Fungal Overview by w84peG2

VIEWS: 24 PAGES: 17

									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



Slide 2                   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 3                   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 4                        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 5                        Module 1.1 – Fungal Overview
                     Aflatoxins

 Commonly associated with maize,
  groundnuts, tree nuts, spices,                       CYA


  dried fruit etc.
                                                 CBS


 Carry-over from animal feed to                        CZ

  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
                  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 7                       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 8                  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 niger complex           Aspergillus flavus group. B. & C.         C
                                                       Typical colonies of Penicillium spp.       A   B
        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       •Cladosporium spp.
                                          •Penicillium brevicompactum
               Candida edax              •Auriobasidium pululans
               Cryptococcus album        •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
          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 10                            Module 1.1 – Fungal Overview
                    Effect of pH and Aw on mould growth


              Xerophile                          Mesophile                           Hydrophile
 pH 3.0            4.0   5.0   7.0    pH 3.0        4.0    5.0     7.0      pH 3.0     4.0   5.0   7.0
Aw                                   Aw                                    Aw
0.99+                                0.99+                                 0.99+



0.98      X
          H                          0.98                                  0.98


0.94                                 0.94                                  0.94



0.905                                0.905                                 0.905




        Slide 11                            Module 1.1 – Fungal Overview
                  Factors controlling mould growth

        Initial contamination?
        Oxygen / gaseous environment?
        Nutrients?
        Temperature?
        Water activity?        Aw =
                What is it?
                How do we measure it?




    Slide 12                     Module 1.1 – Fungal Overview
                Moisture content (m.c.) and Aw
                                                                  Cherry robusta

        m.c. describes the




                                             1.0
         sample; Aw predicts




                                             0.9
         microbial growth
         potential




                                             0.8
                                                        ++    +



        In commerce, m.c. is




                                             0.7
         measured but the


                                        aw
                                             0.6
         microbial stability is only
         predicted by Aw so we

                                             0.5
         need to inter-convert
                                             0.4
        So we need to understand
                                             0.3


         the precision of this inter-
         conversion                                10        20   30        40     50   60
                                                                       mc



    Slide 13                  Module 1.1 – Fungal Overview
               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



Slide 14                          Module 1.1 – Fungal Overview
           Evaluating moisture in commodities

                       Water activity

      Internal equilibration?
      Equilibration with chamber air?




Slide 15             Module 1.1 – Fungal Overview
       Precision and accuracy of measurement

    Uniformity of
     commodity
    Sampling
                                   One type of low-cost
    Calibration                      moisture meter
                                  investigated under the
            Methodology          ‘global coffee project’           SINAR moisture meter

            Frequency
            Quality of standards
    Instrument stability
            Robustness
                                          ‘EDABO’ distillation method of moisture
            Kind of use                     determination developed in Brazil


Slide 16                   Module 1.1 – Fungal Overview
               Moisture and Aw in complex systems

        The husk is more
         hygroscopic than the                    100          y = -0.0585x2 + 3.7691x + 30.236
         bean - it forms a                                               R2 = 0.9774
                                                 90
         barrier that slows      OTA
         water loss during       prod
                                                 80                                                           bean
                                                                                                              husk
         drying and slows



                                        e.r.h.
                                                 70
                                                                                                              hsk
         water ingress during    limit
                                                 60                                                           bn
         re-wetting.                                                       y = -0.0459x2 + 3.2896x + 26.158
                                                 50                                   R2 = 0.979
        From the perspective
         of mould growth, the                    40
                                                       0       10        20       30       40       50
         significance of a
                                                                          m .c. (db)
         given moisture
         content of bean and
                                                           BEAN LIMIT-        -HUSK LIMIT
         cherry is quite
         different.

    Slide 17                    Module 1.1 – Fungal Overview

								
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