View
213
Download
0
Category
Preview:
Citation preview
Good Hygiene Practices along the coffee chain
Fungal Overview
Module 1.1
Slide 2 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
Slide 3 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
Slide 4 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
Slide 5 Module 1.1 – Fungal Overview
Mycotoxins of major significance
Mould species 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
Slide 6 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
CZ
CBS
CYA
Slide 7 Module 1.1 – Fungal Overview
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
Slide 8 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
Slide 9 Module 1.1 – Fungal Overview
OTA producers in coffee
OTA producers in coffee: Aspergillus ochraceus (and related) Aspergillus carbonarius Aspergillus niger complex
Elsewhere: 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
Additional context are the conditions man’s activities impose in the orchard and during processing and trading
•Cladosporium spp. •Penicillium brevicompactum•Auriobasidium pululans•Eurotium repens
A. Colonies of A. flavus from Aspergillus flavus group. B. & C. Typical colonies of Penicillium spp.
AC
B
Slide 10 Module 1.1 – Fungal Overview
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 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 11 Module 1.1 – Fungal Overview
Effect of pH and Aw on mould growth
XH
Xerophile
pH 3.0 4.0 5.0 7.0Aw0.99+
0.98
0.94
0.905
Hydrophile
pH 3.0 4.0 5.0 7.0Aw0.99+
0.98
0.94
0.905
Mesophile
pH 3.0 4.0 5.0 7.0Aw0.99+
0.98
0.94
0.905
Slide 12 Module 1.1 – Fungal Overview
Factors controlling mould growth
Initial contamination? Oxygen / gaseous environment? Nutrients? Temperature? Water activity?
What is it? How do we measure it?
Aw =
Slide 13 Module 1.1 – Fungal Overview
Moisture content (m.c.) and Aw
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 inter-conversion
10 20 30 40 50 60
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
mc
aw
Cherry robusta
+++
Slide 14 Module 1.1 – Fungal Overview
Evaluating moisture in commodities
Chemical methods Oven method
Temperature? Time? Air circulation? Vacuum?
Electrical methods Capacitance Conductance
Other gravimetric methods Empirical / traditional sensory methods
Moisture content - dry or wet basis?
Slide 15 Module 1.1 – Fungal Overview
Evaluating moisture in commodities
Internal equilibration? Equilibration with chamber air?
Water activity
Slide 16 Module 1.1 – Fungal Overview
Precision and accuracy of measurement
Uniformity of commodity
Sampling Calibration
Methodology Frequency Quality of standards
Instrument stability Robustness Kind of use
‘EDABO’ distillation method of moisture determination developed in
Brazil
SINAR moisture meter
One type of low-cost moisture meter
investigated under the ‘global coffee
project’
Slide 17 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.
y = -0.0585x2 + 3.7691x + 30.236R2 = 0.9774
y = -0.0459x2 + 3.2896x + 26.158R2 = 0.979
40
50
60
70
80
90
100
0 10 20 30 40 50
m.c. (db)
e.r
.h.
bean
husk
hsk
bn
BEAN LIMIT- -HUSK LIMIT
OTA prod limit
Recommended