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Food Analysis > Lecture 16 - Mycotoxins > Flashcards

Lecture 16 - Mycotoxins Flashcards

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1
Q

what are mycotoxins?

A

the toxins produced when molds (filamentous fungi) develops on food commodities)

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2
Q

what are hte main producers of mycotoxins?

A

fungal species belonging to the genera Asperigillus, Fusarium and Penicillin

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3
Q

what are the major classes of mycotoxins?

A
  1. aflatoxins
  2. ochratoxins
  3. trichothecens
  4. fumoisins and patulin
  5. zearalenone
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4
Q

what are examples of aflatoxins?

A

B1; B2; M1; M2; G1 and G2

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5
Q

what are examples of ochratoxins?

A

ochratoxin A

OTA

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6
Q

what are examples of trichothecens

A

DON (deoxynivalenol)
T2
HT2

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7
Q

what are examples of fumonisins

A

FBs: FB1, FB2, FB3

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8
Q

where are patulins found?

A

apples and apple products

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9
Q

what is the order of the food chain “farm to plate”

A
  1. preharvest farm
  2. harvest farm
  3. post harvest storage
  4. processing factory
  5. distribution transportation
  6. marketing wholesalers and retailers
  7. consumption
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10
Q

what are 2 categories of mold?

A
  1. field fungi

2. storage fungi

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11
Q

where are aflatoxins found?

A 
sorghum
soybeans
corn
wheat
barley
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12
Q

where are trichothecens found?

A 
barley
oats
sorghum
soybeans
corn
wheat
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13
Q

where are zearalenone found?

A 
wheat
sorghum
corn
barley
silage (forage grass, legume crops and corn)
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14
Q

what are the 3 methods of control and detoxification?

A
  1. physical methods: grinding and rinsing, heat treatment, irradiation, degradation, inorganic absorption
  2. chemical methods: alkalization, ozone degradation
  3. biological methods: microbial absorption, microbial degradation, biological degradation
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15
Q

examples of AFB1?

describe the properties of AFB1

A
  • eg. aspergillus flavus and aspergillus parasiticus

solubility:
- soluble in polar organic solvents
- poorly soluble in water
- insoluble in petroleum ether, ethyl acetate and hexane

pH:

  • stable in neutral solutions
  • resistant to strong acids
  • rapid decomposition in alkaline

UV:

  • produces fluoresence (group B&G)
  • destructive for low conc of AFB1

heat:

  • stable in 200deg C
  • decomposed until 268degC
  • hard to destroy under normal temp
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16
Q

what are examples of Zearalenone ZEN

describe properties

A

eg. fusarium graminearum and fusarium culmorum

solubility:

  • insoluble in water
  • slightly soluble in hexane
  • more soluble in benzene, acetonitrile, methylene, chloride, methanol, ethanol, acetone
  • soluble in aqueous alkali

pH:

  • stable in neutral and acidic
  • ester bond will be open in alkaline environment

UV:
- exhibits blue-green

heat:

  • melting point is 161degC
  • hard to destroy under normal cooking
17
Q

what are examples of deoxynivalenol?

describe properties

A

eg. fusarium and gibberella

solubility:

  • soluble in water and polar solvents
  • insoluble in hexane and diethyl ether

pH

  • sensitive in alkaline environment
  • stable in neutral and acid

UV:

  • absorption peak under short wave UV
  • decomposes under high tense UV

heat

  • resistant to heat
  • stable in 120degC for 1 hr
  • decomposes at 150degC for 15 min
18
Q

what are the types of pre-treatment/extraction in mycotoxin analysis

A
  1. liquid-liquid extraction (LLE)
  2. supercritical fluid extraction (SFE)
  3. solid phase extraction (SPE)
  4. solid phase micro-extraction (SIME)
19
Q

what are 3 types of clean up detection in mycotoxin analysis?

A
  1. thin layer chromatography
  2. gas chromatography
  3. high performance liquid chromatography
20
Q

how is a mycotoxin sampling plan defined?

A

by a mycotoxin test procedure and a defined accept/reject limit

21
Q

how much can the number of containers sampled vary?

A

can vary from 1/4th (for small containers less than 20 metric tons) to the square root of the total number of containers (for large containers greater than 20 metric tons)

22
Q

in sampling, how do you ensure that the analytical test portion has the same conc of toxins as the original sample?

A

the whole primary sample must be ground and mixed

23
Q

describe the liquid-liquid extraction

A
  • two immiscible phases shaken together

- compounds partition to their preferred phase (into aqueous or organic solvent)

24
Q

describe the solid phase extraction/clean up and concentration

what are advantages?

A
  • SPE is based on molecularly imprinted polymers that are syntehtic receptors for the mycotoxins
  • used for sample extraction, clean up and concentration
  • C18 (octadecylsilane), silica gel, anionic and cationic exchange materials, immunosorbets and molecular imprinted polymers

adv
- faster and most popular method

25
Q

describe the solid phase concentration

what are advantages?

A
  • uses immunoaffinity columns (IACs)
  • used for purification of samples which are contaminated with different mycotoxins
  • the mycotoxins (analytes) are bound selectively to the antibodies on the column
  • rinsing removes most possible interferences. toxins can be eluted by antibody denaturation

adv:
- offers high selectivity

26
Q

describe thin layer chromatography (TLC)

what gel is used?

what are advantages and disadv?

A
  • used for detection step (for quantitative and semi-quantitative measurements of mycotoxins)
  • detects by fluorodensitometry or visual procedures
  • uses silica gel, F254 fluorescent silica gel, or silica gel impregnated with organic acid (for detection of aflatoxins, citrinin, fumonisin)

adv:

  • costs less
  • simple
  • rapid screening

dis
- lack of automation has let to TLC being replaced by other techniques

27
Q

describe gas chromatography for detection

A
  • detection is achieved by linking the system to mass-spectrometry (MS), flame ionization or fourier transform infrared spectroscopy
28
Q

why is GC not a technique suitable for commercial purposes?

A

not suitable for commercial purposes because of its limitations to volatile and thermostable compounds

29
Q

when detecting mycotoxins with GC, why do mycotoxins need to be derivatised first?

what are examples of chemical reactions used for derivatisation?

A

since mycotoxins are not volatile

thus, derivitisation by chemical reactions (eg. silylation or polyfluoroacylation) are needed in order to be quantified

30
Q

what is the most widely accepted official method for determination of mycotoxins?

A

HPLC

high performance liquid chormatography

31
Q

describe detection by HPLC

A

HPLC = high performance liquid chromatography

32
Q

what kind of detection is used in HPLC?

A

UV
fluorescence
amperometric
spectrofluorimetric

33
Q

how can mycotoxins be detected directly by HPLC-fluorensence (HPLC-FD)

A

when mycotoxins have natural fluorescence (ochratoxin or citrinin)

34
Q

what has increased detection sensitivity in comparison to HPLC-FD?

A

Mass spectroscopy with electrospray or pressure chemical ionization

35
Q

what is thel imit of detection by HPLC-MS?

A

0.1 and 1 microg/Kg

36
Q

what are advantages of HPLC?

disadv?

A

adv

  • high resolution
  • improved limit of detection
  • possibility to be coupled to multiple detection automated systems

disadv:
- most chromatographic assays are expensive, time consuming and require expensive equipment and clean up

37
Q

what is ELISA?

A

enzyme linked immuno sorbent assay

  • based on the ability of a specific antibody to distinguish the 3D structure of a specific mycotoxin
  • the direct competitive ELISA is commonly used in mycotoxin analysis

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