Storage Moulds on Grains
Spoilage of grain during storage Degradation of
nutrients Odour Change of grain
properties Contamination
with mycotoxins
Where is the water coming from?
Water availability key! Condensation and moisture content: 17%-18% critical Risk of ‘wet pockets’ or ‘hot
spots’ Fall scenario Spring scenario
Impurities: carry over, dockage, weeds, damaged kernels
Autumn
Spring
PAMI – Facts about Grain Aeration
http://pami.ca/wp-content/uploads/2013/09/Grain-Aeration-Factsheet.pdf
Storage Moulds on Grains
Agar plating of kernels Identification of
toxigenic species Key groups or
genera often identified: Aspergillus Penicillium
Penetration of wheat kernels
Mycelia and conidiophores underneath the bran
Mycelia on cell walls of endosperm
Penicillium verrucosum
Main producer of ochratoxins in cooler climates Occasionally recovered
from cereal grains Ubiquitous, widely
distributed Carry over of inoculum Slow growing
Identification of OTA producing moulds
Selective culture media e.g. dichloran yeast sucrose agar (DYSG) or coconut agar fluorescence ≅ OTA production by Penicillium
verrucosum
Ochratoxin A (OTA)
NH
O
O
OH
Cl
O
CH3
OHO
relatively stable bioaccumulative detected in human milk and serum
potentially carcinogenic to humans, neurotoxicity, immunotoxicity
Human Exposure to OTA cereals and cereal-based foods major contributor to
OTA intake 60- 75% of estimated dietary exposure for Canadians
(Kuiper-Goodman et al. 2010)
International Limits for OTA
Worldwide regulations for mycotoxins in food and feed in 2003 (FAO, 2004)
CFIA: swine diets (kidney damage) 0.2 mg/kg swine diets (reduced weight gain) 2 mg/kg poultry diets 2 mg/kg
Health Canada's proposed Maximum Limits and Guidance Values for OTA
Proposed Value (µg/kg) (under consideration as a guideline) •Raw cereal grains (i.e., wheat, barley, oats, rice) 5 µg/kg
Proposed Maximum Limits (ML) (µg/kg) •Wheat bran 7 µg/kg •Directly consumed cereal grains (e.g. bulgur wheat, rice, oats, pearled barley) and cereal-derived products (e.g. flour; finished foods such as bread and breakfast cereals) 3 µg/kg •Grape juice 2 µg/kg
•Dried vine fruit (e.g. raisins) 10 µg/kg •Infant formulas and cereal-based foods for infants and young children 0.5 µg/kg http://www.hc-sc.gc.ca/fn-an/securit/chem-chim/toxin-natur/summary-resume-eng.php
Occurrence of OTA in Canadian Grains
cereals
< LOQ
1 – 5 µg/kg
> 5 µg/kg
oilseeds and pulses
< LOQ
1 – 5 µg/kg
> 5 µg/kg
OTA in wheat shipments vary throughout the year
Loading date
Jan Jul Jan Jul Jan Jul Jan Jul Jan Jul Jan
mea
n O
TA (n
g/g)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Production of OTA during Grain Storage
Not a disease of field crops Different from DON issue P. verrucosum growth and
OTA production is driven by moisture content / water
availability temperature
(Abramson et al. 1990)
<LOQ set to 0
Ergosterol (mg/kg)
0 1000 2000 3000 4000 5000 6000 7000
OTA
+ O
TB (m
g/kg
)
0
50
100
150
200
oats wheat Plot 1 Regr
b22.3778746483m0.0161245625r ²0.3344330222
b-3.4532320036m0.084628713r ²0.4533044545
Ochratoxin Production vs. Fungal Biomass Wheat vs. Oats
Mould growth not a good indicator for contamination of grain with OTA and other mycotoxins
Production of OTA by different strains of Penicillium verrucosum
Penicillium verrucosum strain
OTA
(ng/
g)
0
20
40
60
80
100
Intensity of Fluorescence on Agar Media
C27-1
CIT – OTA –
C1136-1
CIT +++ OTA ++
C84-2
CIT – OTA +++
C618-2
CIT + OTA –
Heterogeneity Issues for OTA
analysis of 100 single wheat kernels from incubation experiment for OTA
OTA (ng/g) n < 20 22 20 - 100 14 100 - 1000 42 1000 - 2000 18 2000 – 10,000 3 > 10,000 1
Relationship between OTA contamination and colonization by P. verrucosum
Relationship between OTA and Penicillium verrucosum concentrations in wheat
R2 = 0.6488
0
200
400
600
800
1000
1200
1400
1600
1800
0 1 2 3 4 5 6 7
OTA (ppb)
Pv (p
pm)
sampleLinear (sample)
Bulk Sampling — Heterogeneity of Distribution
70 – 75,000 tonnes
whole grain incremental samples
composite sample 10 kg
ground test portion 10 – 100 g
Storage in Grain Silos
Optimized aeration: Understanding the Equilibrium Moisture Content (EMC) Critical control
points include: Aerated floors,
elevator & augers, man hole, down spouts
Grain Storage in Bags Ground drainage crucial, drainage tiles under plastic Top surface smooth to aid in drainage Condensation under plastic needs to be controlled with
aeration Run piles north – south to allow sun to dry off sides Plastic sheeting needs replacement after one season
Management of (Temporary) Grain Storage is Extremely Important (NDSU) Check frequently for heating, sweating, moisture
accumulation and general condition of stored grain Fence in the pile to keep animals away and plastic
sheeting intact Cool temperatures and aeration minimize mould
growth, limit moisture migration, and control insects Temporary grain storage usually is for less than 6-7
months! After that grain should be sold or moved to permanent storage before warm spring weather arrives
Additional Sources of Information
http://www.grainscanada.gc.ca/storage-entrepose/ota/ota-eng.htm http://www.grainscanada.gc.ca/storage-
entrepose/ssg-de-eng.htm http://www.usask.ca/agriculture/plantsci/winter_cere
als/winter-wheat-production-manual/chapter-23.php http://www.ag.ndsu.edu/publications/crops/grain-
drying-storage/ http://lancaster.unl.edu/ag/crops/storage.shtml
Photograph acknowledgement
http://www.slu.se/sv/institutioner/mikrobiologi/forskning/eukaryot-mikrobiologi/xerofila-svampar/ http://www.omafra.gov.on.ca/english/engineer/facts/8
5-003.htm http://www.kryan.com/Baggers.html http://www.johnbob.ca/images/ http://www.versacorporation.com/