Food microbiology Flashcards
Physical characteristics of lactic acid bacteria
Gram-positive, aerotolerant anaerobes
Rods or cocci
What are homofermentative
Fermentation yields primarily lactic acid ( pickles, sauerkraut)
What is heterofermentative
Fermentation yilds lactic acid and a variety of flavorful compounds (fermented sausages such as salami, fermented milk products)1
what does lactic acid do to food
Reduces food spoilage and improves storage qualities ( brings the pH down)
what strains of yeast are used for alcoholic beverages production
Variety of Saccharomyces strains
What is sauerkraut
Cabbage is simply shredded and salted
What is the final salt concentration of salt in sauerkraut
2.2-2.8%
Microorganisms naturally present on cabbage
Leuconostoc mesenteroides
Lactobacillus plantarum
what is the difference between Leuconostoc mesenteroides
AND
Lactobacillus plantarum
Leuconostoc mesenteroides produces lactic acid and flavor compounds and it is killed when acidity reaches 0.7-1%
Lactobacillus plantarum produces lactic acid only, increases acidity to 1.6-1.8%
What cultures are used for pickles
- Natural
- Or sometimes the natural one is killed and use of pure culture of Pediococcus cerevisiae and Lactobacillus plantarum
pure culture of Pediococcus cerevisiae and Lactobacillus plantarum is also used for
Production of fermented sausages, salami, bologna
Salami: ingredients
Made with ground pork and/or beef
Mixed with other ingredients: salt, sugar, spices, yeast. Sometimes a starter lactic acid bacterial culture is added
How the salami is made after addition of all ingredients and how the preservation is made
Mixture is added to casing and allowed to cure
The preservation of food by the addition of salt and drying
What are the temperature and humid conditions for salami
Warm (25C), humid (95%) conditions for 1-3 days
Transfer to cool ( 12-18) and humid (70-80%) conditions and dry sausage for 6-10 weeks
Milk naturally contains ____, but it is usually removed by ___.
Lactic acid bacteria
Removed by pasteurization
To make yogurt what cultures are added and at what temperature
Streptococcus thermophilus and Lactobacillus bulgaris incubated at 42C
Other microorganisms are sometimes added ( BL, Bifidobacterium animalis)
What is happening in the yogurt with microorganisms
Streptococci produce some acids and favor the growth of Lactobacillus which produce most of the acid
The acid denatures casein which results in thickening
Two basic steps in cheese making
Curdling: lactic acid bacteria precipitate the proteins -> curd
Ripening: lactic acid bacteria+ other microorganisms -> flavor
Cheese production scheme
Raw milk->pasteurize->filtration-> inoculate organisms ->curdling-> remove the whey and mill the curd->addition of salt/herbs->addition of microorganisms if rippening
What is happening at cheese curdling step
Starter cultures of lactic acid bacteria are added to milk
- Microorganisms ferment lactose, produce lactic acid
- Promote development of the curd (precipitated proteins, fat and other suspended material) and whey (supernatant)
What is the function of rennin
Cleaves casein which results in curd formation ( rennin or lactic acid work)
In the end of curddling step what is done to the mixture
Whey is drained off: starting material for other processes (whey powder), or discarded (high BOD, must be treated like sewage)
After curd has been separated what happens
Curd is then heated: more whey expelled and the curd becomes more solid
Salt may be added: flavor, promotes extraction of water, inhibits growth of spoilage organisms
After salt is added what happens to the curd
Packaging (fresh cheese) , or other processes : pressing, brining, ripening
Ripening of the cheese leads to changes in
Texture, consistency, flavor
Some of the ripening is due to
The lactic acid bacteria, rennin or other enzymes present
Cheddar, swiss cheese and gouda are riped in
cheesecloth
Cheddar: ripening involves only
The lactic acid bacteria
Longer the ripening of cheddar, swiss and gouda, then
higher acidity and sharpness
WHat happens in swiss cheese during ripening
Propioibacteria produce propionic acid and acetic acid (flavor) and CO2 (bubbles)
cheddar, swiss and gouda are riped for
3-12 months
Oka is (bacteria, what is done to the cheese)
pressed curd is brined, surface washed frequently. Growth of Geotrichum
In blue cheese and ruquefort ripening happens mainly due to
The mold Penicillium roquefortii
How the blue cheese has its blue color
Spores from the mold are mixed with milk or the curd
Small holes are drilled in the curd before wrapping
The mold grows in the holes and produces spores (blue)
For how long blue cheese and roquefort are ripened
3-6 months
Camembert is stored wrapped/unwrapped
Unwrapped
What bacteria are spread on the surface in the curd on camembert and brie
Mixture of mold(Penicillium) and bacteria (Brevibacterium)
Where the ripening of camembert and brie happens and for how long
Ripening in curing room (high humidity)
1-5 months
What is responsible for softening of the cheese in camembert and brie
Proteases
What is the precaution for camembert and brie
Good sanitary practices are required so that the cheese does not get contaminated
What is the must
Crushed grains of grapes
What is the purpose of metabisulfite (Na2S2O5)
to kill wild yeasts
What can be added to the must
sugar and organic acids depending on the final product