Transcript Fungal Overview - International Coffee Organization

Good Hygiene Practices along the coffee chain
Module 1.1
Fungal Overview
Background: yeasts and moulds (fungi) in food
 Eukaryotic cell structure
 More complex than prokaryotic (bacteria)
 Yeasts
 Unicellular (3 – 5μm)
 Can divide rapidly (but slower than bacteria 2-3h)
 Moulds
 Tubular cells (30 - 100μm) (hyphae)
 Grow by apical extension (can grow very long filamentous fungi)
 Reproduce by sexual and asexual production of
spores
 Adapted to lower moisture conditions than
most bacteria
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Module 1.1 – Fungal Overview
Background: fungi in food
 ‘Useful’ fungi
 Edible mushrooms
 Used in processing / preservation
 Spoilage fungi
 Can grow on foods with lower available water than
most bacteria (some as low as aw = 0.65)
 Typically spoil semi-moist foods – cheeses, cured
meats, bread, cakes, fruit preserves etc
 Cereals, grains, nuts, coffee, cocoa that are
incorrectly stored (damp, moist conditions) – huge
food and feed losses annually
 Toxigenic fungi
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Module 1.1 – Fungal Overview
Toxigenic fungi: Overview of mycotoxins
 Fungal metabolites
 When ingested, inhaled or absorbed through skin cause lowered
performance, sickness or death in man or animals, including birds.
 Acute effects
• Headache, fever, nausea, diarrhœa, vomiting, weakness, tremors,
convulsions
• In some cases death
 Chronic or long-term effects
• Cancer
• Genetic or birth defects
 Over 200 kinds of mycotoxin, produced by about 150 different
fungi
 Certain crops are commonly associated with certain mycotoxins
 Ecological associations of mould with crop plants
 Certain post-harvest conditions can favour certain moulds
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Module 1.1 – Fungal Overview
Mycotoxins of major significance
Mould species
Slide 5
Mycotoxins
Aspergillus parasiticus
Aflatoxins B1, B2, G1, G2
Aspergillus flavus
Aflatoxins B1, B2
Fusarium sporotrichiodes
T-2 toxin
Fusarium graminearum
Deoxynivalenol, Zearalenone
Fusarium moniliforme
Fumonisin B1
Penicillium verrucosum
Ochratoxin A
Aspergillus ochraceus
Ochratoxin A
Penicillium expansum
Patulin
Module 1.1 – Fungal Overview
Aflatoxins
 Commonly associated with maize,
groundnuts, tree nuts, spices,
dried fruit etc.
 Carry-over from animal feed to
foods of animal origin for humans:
e.g. Aflatoxin M1 in milk
 International guidelines exist for
prevention and control
Slide 6
Module 1.1 – Fungal Overview
CYA
CBS
CZ
Other important mycotoxins
 Trichothecenes – Fusarium spp
 Associated with a variety of cereals and wet harvest
conditions
 Zearalenone – Fusarium spp
 Associated with maize grown in temperate climates
 Fumonisins – Fusarium spp
 Primarily associated with maize
 Patulin - Penicillium spp, Aspergillus spp
 Associated with apple products
 Ochratoxin – Aspergillus spp, Penicillium spp
 Associated with cereals, wine, grape juice, dried fruit,
coffee and cocoa
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Module 1.1 – Fungal Overview
OTA contamination in coffee
 OTA long known as a renal toxin and carcinogen which is also
teratogenic (produces birth defects)
 Evidence of genotoxicity published in the early 1990’s - if true,
categorizes OTA with aflatoxin
 Studies in Europe on dietary exposure concluded the most
significant sources are grain and grain products; beer; wine; dried
fruit; coffee
 Several countries have already adopted maximum levels of
contamination in coffee
 Some importers have rejected contaminated batches
 EU harmonised limits for roasted and soluble coffees - in force
from January 2005
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Module 1.1 – Fungal Overview
OTA producers in coffee

OTA producers in coffee:
 Aspergillus ochraceus (and related)
 Aspergillus carbonarius
A. Colonies of A. flavus from
Aspergillus flavus group. B. & C.
 Aspergillus niger complex

