Lecture 15 Flashcards
Intrinsic factors
factors related to food itself (carbs, proteins, lipids)
extrinsic factors
Environment where food stored
Intrinsic factors (carbs)
carb rich food show spoilage by fungi
Enzymes degrade food by hydrolysis, once mold degrades outer layer bacteria can colonize, toxins may be produced
Intrinsic factors (proteins/fats)
Bacterial growth predominates,
putrefaction - proteolysis and anaerobic breakdown of proteins (smell)
Unpasteurized milk - acid production, bacteria, proteins and fat coagulate (clear)
Other intrinsic factors
pH - low pH = mold, yeast neutral = bacteria
Presence/availability of water - lower water activity inhibits growth
Physical structure - grinding/ mixing distributes microbe
Antimicrobial food substances
Coumarins, lysozyme, aldehydic and phenolic compounds, allicin, eugenol, polyphenols, rosmarinic acid
Extrinsic factors
Temp, relative humidity = higher levels = growth, atmosphere = oxygen promotes growth
Temperature (microbial growth)
low temp - 5 degrees slows but doesn’t stop growth
High temp - kills spoilage microbes not all
Pasteurization (LTH, HTST, HTLT, UHT)
kills pathogens and reduces number of spoilage organisms, different heat for different things
LTH - low temp holding = beer, fruit juice, milk for yogurt
HTST = High short time, milk
HTLT = high, long, fruit juice milk
UHT = ultra high = milk with no fridge
GRAS
chemical agents = generally recognized as safe,
Bacteriocins
Proteins active against related species, dissipate pmf of susceptible bacteria, form pores in plas mem, inhibit protein synthesis
Food borne infection
ingestion of pathogen, followed by growth and tissue invasion/release of toxins (raw food)
Listeriosis
-pregnant women, young and old, immunocompromised most vulnerable
Responsible for largest meat recall in US
Food borne intoxications
ingestion of toxins in foods in which microbes have grown, produce symptoms shortly after
Botulism (caused by)
caused by clostridium botulinum, gram +, anaerobic, neurotoxin, affects cranial nerves,
food from canned goods not properly preserved, exposure to open wounds
Fermented milks
lactic acid bacteria, lactobaccilus, lactococcus, gram +, acid tolerant
Cheese production
lactic acid fermentation
milk > lactic acid bacteria > curd > removal of whey > ripening > cheese
Wines and champagnes
enology (wine) = crushed grapes, treated with sulfer dioxide, yeast added, malolactic fermentation
Sweet wines = fermentation stopped early
Champagne = fermentation continues, add sugar
Beer Brewing
Cereal grains used for fermentation
malt = dry, sprouted barley grains
Mash = malt after being mixed with hot water
Wort = liquid extracted from mashing
Wort heated, hops added = heating stops enzymes, kills microbes, hops are for flavor
Lagers and ales
cooled wort inoculated with desired yeast, fermentation produces alcohol and CO2
Foods modified by fermentations
meats, coffee, soy sauce, sauerkraut, pickles, silage
Discovery of CRISPR- Cas
sequencing streptococcus thermophilius genome, realized that repeat regions have viral sequences, cas proteins cut DNA, tracr sequences identified, realized it could edit genomes
Restriction modification system
restriction enzymes cleave and destroy foreign DNA, own sequences guarded by methylation
CRISPR Cas (stand for)
clustered regularly interspaced short palindromic repeats
-repeating sequences of DNA in bacteria separated by spacer sequences
Crispr associated (Cas)
-nuclease use spacer as guide
2 stage CRISPR
- adaptation stage = addition of DNA sequence to end region following survived infections
- Interference stage = 2nd time with virus, crispr locus transcribed and processed into crispr RNA molecules, cas bind to viral DNA = destruction
Cas enzymes (2)
- Class 1 = multi-subunit crRNA-effector complexes
- Class 2 = single subunit nuclease, multiple domains, best for genome editing
CRISPR components
CAS 9 - protein nuclease
crRNA - spacer DNA transcribed into crRNA
Tracr- trans-activating crRNA
PAM - Protospacer adjacent motif sequence must also be present near target sequence
Cas 9 cleavage of DNA
RNA guided, crRNA + Tracr RNA required, combined into 1, pam sequence must be adjacent to target, cas 9 assembles at target and cuts DNA strands = blunt ends, DNA break repaired or lethal to cell
Double stranded break outcomes
- non homologous end joining system repairs break, can accidentally introduce point mutations
- piece of double stranded DNA can be added, donor DNA integrated into genome by homologus recombination
Cas 9 protein structure
REC I: binding of guide RNA, PAM interacting: recognize PAM sequence
HNH: nuclease
RuvC: nuclease
Nuclease domains can be deactivated by mutation
Applications of Crispr
gene activation, epigenome modification, base editing, chromatin imaging
