Lecture 15

Question 1

Intrinsic factors

Answer 1

factors related to food itself (carbs, proteins, lipids)

Question 2

extrinsic factors

Answer 2

Environment where food stored

Question 3

Intrinsic factors (carbs)

Answer 3

carb rich food show spoilage by fungi
Enzymes degrade food by hydrolysis, once mold degrades outer layer bacteria can colonize, toxins may be produced

Question 4

Intrinsic factors (proteins/fats)

Answer 4

Bacterial growth predominates,
putrefaction - proteolysis and anaerobic breakdown of proteins (smell)
Unpasteurized milk - acid production, bacteria, proteins and fat coagulate (clear)

Question 5

Other intrinsic factors

Answer 5

pH - low pH = mold, yeast neutral = bacteria
Presence/availability of water - lower water activity inhibits growth
Physical structure - grinding/ mixing distributes microbe

Question 6

Antimicrobial food substances

Answer 6

Coumarins, lysozyme, aldehydic and phenolic compounds, allicin, eugenol, polyphenols, rosmarinic acid

Question 7

Extrinsic factors

Answer 7

Temp, relative humidity = higher levels = growth, atmosphere = oxygen promotes growth

Question 8

Temperature (microbial growth)

Answer 8

low temp - 5 degrees slows but doesn’t stop growth
High temp - kills spoilage microbes not all

Question 9

Pasteurization (LTH, HTST, HTLT, UHT)

Answer 9

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

Question 10

GRAS

Answer 10

chemical agents = generally recognized as safe,

Question 11

Bacteriocins

Answer 11

Proteins active against related species, dissipate pmf of susceptible bacteria, form pores in plas mem, inhibit protein synthesis

Question 12

Food borne infection

Answer 12

ingestion of pathogen, followed by growth and tissue invasion/release of toxins (raw food)

Question 13

Listeriosis

Answer 13

-pregnant women, young and old, immunocompromised most vulnerable
Responsible for largest meat recall in US

Question 14

Food borne intoxications

Answer 14

ingestion of toxins in foods in which microbes have grown, produce symptoms shortly after

Question 15

Botulism (caused by)

Answer 15

caused by clostridium botulinum, gram +, anaerobic, neurotoxin, affects cranial nerves,
food from canned goods not properly preserved, exposure to open wounds

Question 16

Fermented milks

Answer 16

lactic acid bacteria, lactobaccilus, lactococcus, gram +, acid tolerant

Question 17

Cheese production

Answer 17

lactic acid fermentation
milk > lactic acid bacteria > curd > removal of whey > ripening > cheese

Question 18

Wines and champagnes

Answer 18

enology (wine) = crushed grapes, treated with sulfer dioxide, yeast added, malolactic fermentation
Sweet wines = fermentation stopped early
Champagne = fermentation continues, add sugar

Question 19

Beer Brewing

Answer 19

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

Question 20

Lagers and ales

Answer 20

cooled wort inoculated with desired yeast, fermentation produces alcohol and CO2

Question 21

Foods modified by fermentations

Answer 21

meats, coffee, soy sauce, sauerkraut, pickles, silage

Question 22

Discovery of CRISPR- Cas

Answer 22

sequencing streptococcus thermophilius genome, realized that repeat regions have viral sequences, cas proteins cut DNA, tracr sequences identified, realized it could edit genomes

Question 23

Restriction modification system

Answer 23

restriction enzymes cleave and destroy foreign DNA, own sequences guarded by methylation

Question 24

CRISPR Cas (stand for)

Answer 24

clustered regularly interspaced short palindromic repeats
-repeating sequences of DNA in bacteria separated by spacer sequences
Crispr associated (Cas)
-nuclease use spacer as guide

Question 25

2 stage CRISPR

Answer 25

1. adaptation stage = addition of DNA sequence to end region following survived infections
2. Interference stage = 2nd time with virus, crispr locus transcribed and processed into crispr RNA molecules, cas bind to viral DNA = destruction

Question 26

Cas enzymes (2)

Answer 26

1. Class 1 = multi-subunit crRNA-effector complexes
2. Class 2 = single subunit nuclease, multiple domains, best for genome editing

Question 27

CRISPR components

Answer 27

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

Question 28

Cas 9 cleavage of DNA

Answer 28

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

Question 29

Double stranded break outcomes

Answer 29

1. non homologous end joining system repairs break, can accidentally introduce point mutations
2. piece of double stranded DNA can be added, donor DNA integrated into genome by homologus recombination

Question 30

Cas 9 protein structure

Answer 30

REC I: binding of guide RNA, PAM interacting: recognize PAM sequence
HNH: nuclease
RuvC: nuclease
Nuclease domains can be deactivated by mutation

Question 31

Applications of Crispr

Answer 31

gene activation, epigenome modification, base editing, chromatin imaging