microbial spoilage and public health concerns part 2

Question 1

milk is a great growth media for bacteria because of its ____, _____, and _____

Answer 1

high water content,
near-neutral pH,
available nutrients

Question 2

why do we pasteurize milk?

Answer 2

to eliminate pathogens and increase shelf life

Question 3

at what temperature does milk lipolysis happen faster?

Answer 3

4C

Question 4

at what temperature does milk proteolysis happen fastest?

Answer 4

7C

Question 5

____ are the main source of nitrogen for bacterial growth

Answer 5

casein proteins

Question 6

what carbon is the most common carbon source in milk?

Answer 6

lactose, but glucose is also present in milk and serves to allow some growth of microbes

Question 7

what non-protein nitrogen in milk is also readily available for microbial metabolism?

Answer 7

urea, peptides, and amino acids

Question 8

what are the two major inhibitors of microbial growth in milk?

Answer 8

lactoferrin and lactoperoxidase

Question 9

why is lactoferrin an inhibitor of microbial growth?

Answer 9

lactoferrin binds iron which makes iron a limiting factor for bacterial growth in milk

Question 10

why is lactoperoxidase an inhibitor of microbial growth?

Answer 10

survives pasteurization. catalyzes oxidation of thiocyanate when H202 and in the process creates hypothiocyanite which is a highly reactive oxidant and is antimicrobial

Question 11

what other inhibitors are there of milk?

Answer 11

lysozyme, specific immunoglobins, and folate and vitamin B12 binding systems

Question 12

what is the limiting substrate in the lactoperoxidase system?

Answer 12

hydrogen peroxide

adding a hydrogen peroxide generation system to the milk increases effectiveness of the lactoperoxidase system

Question 13

what two things does the preservation of milk rely on?

Answer 13

effective sanitation (pasteurization) and refrigeration

Question 14

what is the process of pasteurizing and refrigerating milk?

Answer 14

raw milk is kept cold until pasteurization after which it is kept cold again until consumption

Question 15

what kind of bacteria are generally the ones responsible for spoiling both raw and pasteurized milk?

Answer 15

psychotrophic aerobic gram-negative rods

Question 16

65-70% bacteria isolated from raw milk will be ______ spp.

Answer 16

Pseudomonas

Question 17

what other psychrotrophic bacteria are present in milk?

Answer 17

Aeromonas, bacillus, listeria, staphylococcus, and Enterococcus

Question 18

does psychrotrophic milk spoilage rely more on proteolysis or lipolysis to spoil the milk?

Answer 18

proteolysis

Question 19

what bacteria are most associated with milk spoilage?

Answer 19

pseudomonas

Question 20

____ are unable to ferment lactose

Answer 20

pseudomonas sp.

Question 21

where does pasteurized milk become contaminated?

Answer 21

in milk processing plant equipment and air

Question 22

what causes milk spoilage by LAB?

Answer 22

when the milk temperature is abuse, and is stored at temperatures sufficiently high for gram-positive acid-producers to outgrow psychrotrophic

Question 23

what is the effect of “wild” LAB milk spoilage?

Answer 23

producing unwanted gas or off flavors due to the production of acetic acid and propionic acids

Question 24

why do dairy products spoil differently than milk products?

Answer 24

other dairy products provide different environments, the pH has been altered, and the water activity differs

Question 25

why is hard to determine how spoilage occurs in fruits and vegetables?

Answer 25

a single produce item could be cultivated under several different conditions under many different climates.

Question 26

____ correlates negatively with the shelf-life of fruits and vegetables. what does this mean exactly?

Answer 26

respiration rate. products with a high respiration rate have a short shelf life, products with a low respiration rate have a long shelf life.

Question 27

what compound increases produce maturity?

Answer 27

ethylene

Question 28

what does the aging process in fruits and vegetables lead to?

Answer 28

irreversible changes in the structure of fruit and vegetables, leading to deterioration

Question 29

Respiration also leads to ___ leading to ___ and wilting.

Answer 29

moisture loss | structural damage

Question 30

what is the significance of the cuticle barrier in spoilage of fruit and vegetable?

Answer 30

the cuticle barrier can be compromised by several spoilage bacteria by various enzymatic processes

Question 31

what is an appressorium?

Answer 31

a structure formed at the end of spoilage fungi's germ tubes, which serves to attach and penetrate plant surfaces by mechanical pressure, initiating fungal spoilage

Question 32

What is the water content of fruits and vegetables?

Answer 32

>95%, and contain a significant amount of nutrients essential for microbial growth

Question 33

spoilage of low pH fruits is caused by _____ and _____, which are more tolerant to high _____.

Answer 33

yeasts, molds, high acidity

Question 34

what antimicrobial compounds do fruits and vegetables contain?

Answer 34

tannins and phenolic compounds, sulfur-derived antimicrobials (onions or garlic), or terpenoids in carrots

Question 35

what are phytoalexins?

Answer 35

small molecules produced by plants in response to PAMPs on bacteria

Question 36

what are phytoanticipins

Answer 36

pre-existing phytoalexins that interact with a plant pathogen

Question 37

_____ may be involved in plant resistance

Answer 37

phytoanticipins

Question 38

what factors contribute to reducing respiratory activity in fruits and vegetables?

Answer 38

control of temperature, relative humidity, and composition of the gaseous atmosphere

Question 39

what storage temperature is recommended for fruits and vegetables?

Answer 39

0C

Question 40

what produce should not be stored at 0 Celcius due to chilling injuries

Answer 40

produce from tropical regions

Question 41

what relative humidity is recommended for most fruits and vegetables?

Answer 41

90%, except for garlic and onions

Question 42

what is the edible portion of the nut called?

Answer 42

seed, kernel, or meat

Question 43

how are nuts preserved?

Answer 43

lowering the water activity to below 0.7- prevents bacteria growth and increases shelf life

Question 44

what kind of nuts are peanuts?

Answer 44

ground nuts as opposed to a tree nut

Question 45

what is the significance of aspergillus flavus

Answer 45

a ubiquitous invader, and produces a mycotoxin is a major issue

Question 46

when does microbiological contamination occur in cereal grains?

Answer 46

while the grains are growing, and during and after harvest

Question 47

what limits the growth of microbes?

Answer 47

drying the grains and good storage practices

Question 48

what are the most common contaminants of grains?

Answer 48

molds

Question 49

what are field fungi?

Answer 49

molds that infect the grain before harvest

Question 50

what are storage fungi?

Answer 50

molds that infect grain after harvest

Question 51

what bacteria are considered field fungi?

Answer 51

Alternaria, Cladoporium, Fusarium, and Helminthosporium

Question 52

what bacteria are considered storage fungi?

Answer 52

Aspergillus, Rhizopus, Mucor, Wallemia, and Penicillium

Question 53

what can improperly dried grains lead to?

Answer 53

high mycotoxin levels

Question 54

what are some advantages to baking?

Answer 54

kills mold spores and vegetative microbial cells

Question 55

what is the predominant cause of baked product spoilage?

Answer 55

mold

Question 56

what happens to the surfaces of baked products while they are cooling and being packaged?

Answer 56

surfaces are re-contaminated with airborne mold spores

Question 57

most commercial bakery products contain one or more ____ agents to retard mold growth

Answer 57

fungistatic

Question 58

bakery products with a ____ interior are prone to rope-spoilage

Answer 58

moist interior

Question 59

what is rope spoilage due to

Answer 59

extracellular capsid material produced by bacillus subtilis