeans pressed into blocks, inoculated with Rhizopus molds, and wrapped in banana leaves
What is two-step fermentation?
uses bacteria as well as fungi to produce the product
Describe the two-step fermentation process of cheeses?
lactic acid bacteria is needed to form the product, then other microorganisms develop the flavors and textures
Describe the two-step fermentation process of sourdough bread?
lactic acid bacteria ferments the product, and then a yeast starter proceeds to ferment the product
east releases alcohol as they break down sugars, what follows yeast fermentation?
Acetic acid fermentation
What does Acetobacter bacteria use as energy? What does it release?
- Alcohol
- Releases acetic acid
What is produced by acetic acid fermentation?
Vinegar
How is acetic acid fermentation used in baked goods?
produces candied citron from citron lemons
How is acetic acid fermentation used in chocolate?
turns cacao beans into chocolate
Name 2 benefits of fermentation.
- Microorganisms help preserve some foods
* Fermentation offers a wider range of food options
How do microorganisms help preserve some foods?
Fermented foods tend to have a low pH and can be stored for longer periods (especially at refrigerated temperatures)
What does the variability of nutritional changes in fermented foods depend on?
– microorganisms used
– other ingredients added
– impact of fermentation on bioavailability
The concentrations of which nutrients are higher in cheese than in milk?
Fat and calcium
At what pH are bacteria killed? At what pH are molds killed?
Bacteria: 4.6
Molds: 1.5
