Microbiology of food 1 Flashcards
lactic acid bacteria is ?
Gram positive, aerotolerant anaerobe, rods or cocci
Homofermentative
fermentation yields primarily lactic acid (prickles, saukraut)
Heterofermentative
fermentation yields lactivist acid and a variety of flavourful coonhounds ( salami, milk)
benefits of lactic acid?
increases food storage by reducing food spoilage
why pasteurize before fermentation?
kill the natural microbiome of the food item
Cheddar
lactic acid
Swiss
lactic acid + propionibacteria
propionibacter produce propionic acid and acetic acid (flavour) and Co2 (bubbles)
OKA
lactic acid bacteria + Geotrichum
- pressed curd is brined, surface is washed frequently. growth of Geotrichum
Blue, roquefort
ripungi is mainly due to penicillium roquefortii
- spores from the mold are mixed with the milk (or curd)
small holes are drilled in the curd before wrapping - the mold grows in the holes and produces spores
- 3-6 months
Camembert, brie
- unwrapped
picture of Mold (penicillium) and bacteria ( Brevibacterium) - 1-5 months ripening
Proteases secreted by the microorganisms gives it the softness
vinegar
acetic acid bacteria oxidize ethanol to acetic acid- strict aerobes, THIS IS NOT FERMENTATION
ethanol–> acetaldehyde–> acetic acid
Acetobacter: used in all commercial applications
Wine made from
grape must (crushed grapes) + metabisulfite (NA2S2O5) (kills wild yeast)
white wine vs red wine
white= skin removed red= skin kept
dry vs sweet wine
dry= all sugar fermented, sweet= sugar residual
is yeast added to wine?
yes
malting
grains that have been germinated, steeped and dried
production of amylase when grains begin to germinate
mashing
Malth is soaked in warm water. during this time the amylase degrades starch–> fermentable sugars. ( glucose and maltose). Mash is then filtered= WORT
why are hops added?
antimicrobial properties, flavour, bitterness
boiling of wort
wort= filtered mash. gets sterile
S. carlbergensis
botton yeast, for a lager, (14-23)
lager use
S. carbergensis yeast (6-12 degrees)
top yeast=
S. cervisiae, for an ale
for an ale use
s.cervisiae
how to make distilled alcoholic beverages?
malting, mashing, fermentation, distillation, aging and adding flavour
scotch whiskies:
malt brew, wort is not boiled, mixed fermentation of lactic acid and yeast
are lactic acid gram + or neg?
gram +
is lactic acid anaerobic or aerobic?
areotoleraat anaerobe
what shape are lactic acid?
rod or cocci
Salami
mix with salt, sugar , spices and yeast
- sometimes a scatter lactic acid is added
- cure: preservation by addition of salt and drying
yogurt (what is added?)
Streptococcus thermophilic and Lactobacillus bugaris- incubated at 42
Streptococci produce acids which favour the growth of lactobacillus which produces more acid (curdles the milk)
2 methods to make Cheeses
1) starter culture is added to milk
- ferment the lactose, produce lactic acid
- curd develops
2) rennin can be added to culture which cleaves casein and results in curd forming
longer ripening=
higher acidity and sharpness
S. cerevisiae and S.ellipsoideus are resistant to what? and tolerant to what?
NA2S2O5 ( Metabisulfite) and tolerant to 12-14% alcohol
Light beer?
yeasts and geneticaly manipulated so they can use all the sugar in the wort ( no sugar left over)
polishing
filtration, carbonation , pasterization ect
distilling compared to beer making?
hops not added. distil off the water- ethanol vapour is condensed and then collected. aged. different grains used. Vodka= wheat, rye, potatoes Gin= grains Rum: sugar cane Brandy= wine Whiskies= malt brews
what is the scobby in kombucha?
symbiotic culture of bacteria and yeast
- Acetobacter and Saccharomyces
Water activity
availability of water
Xerophiles
dry environment, low osmolarity
Osmophiles
high osmolarity, high sugar
does cold food kill the microorganism
no
most spoilage microorganisms can grow at a AW as low as
0.9
less than ___ most bacteria and yeast cannot grow. can molds grow??
0.9, yes
less than ___ only specialized microogrxs can grow
0.8
hot food kept above?
cold below?
60 degrees
4.5
what do swollen packages indicate?
CO2 production and aerobic microorganisms
natural microorganism in saurqraut
leuconostoc mesenteroides
lactobaccilus plantarum
microorganisms added to yogurt
steptococcus thermophillus
lactobaccillus balgaris
some of the ripening is caused by?
lactic acid, rennin and other enzymes present
which cheese is with lactic acid only
cheddar
longer ripening =
higher acidity and sharpness
propionibacteria is involved in the ripening of
swiss cheese
peniccilum roquforti is involved in the ripening of what cheese?
blue cheese
penicillium and brevibacteria are spread on the surface of what cheese and are involved in ripening?
brie and camambert