Elsewhere:
Typical colonies of Penicillium spp.
 Penicillium verrucosum
 Penicillium nordicum

These organisms interact with other coffee-associated organisms,
and not just Coffee Berry Borer (CBB) and Colletotrichum etc. The
fungi include:
 Fusarium stilboides
 Candida edax
 Cryptococcus album

•Cladosporium spp.
•Penicillium brevicompactum
•Auriobasidium pululans
•Eurotium repens
Additional context are the conditions man’s activities impose in the
orchard and during processing and trading
Slide 9
Module 1.1 – Fungal Overview
C
A
B
Conditions for activity of OTA producers

Not all isolates of a species that is known to produce a mycotoxin will do
so:
 A. niger complex  5% usually weak
 A. carbonarius  80% often strong
 A. ochraceus and similar  80% often strong

The range of conditions over which a mycotoxin producer can grow is
broader than those over which it can produce mycotoxin:
 A. niger complex: Aw and temperature limits n.a.
 A. carbonarius: Aw limits  0.92 and 0.85 temperature limits  35˚C and 37˚C
 A. ochraceus: Aw limits  0.82 and 0.78 temperature limits  40˚C and 42˚C
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The interaction of physiological and ecological properties is too complex thus laboratory studies are only indicative
At this stage of our understanding, only field studies can clarify the
limiting conditions for OTA contamination in coffee production
Slide 10
Module 1.1 – Fungal Overview
Effect of pH and Aw on mould growth
Xerophile
pH 3.0
Aw
0.99+
0.98
X
H
4.0
5.0
Mesophile
7.0
pH 3.0
Aw
0.99+
4.0
5.0
Hydrophile
7.0
pH 3.0
Aw
0.99+
0.98
0.98
0.94
0.94
0.94
0.905
0.905
0.905
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Module 1.1 – Fungal Overview
4.0
5.0
7.0
Factors controlling mould growth
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Initial contamination?
Oxygen / gaseous environment?
Nutrients?
Temperature?
Water activity?
Aw =
 What is it?
 How do we measure it?
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Module 1.1 – Fungal Overview
Moisture content (m.c.) and Aw
Slide 13
0.9
0.8
0.5
0.6
0.7
+
0.4

++
0.3

m.c. describes the
sample; Aw predicts
microbial growth
potential
In commerce, m.c. is
measured but the
microbial stability is only
predicted by Aw so we
need to inter-convert
So we need to understand
the precision of this interconversion
aw

1.0
Cherry robusta
10
20
Module 1.1 – Fungal Overview
30
40
mc
50
60
Evaluating moisture in commodities
Moisture content - dry or wet basis?
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Chemical methods
Oven method
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Temperature?
Time?
Air circulation?
Vacuum?
Electrical methods
 Capacitance
 Conductance
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Other gravimetric methods
Empirical / traditional sensory methods
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Module 1.1 – Fungal Overview
Evaluating moisture in commodities
Water activity
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Internal equilibration?
Equilibration with chamber air?
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Module 1.1 – Fungal Overview
Precision and accuracy of measurement
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Uniformity of
commodity
Sampling
Calibration
One type of low-cost
moisture meter
investigated under the
‘global coffee project’
 Methodology
 Frequency
 Quality of standards

SINAR moisture meter
Instrument stability
 Robustness
 Kind of use
Slide 16
‘EDABO’ distillation method of moisture
determination developed in Brazil
Module 1.1 – Fungal Overview
Moisture and Aw in complex systems

The husk is more
hygroscopic than the
bean - it forms a
barrier that slows
water loss during
drying and slows
water ingress during
re-wetting.
From the perspective
of mould growth, the
significance of a
given moisture
content of bean and
cherry is quite
different.
Slide 17
100
y = -0.0585x2 + 3.7691x + 30.236
R2 = 0.9774
90
OTA
prod
80
e.r.h.

bean
husk
70
hsk
limit
60
bn
y = -0.0459x2 + 3.2896x + 26.158
R2 = 0.979
50
40
0
10
20
30
40
m .c. (db)
BEAN LIMIT-
Module 1.1 – Fungal Overview
-HUSK LIMIT
50