Microbiology Lab Exercise 10: Microbiology of Foods and Beverages

Terms in this set (22)

Fermentation
A type of energy-yielding metabolism in which a carbon source (ex. glucose) is partially oxidized in an anaerobic fashion
Two types of fermentation
Lactic acid fermentation and alcohol fermentation
Organisms that undergo fermentation
Mammals
Bacteria
Fungi
Products of fermentation
A small amount of ATP energy and different organic byproducts
Major organic byproducts produced by fermentation
Ethanol, lactic acid, CO2
Minor organic byproducts produced by fermentation
Carboxylic acids, higher alcohols, aldehydes, ketones
Benefits of fermented foods
Lead to discovery of alcoholic beverages
Keep longer
More versatile in cooking
Enhance flavors of other foods
Lactic acid bacteria
Bacteria that produce lactic acid as a product of fermentation
Streptococcus and Lactobacillus
Fungi involved in fermentation
Saccharomyces (yeast)
Filamentous fungi
Aspergillus and Penicillium
How is wine prepared?
1. A culture of Saccharomyces cerevisiae variety ellipsoideus is added to fruit juice
2. Fermentation lasts 3-5 days at temps from 10C to 13C
3. Juice to be fermented (must) is sometimes pasteurized or disinfected with sulfur dioxide gas before fermentation
4. Wine is aged for a number of years after fermentation
Why is juice to be fermented sometimes pasteurized?
Since fruit contains yeasts and other microorganisms that could interfere with fermentation and produce an inferior product
How is beer prepared?
1. Starts with starchy raw material (generally grain)
2. Some of the starch is converted to sugar to give the yeast a substrate to work on (malting)
3. Grain is placed in warm, humid, environment for a number of days and it sprouts during this time (germination)
4. In germination process, amylase enzymes are induced which convert starch to sugar
5. Once sprouting is complete, grain is dried, roasted, and ground into powder called malt
6. Malt is mixed with water and other grains are added (produces mash)
7. Enzymes from malt break down carbs and proteins in grains
8.Mash is heated, hops added for flavor
9. Cooling, hops removed, yeast is added (Saccharomyces cerevisiae "top yeast" or Saccharomyces carlshergensis "bottom yeast")
10. Fermentation for several days, then pasteurization, filtering, and carbonation
How is cheese prepared?
A process of percipitation
1. Casein (principle protein in milk) is made to come out of the solution to produce curd (the precipitate) and whey (clear, yellowish liquid)
2. Curd is washed, chopped, formed, and processed
Two ways to achieve curd formation
1. Proteinase enzyme called rennin can be used to break certain of the peptide bonds in casein molecule, making it insoluble
2. Acid can also be used
Can be added directly
Lactic acid fermentation: lactose is fermented by bacteria to make lactic acid
Determinants on the type of cheese produced
1. Type of milk used
2. Organisms used, and other details of the fermentation
3. The way the curd is handled after separation
Organisms used to make cheese
Streptococcus lactis
Streptococcus cremoris- Actinomycete group
Brevibacterium linens- Actinomycete group
Penicillium roqueforti (used for bleu cheese)
Homolactic fungi
Fungi that produce lactic acid
Heterolactic fungi
Fungi that produce more than lactic acid
Lactic acid fermentation
Glucose---->Pyruvate----->Lactic Acid
Alcohol fermentation
Glucose---->Pyruvate------>Acetylaldehyde---->Ethanol
Why is it important to eat yogurt when taking antibiotics?
To prevent yeast infections
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