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Fungal Overview

Module 1.1. Fungal Overview. Eukaryotic cell structure More complex than prokaryotic (bacteria) Yeasts Unicellular (3 – 5 μ m) Can divide rapidly (but slower than bacteria - 2-3h) Moulds Tubular cells (30 - 100 μ m) ( hyphae )

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Fungal Overview

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  1. Module 1.1 Fungal Overview

  2. 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 Background: yeasts and moulds (fungi) in food Module 1.1 – Fungal Overview

  3. ‘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 Background: fungi in food Module 1.1 – Fungal Overview

  4. 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 Toxigenic fungi: Overview of mycotoxins Module 1.1 – Fungal Overview

  5. Mycotoxins of major significance Module 1.1 – Fungal Overview

  6. CYA CBS CZ 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 Module 1.1 – Fungal Overview

  7. Other important mycotoxins • Trichothecenes – Fusariumspp • Associated with a variety of cereals and wet harvest conditions • Zearalenone – Fusariumspp • Associated with maize grown in temperate climates • Fumonisins – Fusarium spp • Primarily associated with maize • Patulin - Penicilliumspp, Aspergillusspp • Associated with apple products • Ochratoxin – Aspergillus spp, Penicillium spp • Associated withcereals, wine, grape juice, dried fruit, coffee and cocoa Module 1.1 – Fungal Overview

  8. 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 Module 1.1 – Fungal Overview

  9. A. Colonies of A. flavus from Aspergillus flavus group. B. & C. Typical colonies of Penicillium spp. C A B 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 Module 1.1 – Fungal Overview

  10. 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 Module 1.1 – Fungal Overview

  11. Mesophile pH 3.0 4.0 5.0 7.0 Aw 0.99+ 0.98 0.94 0.905 Hydrophile pH 3.0 4.0 5.0 7.0 Aw 0.99+ 0.98 0.94 0.905 pH 3.0 4.0 5.0 7.0 Aw 0.99+ 0.98 0.94 0.905 Effect of pH and Aw on mould growth Xerophile X H Module 1.1 – Fungal Overview

  12. Aw = Factors controlling mould growth • Initial contamination? • Oxygen / gaseous environment? • Nutrients? • Temperature? • Water activity? • What is it? • How do we measure it? Module 1.1 – Fungal Overview

  13. 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 Module 1.1 – Fungal Overview

  14. Evaluating moisture in commodities Moisture content - dry or wet basis? • Chemical methods • Oven method • Temperature? • Time? • Air circulation? • Vacuum? • Electrical methods • Capacitance • Conductance • Other gravimetric methods • Empirical / traditional sensory methods Module 1.1 – Fungal Overview

  15. Evaluating moisture in commodities Water activity • Internal equilibration? • Equilibration with chamber air? Module 1.1 – Fungal Overview

  16. One type of low-cost moisture meter investigated under the ‘global coffee project’ SINAR moisture meter ‘EDABO’ distillation method of moisture determination developed in Brazil Precision and accuracy of measurement • Uniformity of commodity • Sampling • Calibration • Methodology • Frequency • Quality of standards • Instrument stability • Robustness • Kind of use Module 1.1 – Fungal Overview

  17. OTA prod limit BEAN LIMIT- -HUSK LIMIT 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. Module 1.1 – Fungal Overview

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