microbial spoilage and public health concerns part 2 Flashcards
milk is a great growth media for bacteria because of its ____, _____, and _____
high water content,
near-neutral pH,
available nutrients
why do we pasteurize milk?
to eliminate pathogens and increase shelf life
at what temperature does milk lipolysis happen faster?
4C
at what temperature does milk proteolysis happen fastest?
7C
____ are the main source of nitrogen for bacterial growth
casein proteins
what carbon is the most common carbon source in milk?
lactose, but glucose is also present in milk and serves to allow some growth of microbes
what non-protein nitrogen in milk is also readily available for microbial metabolism?
urea, peptides, and amino acids
what are the two major inhibitors of microbial growth in milk?
lactoferrin and lactoperoxidase
why is lactoferrin an inhibitor of microbial growth?
lactoferrin binds iron which makes iron a limiting factor for bacterial growth in milk
why is lactoperoxidase an inhibitor of microbial growth?
survives pasteurization. catalyzes oxidation of thiocyanate when H202 and in the process creates hypothiocyanite which is a highly reactive oxidant and is antimicrobial
what other inhibitors are there of milk?
lysozyme, specific immunoglobins, and folate and vitamin B12 binding systems
what is the limiting substrate in the lactoperoxidase system?
hydrogen peroxide
adding a hydrogen peroxide generation system to the milk increases effectiveness of the lactoperoxidase system
what two things does the preservation of milk rely on?
effective sanitation (pasteurization) and refrigeration
what is the process of pasteurizing and refrigerating milk?
raw milk is kept cold until pasteurization after which it is kept cold again until consumption
what kind of bacteria are generally the ones responsible for spoiling both raw and pasteurized milk?
psychotrophic aerobic gram-negative rods
65-70% bacteria isolated from raw milk will be ______ spp.
Pseudomonas
what other psychrotrophic bacteria are present in milk?
Aeromonas, bacillus, listeria, staphylococcus, and Enterococcus
does psychrotrophic milk spoilage rely more on proteolysis or lipolysis to spoil the milk?
proteolysis
what bacteria are most associated with milk spoilage?
pseudomonas
____ are unable to ferment lactose
pseudomonas sp.
where does pasteurized milk become contaminated?
in milk processing plant equipment and air
what causes milk spoilage by LAB?
when the milk temperature is abuse, and is stored at temperatures sufficiently high for gram-positive acid-producers to outgrow psychrotrophic
what is the effect of “wild” LAB milk spoilage?
producing unwanted gas or off flavors due to the production of acetic acid and propionic acids
why do dairy products spoil differently than milk products?
other dairy products provide different environments, the pH has been altered, and the water activity differs
why is hard to determine how spoilage occurs in fruits and vegetables?
a single produce item could be cultivated under several different conditions under many different climates.
____ correlates negatively with the shelf-life of fruits and vegetables. what does this mean exactly?
respiration rate.
products with a high respiration rate have a short shelf life, products with a low respiration rate have a long shelf life.
what compound increases produce maturity?
ethylene
what does the aging process in fruits and vegetables lead to?
irreversible changes in the structure of fruit and vegetables, leading to deterioration
Respiration also leads to ___ leading to ___ and wilting.
moisture loss
structural damage
what is the significance of the cuticle barrier in spoilage of fruit and vegetable?
the cuticle barrier can be compromised by several spoilage bacteria by various enzymatic processes
what is an appressorium?
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
What is the water content of fruits and vegetables?
> 95%, and contain a significant amount of nutrients essential for microbial growth
spoilage of low pH fruits is caused by _____ and _____, which are more tolerant to high _____.
yeasts,
molds,
high acidity
what antimicrobial compounds do fruits and vegetables contain?
tannins and phenolic compounds, sulfur-derived antimicrobials (onions or garlic), or terpenoids in carrots
what are phytoalexins?
small molecules produced by plants in response to PAMPs on bacteria
what are phytoanticipins
pre-existing phytoalexins that interact with a plant pathogen
_____ may be involved in plant resistance
phytoanticipins
what factors contribute to reducing respiratory activity in fruits and vegetables?
control of temperature, relative humidity, and composition of the gaseous atmosphere
what storage temperature is recommended for fruits and vegetables?
0C
what produce should not be stored at 0 Celcius due to chilling injuries
produce from tropical regions
what relative humidity is recommended for most fruits and vegetables?
90%, except for garlic and onions
what is the edible portion of the nut called?
seed, kernel, or meat
how are nuts preserved?
lowering the water activity to below 0.7- prevents bacteria growth and increases shelf life
what kind of nuts are peanuts?
ground nuts as opposed to a tree nut
what is the significance of aspergillus flavus
a ubiquitous invader, and produces a mycotoxin is a major issue
when does microbiological contamination occur in cereal grains?
while the grains are growing, and during and after harvest
what limits the growth of microbes?
drying the grains and good storage practices
what are the most common contaminants of grains?
molds
what are field fungi?
molds that infect the grain before harvest
what are storage fungi?
molds that infect grain after harvest
what bacteria are considered field fungi?
Alternaria, Cladoporium, Fusarium, and Helminthosporium
what bacteria are considered storage fungi?
Aspergillus, Rhizopus, Mucor, Wallemia, and Penicillium
what can improperly dried grains lead to?
high mycotoxin levels
what are some advantages to baking?
kills mold spores and vegetative microbial cells
what is the predominant cause of baked product spoilage?
mold
what happens to the surfaces of baked products while they are cooling and being packaged?
surfaces are re-contaminated with airborne mold spores
most commercial bakery products contain one or more ____ agents to retard mold growth
fungistatic
bakery products with a ____ interior are prone to rope-spoilage
moist interior
what is rope spoilage due to
extracellular capsid material produced by bacillus subtilis
