Lab (Post-Midterm)

Question 1

what does SCOBY stand for?

Answer 1

symbiotic culture of bacteria and yeast

Question 2

what agars were used with kombucha?

Answer 2

SD and nutrient agar

Question 3

what does SD agar test for?

is it acidic or basic?

Answer 3

yeast

acidic medium

Question 4

what does nutrient agar test for?

is it acidic or basic?

Answer 4

bacteria

basic medium

Question 5

what are main LAB in kefir?

what are other MOs?

Answer 5

lactobacilli and lactococci

AAB and yeast

Question 6

what media are used in kefir lab?

what does each one test for?

Answer 6

HHD: homo or heterofermentative LAB

MRS: presence of LAB

OGYE: yeast

Question 7

in OGYE, what is the selective agent

Answer 7

oxytetracycline

Question 8

what is the predominant organism of yogurt starter cultures?

Answer 8

LAB

Question 9

what biochemical rxns occur in yogurt fermentation?

Answer 9

CHO –> lactic acid

caseins –> to peptides –> free AA

milk fat –> free FA

Question 10

what agar is used in yogurt lab?

Answer 10

HHD

Question 11

in HHD agar medium, what is the fermentable CHO?

what is the pH indicator?

Answer 11

fructose

bromo cresol green

Question 12

in HHD again, what does heterofermentative LAB producce? what does homo LAB produce?

Answer 12

hetero: Co2, lactic acid, acetic aid, ethanol, mannitol
homo: produces only lactic

Question 13

in yogurt, what color does homofermentative LAB produce?

Answer 13

yellow

due to producing lactic acid from fructose

Question 14

in yogurt, what color does heterofermentative LAB produce?

Answer 14

varies in color depending on medium used

Question 15

on HHD agar, what color does homofermentative LAB produce?

Answer 15

bluish-green colonies

Question 16

on HHD agar, what color does heterofermentative LAB produce?

Answer 16

no color

Question 17

what media were used in maple syrup lab?

Answer 17

nutrient agar

Sabouraud dextrose

Question 18

what does SD agar test for in maple syrup lab?

Answer 18

fungi

Question 19

what kind of maple syrup is more susceptible to fungi growth?

Answer 19

packaged maple syrup not sufficiently heated before sealing

or maple syrup stored for a long time after opening

Question 20

describe the kerby-bauer method in the antibiotics lab

Answer 20

• diskcs with antimicrobial agents are placed on bacterial cultures on Mueller Hinton agar plates
• after incubation, zones of bacterial growth inhibition around the disk are measured and compared with standard zone size

Question 21

what are the two media used in the antibiotics lab

Answer 21

muller hinton

TSA = tryptic soy agar

Question 22

describe the muller hinton agar

Answer 22

• non-selective and non-differential
• many MOs will grow on it
• contains starch (absorbs toxins released from bacteria so they dont interfere with the antibiotics)
• “loose” agar: allows for diffusion of antibiotics through the media to give easier zone inhibition measurements

Question 23

describe TSA

Answer 23

tryptic soy agar

• not selective or differential
• composed of digests of soybean meal and casein
• soy and casein peptones supply N, which makes it highly nutritious
• contains NaCl to maintain osmotic equilibrium

Question 24

in spoilage due to underprocessing of canned food, what MOs will be present?

Answer 24

heat tolerant MOs

Question 25

in spoilage due to can leakage of canned food, what MOs will be present?

Answer 25

hetergeneous

low heat resistance

Question 26

what agars are used in the spoilage food lab?

what does each test for?

Answer 26

tomato serum media: lactobacillus species

nutrient agar: general MOs

plate count agar: bacterial growth

Question 27

what broths are used in the spoilage food lab?

Answer 27

dextrose tryptone broth: MOs which produce acid from dextrose are detected by color change (purple to yellow)

liver broth: to examine saccharolytic or putrefactice mesophilic and thermophilic anaerobes. Bacterial growth produces increase in turbidity and/or gas