FEED PRESERVATION AND MYCOTOXIN MANAGEMENT: ARE WE TALKING ABOUT THE SAME THING?
Dr. Rui Alexandre Gonรงalves Aquaculture and Mycotoxin Expert Aquaculture Business Developer - Lucta S.A. Innovation Division - Feed Additives UAB Research Park, Bellaterra, Barcelona, Spain
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Importance of fungi for the ecosystem is immeasurable! Fungi are present in all terrestrial habitats, from Antarctica to the hot deserts of Namibia, and in most aquatic environments. Fungi are opportunistic heterotrophs, they can penetrate solid substrates (e.g., rock, bark, dead branches, bare soil or grains), and nutritionally exploit almost any food substrate in the world.
Therefore, will not be a surprise if you find fungi in grains or even in fishmeal!
Not all fungi are bad! Several species of fungi, namely from genus Penicillium, play an important role in various industries.
For example, penicillin, produced by P.
chrysogenum (formerly P. notatum), discovered by Alexander Fleming in 1929, was probably the most important discovery in last century as it changed the course of medicine.
Fungi also play a central role in the food industry (cheese and various meat products) and are becoming increasingly important in the biotechnology field, especially
Food industry
Biotechnology field (enzymes)
Cheese Meat products
Gluconic, citric, and tartaric acids Pectinases Lipase Amylases and cellulases Proteases
on the production of enzymes (e.g. gluconic, citric, and tartaric acids, several pectinases, lipase, amylases, cellulases, and proteases).
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Some of the fungi can have a parasitic
Fungi attack almost all known taxa
behaviour and in certain cases can
of plants and animals, including
be pathogenic as their ability to
shrimp (e.g. Fusarium spp. in penaeids)
penetrate almost any surface can
and fish (e.g. Saprolegniasis).
be used to invade host organisms.
Focusing on fungi as plant pathogens, they attack all parts and all stages of crop plant development (from root hair to apical buds, grains or fruits). The fungal infections may be restricted to small leaf spots, or they may be systemic, killing their host very quickly or remaining invisible until it is time to benefit from crucial energy resources, such as those concentrated by the host in anthers, bulbs or seeds.
Not all secondary metabolites are mycotoxins Fungal metabolism produces an
Toxic to bacteria: antibiotics
apparently endless diversity of organic compounds, which are
Toxic to plants: phytotoxins
not obviously required for normal growth and metabolism. These are
Toxic to animals: mycotoxins
called secondary metabolites. Not all secondary metabolites are mycotoxins. Simplistically, we could
The exact process of mycotoxin production by fungi is not
split them into three broad groups:
well understood. However, it is hypothesized that producing mycotoxins may be a strategy to out-compete another microorganism for plant nutrients (Rankin and Grau, 2002).
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Understanding fungal growth and mycotoxin production To develop effective strategies to
Besides the previously mentioned
control the impact of fungi and/or
factors contributing to the presence
mycotoxins in animal production it is
or production of mycotoxins, i.e.,
essential to understand fungal growth
environmental (temperature,
and mycotoxin production behaviour.
humidity), ecological conditions (e.g., insect attacks, physical plant
Fungal growth and, in
damage and general stress) are also
consequence, the occurrence
key and often beyond human control.
of individual mycotoxins is a result of complex interaction
For example, Ramírez et al.
of several factors, being
(2004) observed that the type
environmental conditions
of water stress, whether it is
-geography and climatic factors- the
caused by osmotic or matric
most relevant (Kuiper-Goodman,
forces, can impact the activity
2004; Miraglia et al., 2009; Paterson and Lima, 2010; Paterson and Lima, 2011; Ramirez et al., 2006).
and colonisation of cereal-based substrates by strains of F.
graminearum (the main producer of deoxynivalenol).
Behind these two main factors (geography and climatic factors)
Several studies on F. graminearum
biological requirements such as
from root and stalk rot of
temperature and water activity
cereals have shown optimum
(aw) play a critical role in fungal
water content and temperature
growth and consequent mycotoxin
for growth were 0.99–0.98
production (CAST, 2003; FAO, 2004;
aw at 20–30°C, changing to
Marth, 1992; Ramirez et al., 2006; Sweeney and Dobson, 1998).
