Molds Flashcards
What is a mycotoxin
A fungal metabolite that when ingestion, inhaled or absorbed, cause disease
Mycotoxin production occurs only as a result of…
Fungal growth (not the presence of spores)
Toxicity due to mycotoxins is…
Cumulative of a long period of time
5 mycotoxins discussed in class
Aflatoxins, ochratoxin A, fumonisins, deoxynivalenol, zearalenone
Symptoms of aflatoxicosis
Jaundice, fever, vomiting and anorexia
4 naturally occurring aflatoxins
B1, B2, G1, G2
How are aflatoxins named
Based on their fluorescence under UV light
What happens when aflatoxins are eaten by lactating cows
They are excreted as aflatoxins M1 and M2
What are two organisms that produce aflatoxins important in food
Aspergillus flavus and parasiticus
What is the growth temp and Aw of A. flavus
T: 10-48C
Aw: depends on temp (decreases with increasing temp)
How can A. flavus be destroyed
Pasteurization
Where is A. flavus found
Common in food crops in tropical and warm areas (peanuts, corn, tree nuts)
Where is A. parasiticus found
More associated with peanuts (more geographically limited than A. flavus)
What is a prereq for high aflatoxin levels in peanuts
Aspergillus infection while the nuts are still in the ground
What contributes to pre-harvest Aspergillus infection in peanuts
High spore numbers, drought, high soil temp
Control strategies for Aspergillus
Crop rotation, irrigation, biocontrol (inoculating fields with non-toxic strains so they compete with each other)
3 methods for removal of aflatoxin by heat and their effectiveness
- Boiling/autoclaving - less than 25%
- Dry roasting - up to 80%
- Alkali process (peanut oil) - 100%
5 primary toxic effects of aflatoxin
Acute toxicity, liver carcinogenicity, liver cirrhosis, immunosuppression, growth retardation in children
What is the relation between hepatitis B and aflatoxin
If you have hep B, you are 30 times more likely to develop liver cancer
How does aflatoxin cause liver cancer
NEED to have consumption of low levels over long period of time
- Liver enzymes convert aflatoxin to epoxide
- Epoxide binds liver proteins and causes liver failure
- Epoxide binds DNA and is precursor for liver cancer
What part of the immune system does aflatoxins suppress
Cell-mediated immune response
3 effects of immunosuppression by aflatoxin
- Decrease phagocytic activity of macrophages
- Increased susceptibility to infection
- Reduced response to vaccines
What is the acceptable safe level of consumption of aflatoxin in humans
15ug/kg
What 3 groups of fungi produce ochratoxin A
- Ocher-color aspergilli
- Black aspergilli
- Penicillium
What does OTA do
Is a nephrotoxin that affects kidney function and has carcinogenic properties
How can you tell if someone has ingest OTA
Blood test, it has a long half life (3 weeks) in the blood
What is the mechanism of OTA
Unclear, likely related to phenylalanine metabolism
What are people in NA exposed to OTA from (fungi and products)
Penicillium verrucosum
Products include barely, wheat, coffee, wine, beer
Where are OTA levels low
Tropical and subtropical regions
What is the tolerable weekly intake of OTA
100ng/kg
What control method prevents OTA production
Rapid drying (hard to do)
What is a known fungi that produces OTA in wine
A. carbonarius
4 control methods to prevent A. carbonarius growth in grapes
- Proper irrigation
- Air flow
- Crop covers
- Fungiside applications
What can lead to OTA formation in coffee beans
Slow drying
What can control OTA production in coffee beans
Effective sun drying or mechanical dehydration
What fungi produces fumonisins
Fusarium verticilloides and F. proliferatum
Also A. niger
Where are fusarium species always present
On corn and sorghum
A. niger is associated with fumonisins in…
Grapes, raisins and coffee
What is a concern of A. niger producing fumonisins
It can also produce OTA, and the co-occurrence of the two would be bad
How do Fusarium colonized kernels start showing mycotoxin symptoms
When the plant is stressed (drought, heat of insect predation), it leads to a disease-mycotoxin producing interaction
What do fumonisins do
They affect sphingolipid metabolism, cause depletion of complex sphingolipids and this interferes with the function of some membrane proteins (inhibition of folate binding)
What does fumonisins cause in humans
Esophageal cancer and neural tube defects, like spina bifida in infants
How can you prevent fungal growth in corn
Rapid drying (cannot live below Aw 0.9)
What is mixtamalization
A process where the corn is soaked and cooked in an alkaline solution to remove almost fumonisins
If a product is processed above __, fumonisins levels are decrease
150C
What fungi produce deoxynivalenol (DON)
Fusarium graminearum (some) Fusarium culmorum (all)
Where is F. culmorum found
Small grains (wheat and barely)
What is the action of DON
Inhibits protein synthesis
Where is DON production on corn the highest
Cooler, wet climate (like canada)
What is a safe level of consumption of DON in human and bovine feeds
Human: 1mg/kg
Bovine: 10mg/kg
What are some control methods for DON
Fungicides, crop rotation, forecasting symptoms (to warn producers)
What activity does zearalenone have in pigs, cattle and sheep
Estrogenic activity
What are symptoms of ZEA in pigs
Vulvovaginitis and vaginal rectal prolapse
What fungi produce ZEA
Same fusarium species that produce DON, F. graminearum and F. culmorum (generally under same conditions)
4 toxic effects of ZEA
Hepatotoxic, hematotoxic, immunotoxic, genotoxic
What are the 3 mold genera most commonly associated with food
Aspergillus, penicillum and fusarium
