Food and Spoilage Flashcards
Why do we care about food microbiology
Large impact on economic market & largely consumed
* Alcoholic beverages
* Fermemented food
Respiration vs Fermentation
- Respiration externally-derived electron acceptor, either O2 (aerobic) or some other oxidant (CO2, sulfate - anaerobic)
- Fermentation: redox reaction in the absense of an added electron acceptor - endogenous organic electron acceptor = using something already in the cell
2 major types of fermentation
lactic acid & ethanolic
What are the three genera (genus) that use pyruvate to make important products for fermentation
- Aspergillus: lactic acid
- Lactobacillus: lactic acid
- Saccharomyces: ethanol, CO2
Why are fermented foods so common
- Preservation of food
- Improved digestibility
- Addition of nutrients and flavors
Cacoa seeds are fermented by:
3 things
- yeasts
- lactic acid bacteria
- acetic acid bacteria
The process of cacoa bean fermentation depends entirely on what type of microbial fermentation
Indigenous microbial fermentation - microbes that are naturally present on the cocoa beans and their surrounding environment
Microbial succession during cocao fermentation
- Yeast (day 1-2): degrade pectin; ferment sigars and citrate to ethanol and acetate
- **Lactobacillus **(day 2-4): ferments sugars to lactate and acetate
- Acetobacter (day 4): oxidizes ethanol
Traditional ____ were used to start fermentation of soy and other products, today ____ are used
indigenous microbes; starter cultures
What does Aspergillus oryzae ferment
Soy products
* miso
* soy sauce
Saccharomyces cerevisiae
“Brewer’s yeast” or “baker’s yeast”
* involved in the fermentation/production of bread, beer, and wine
Which of the following is the best definition of a “yeast”?
a) Saccharomyces cerevisiae.
b) Beer and bread making Fungi.
c) Unicellular growth of a fungus.
d) Filamentous growth of a fungus.
e) Any single-celled Eukaryote.
c) Unicellular growth of a fungus.
Energy metabolism process for Saccharomyces cerevisiae (S. cerevisiae) in aerobic conditons
Aerobic respiration: complete breakdown of glucose into carbon dioxide and water, releasing energy in the form of ATP (high energy pathway)
Energy metabolism process for Saccharomyces cerevisiae (S. cerevisiae) in anaerobic conditons
Anaerobic fermentation (glycolysis + alcohol fermentation) Less efficient than aerobic respiration, yielding only 2 ATP molecules per glucose molecule
3 steps in anaerobic fermentation of sugar to ethanol & CO2 in S. cerevisiae
- Glycolysis
- Pyruvate to acetaldehyde by pyruvate dehydrogenase
- Acetaldehyde to ethanol by alcohol dehydrogenase
How is fermentation by Saccharomyces used to make bread
employs the CO2 used during fermentation: the alcohol is baked off & CO2 is responsible for leavening the bread causing it to rise as gas gets trapped
When does wine making date back to; how did it compare to water at that point
evidence for wine making dates to ~6000 BC
* safer to drink than water, before filtration and refrigeration
Primary fermentation of wine via Saccharomyces
First stage of wine fermentation - defines the wines alcohol content
Sugar –> Ethanol + CO2
* Fermentation is inhibited when ethanol reaches about 15%
* Amount of starting sugar determines sweetness of wine
Secondary fermentation of wine (malolactic fermentation)
Is this done by a diff bacteria?
Malic acid –> lactic acid + CO2
via Oenococcus oeni (lactic acid bacteria)
* contributes to the flavor of the wine and the “buttery” mouthfeel
Was beer invented or discovered
Discovered
- Mesopotamia 4000 BC
Production of traditionally fermented foods typically
relies on ____ microbiota, whereas commercial
fermentation generally relies on ________.
a) soil; edible
b) edible; indigenous
c) airborne; indigenous
d) indigenous; starter cultures
e) indigenous; chemicals
d) indigenous; starter cultures
3 “special” microbes used to make “sour beer”
- Brettanomyces (instead of Sacc.)
- Lactobacillus
- Pediococcus
Acetic acid and lactic acid
fermentation in addition to alcoholic
fermentation
How is cheese made through fermentation (primary)
Primary fermentation with lactic acid bacteria
* lactose -> lactic acid: milk protein (Casein) insolube in the acidic environment and curdles = curds and liquid whey
* Curds = cheese
Proteolytic enzyme (used in cheese making) that helps coagulate milk more efficiently and completely than acid alone
Rennet
* enzyme from 4th stomach of a calf