0.95–0.96 aw at 35°C. However, conditions for optimum
However, fungal growth and
fungal growth and maximum
mycotoxin production are not
toxin production are not the
simple combinations of optimal
same (Ramírez et al., 2006).
temperature and water activity.
OPTIMUM WATER CONTENT & TEMPERATURE FOR GROWTH FOR F. GRAMINEARUM
20–30°C 0.99–0.98 aw 35°C 0.95–0.96 aw
FACTORS INFLUENCING FUNGAL GROWTH & MYCOTOXIN PRODUCTION Environmental conditions (geographic and climatic factors): Temperature & water activity Ecological conditions: insect attacks, physical plant damage and stress
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For example, Table 1 shows: Two species of storage fungi: Aspergillus flavus and
Penicillium verrucosum Two representatives of field fungi: Fusarium verticillioides and F. graminearum From the table is possible to clearly understand why Aspergillus spp. and Penicillium spp. are in competitive advantage to growth in storage conditions, as they can grow at extreme temperatures and with a lower water activity than Fusarium spp. In the case of Aspergillus flavus , they occur in warmer climates, whereas Penicillium verrucosum is adapted to growing in temperate regions, being able to grow at near 0°C.
Table 1. Preferred temperatures and water activity values for fungal growth. Fungus species
Aspergillus flavus
Temperature range for fungal growth (°C)
Water activity (aw) for fungal growth
Minimum
Optimum
Maximum
Minimum
Optimum
Maximum
10-12
25-35
42-43
0.80
0.95-0.99
-
Penicillium verrucosum
0
20
31-35
0.80
0.95
-
Fusarium verticillioides
2-5
22.5-30
32-37
0.87-0.9
-
0.99
-
24-26
-
0.9
-
0.99
F. graminearum
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Mycotoxin producing fungi
MYCOTOXINS PRODUCTION
Aflatoxins (AF), ochratoxin A (OTA), deoxynivalenol (DON), zearalenone (ZEN), fumonisins (FUM) and ergot alkaloids are the
FUSARIUM & CLAVICEPS
ASPERGILLUS & PENICILLIUM
PRE-HARVEST
POST-HARVEST
most common mycotoxins found in agriculture commodities and these are responsible for millions of dollars in annual losses worldwide.
In contrast, the important
Fusarium and Claviceps species infect crops before harvest.
These toxins are produced by just a few species from the common genera Aspergillus, Penicillium,
Fusarium, and Claviceps.
All Aspergillus and Penicillium FUSARIUM & CLAVICEPS
species are either commensals, growing in crops without obvious
ASPERGILLUS & PENICILLIUM
signs of pathogenicity, or they invade crops after harvest, producing toxins during drying and storage. The most important Aspergillus species, occurring in warmer
F. verticillioides is ubiquitous in maize, with an endophytic nature, producing fumonisins, which are generally more prevalent when crops are under drought stress or suffer excessive insect damage. It has recently been shown that Aspergillus niger also produces fumonisins, and several commodities may be affected.
climates, are A. flavus and A. parasiticus, which
F. graminearum, the major producer of deoxynivalenol and zearalenone, is pathogenic for maize, wheat, and barley, and produces these toxins whenever it infects these grains before harvest.
produce aflatoxins in maize, groundnuts, tree nuts, etc.
Penicillium verrucosum also produces ochratoxin A but occurs only in cool temperate climates, where it infects small grains.
Table 2. Preferred temperatures and water activity values for mycotoxin production. Fungus species
Aspergillus flavus
Water activity (aw) for mycotoxin formation
Temperature range for mycotoxin formation (°C)
Minimum
Optimum
Maximum
Minimum
Optimum
Maximum
0.82
0.99-0.99
0.99
12-15
30-33
37-40
Penicillium verrucosum
0.83-0.86
0.90-0.95
-
4
20-25
-
Fusarium verticillioides
0.92-0.93
-
-
10
15-30
37
F. graminearum
0.9-0.91
0.98
-
11
29-30
-
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Feed preservation and mycotoxin management: Complementary but not the same! Presence of moulds in crops, in raw materials or finished feeds may be the first indication that something is wrong with its hygiene/conservation. However, it will be hard to correlate the fungal presence with the potential presence of the mycotoxin and vice-versa (Alinezhad et al., 2011; Greco et al., 2015).
