Feed preservation and mycotoxin management: Are we talking about the same thing?

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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