13 - Microbial Spoilage and Public Health Concerns pt 2

Question 1

several milk spoilage bacteria can rely on what processes for energy generation?

Answer 1

proteolysis and lipolysis

Question 2

lipolysis is favorable under what conditions?

Answer 2

at 4C. bc psychrotrophic bacteria have a faster growth rate here and produce lipases.

Question 3

proteolysis is favorable under what conditions?

Answer 3

7C

Question 4

what is the more common carbon source for bacterial spoilage in milk?

Answer 4

lactose

Question 5

what are the main source of nitrogen in milk?

Answer 5

casein

Question 6

what are non-protein nitrogen sources in milk?

Answer 6

• urea
• peptides
• amino acids

Question 7

what are the major inhibitors of microbial growth in milk?

Answer 7

lactoferrin and lactoperoxidase

Question 8

what does lactoferrin do?

Answer 8

binds iron, making it a limiting factor.

Question 9

why isn’t lactoferrin as effective in cow’s milk as it is in human’s?

Answer 9

cow’s milk has more citrate which binds lactoferrin

Question 10

what does lactoperoxidase do?

Answer 10

catalyzes the oxidation of thiocyanate and produces hypothiocyanite, a highly reactive oxidant

Question 11

what are some of the less major natural inhibitors in milk?

Answer 11

lysozyme, specific immunoglobulins, folate, and vit B12

Question 12

what is the limiting substrate in the lactoperoxidase system?

Answer 12

H2O2

Question 13

adding H2O2 to milk will (increase/decrease) effectiveness of the lactoperoxidase system

Answer 13

increase

Question 14

what microorgs are inhibited by the lactoperoxidase system?

Answer 14

LAB, coliforms, several pathogenic bacteria

Question 15

true or false: it’s important to refrigerate raw milk before it’s pasteurized

Answer 15

true

Question 16

what is the predominant bacteria in raw milk?

Answer 16

Pseudomonas sp.

Question 17

what kind of respiratory bacteria will dominate spoiled refrigerated milk?

Answer 17

obligate aerobes

Question 18

describe what happens to bacteria numbers over time during milk spoilage

Answer 18

• enterobacteriaceae increase but are eventually overtaken by Pseudomonadaceae
• if there’s spores, it’s usually from Bacillus genus

Question 19

what does psychrotrophic milk spoilage rely on?

Answer 19

proteolysis. lipolysis to a lesser extent

Question 20

what is the bacteria most associated with milk spoilage?

Answer 20

Pseudomonas sp.

Question 21

can Pseudomonas sp. ferment lactose?

Answer 21

no

Question 22

what causes bitter and putrid flavors in milk?

Answer 22

proteolysis

Question 23

what causes rancid and fruit flavors in milk?

Answer 23

lipolysis

Question 24

what do wild LAB do to spoil milk?

Answer 24

produce unwanted gas or off-flavors due to production of other organic acids (acetic and propionic)

Question 25

what factors make dairy products spoil differently from milk?

Answer 25

- nutrient composition - pH - water activity

Question 26

products with a (high/low) respiration rate can be stored for a long time

Answer 26

low

Question 27

what does ethylene do?

Answer 27

increases maturity

Question 28

what causes moisture loss?

Answer 28

respiration

Question 29

what is an appressorium?

Answer 29

structure at the end of a fungus' germ tubes used to attach and penetrate plant surfaces by mechanical pressure

Question 30

how can pathogens enter plant material?

Answer 30

- wounds | - natural openings

Question 31

fruits and vegetable have a (high/intermediate/low) water content

Answer 31

high

Question 32

what is the main limitation preventing growth of bacteria in fruits & veg?

Answer 32

pH

Question 33

what causes spoilage in low pH fruits & veg?

Answer 33

molds and yeasts

Question 34

what are some antimicrobial compounds found in plants?

Answer 34

- tannins - phenolic compounds - sulfur-derived antimicrobials - terpenoids - phytoanticipins - phytoalexins

Question 35

storage close to what temperature is recommended for most fruits and veggies?

Answer 35

0C

Question 36

a RH of ____ is recommended for most fruits and veggies

Answer 36

90%

Question 37

what is the edible portion of a nut called?

Answer 37

seed, kernel, meat

Question 38

how are nuts preserved?

Answer 38

lowering aw below 0.7

Question 39

most nut spoilage is caused by _____

Answer 39

oxidation of nut fats

Question 40

what is the major spoilage organism associated w/peanuts?

Answer 40

Aspergillus flavus (the aflatoxin guy)

Question 41

when does microbial contamination of cereal grains happen?

Answer 41

when grains are growing

Question 42

what are the most common contaminants of cereals?

Answer 42

molds

Question 43

what are field fungi?

Answer 43

infect grain before harvest

Question 44

what are storage fungi?

Answer 44

infect grain after harvest

Question 45

list some field fungi

Answer 45

- Alternaria - Cladosporium - Fusarium - Helminthosporium

Question 46

list some storage fungi

Answer 46

- Aspergillus - Rhizopus - Mucor - Wallemia - Pennicillium

Question 47

does baking kill mold spores?

Answer 47

yes

Question 48

what is the main culprit of spoilage of baked products?

Answer 48

mold

Question 49

what kind of agents are added to bakery products to retard mold growth?

Answer 49

fungistatic

Question 50

bakery products with a moist interior are prone to _____ spoilage due to the bacteria called _____ _____

Answer 50

rope; Bacillus subtilis