Extending the knowledge of fungal growth in crops There are several reasons why
For example, Fusarium oxysporum
For example, Fusarium spp. are
raw material or finished feeds
and Fusarium solani, are known
field fungi usually lacking the
may get mouldy, from improper
as opportunistic pathogens for
ability to grow on dry feed.
storage conditions (high humidity,
fish and shrimp (Hatai et al., 1986;
However, the toxins produced
high variations in temperatures
Lightner, 1996; Ostland V.E. et al., 1987; Souheil et al., 1999).
by these fungi species (e.g.,
leading to condensation, etc.) to a poor manufacturing process (e.g.,
DON) will remain stable on the plant raw materials used
insufficient drying time, lack of
Moreover, fungal presence in feed may
to manufacture aquafeeds,
preservatives/anti-moulds, etc.).
also reduce its palatability and therefore
and in some cases, even be
intake of the feed, leading to economic
redistributed and concentrated
In finished feeds, fungal
losses, possible health consequences
in certain milling fractions
contamination can also originate
and unavoidable environmental impact.
(Cheli et al., 2013) e.g., corn vs corn gluten meal (Gonรงalves et al., 2018b).
from an inappropriate selection of ingredients, which can carry
Mycotoxins produced on crops, i.e., in
fungal spores that are resistant
the field (which is the case for example
to extrusion/pelleting, having the
of DON and FUM) will remain in raw
capacity to germinate afterwards
materials, even after processing, due
(due to improper storage or poor
to their heat stability (Pitt, 2014).
manufacturing processes). However, it is important to highlight that the presence of fungi might not represent a mycotoxin threat, but it can be a direct risk for the host.
While fungi will probably be destroyed due to high temperatures, mycotoxins will certainly remain in those materials.
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Mycotoxin redistribution and
Mycotoxin occurrence is sometimes
transfer from crops to aquafeeds
described to be limited to certain
is well identified and has been
regions, depending on the type of
observed and reported (Cheli et al.,
mycotoxin and highly associated,
2013; Gonรงalves et al., 2018b).
as mentioned before, to the conditions for fungal growth and
The fate of mycotoxins
mycotoxin production.
during cereal processing, such as sorting, cleaning,
Is true that environmental
milling and thermal processes
conditions will geographically
has been studied by several
restrict mycotoxin production,
authors. However, their level
however, the globalized feed grain
in feedstuffs is variable and
trade may distribute mycotoxins
affected by several factors:
outside of their natural occurrence geographical areas, complicating
Type of mycotoxins
the estimation of mycotoxin
(polar or apolar)
contamination in compound feed.
Level and extent of fungal contamination Complexity of the cereal
Therefore, the only secure method of
processing technology
preventing unpleasant surprises is to test the raw materials for mycotoxin presence.
Therefore, the use of feed preservatives may reduce the production of mycotoxins from the moment they are added on, however, they will not have any impact on mycotoxins already present in ingredients or feeds produced prior to its addition.
Consequently, mycotoxin management solutions will be complementary to feed preservation.
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Some take-home messages Not all molds produce mycotoxins and even the ones that have that capacity, may be present without producing any toxin. Thus, the confirmation of mold contamination does not mean the presence of mycotoxins. As a result, the use of mold inhibitors does not guarantee that feed is free of mycotoxins, as they are also produced in crops and not destroyed during processing. It is recommended that aquafeed and aquaculture producers regularly monitor raw materials and finished feeds for mycotoxin contamination, either through on-site rapid testing or through an external laboratory that may be equipped with more reliable detection system.
In cases where feed quality has been compromised by the presence of mycotoxins, the use of a mycotoxin deactivator is advised.
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