Phytogenic feed additives to counteract mycotoxin impact on fish health

Fernando J. Sutili, ELOAQUA Consulting

Phytogenic feed additives

Phytogenic feed additives (PFAs), also known as phytobiotics or botanicals, are plant-derived natural bioactive compounds which may be incorporated into animal feeds for purposes of improving health and welfare. Being derived from herbs, spices and other plants, PFAs are commercialized as extracts, essential oils, dried powder and isolated compounds as well as mixtures of these forms.

In fish production, PFAs may be used as food flavorings, antimicrobials, immunomodulators, antioxidants, digestive stimulants and technological additives to enhance feed quality and safety. One major advantage of PFAs lies in the fact that they are generally safe and do not trigger the side effects often associated with synthetic chemical utilization. In addition, they are cost-effective and environmentally friendly. Such properties and advantages make PFAs excellent growth promoters to be used in farmed fish.

Antifungal properties

Even though bacteria and viruses are considered more important animal pathogens than fungi, these have a major relevance regarding pathogens on plants. In agricultural production, plant-pathogenic fungi are the major cause of yield losses. Throughout evolution, plants have developed a wide variety of defense mechanisms to protect against fungal attack. In nature, plants synthesize a vast array of phytochemicals which play a role in protection strategies. By exerting

Table 1. Observed benefits of including phytogenic feed additive (PFAs) in aflatoxin B1 (AFB1)-contaminated fish diets.

PFAs Fish species Benefits

Rosemary

Fennel essential oil

Oreochromis niloticus

O. niloticus

Black pepper

O. niloticus

Rosemary and thyme powder Cyprinus carpio

Reduced the deleterious effects of AFB1 on growth, innate immunity and antioxidant activity.

Mitigated the impact of AFB1 on immunological and antioxidant responses; decreased AFB1 residues in musculature and liver.

Reduced growth impairment caused by AFB1; lowered AFB1 residues in whole fish body.

Restored digestive enzymes activity to near normal level.

Decreased AFB1-induced growth and innate immunity suppression.

Thyme essential oil

Tea tree oil

Oncorhynchus mykiss

Rhamdia quelen Reduced liver damage; enhanced antioxidant status.

antimicrobial activity, these constituents chemically interfere with the synthesis or function of vital components of plant pathogens. As a result, both growth and toxin production of these microorganisms are reduced.

Such natural antimicrobial properties make plantderived natural bioactive compounds a great biotechnological tool for the inhibition of fungi growth and, consequently, prevention of mycotoxins production during plant development in the field, storage and food or feed production. In fact, it is well documented that many types of essential oils, plant extracts and isolated compounds obtained from multiple plants and herbs exhibit intense antifungal properties. Furthermore, the use of PFAs as antimicrobials is associated with a low risk of resistance development.

Antioxidant properties

Stressful situations for plants, like fungal attack, may trigger the production of reactive oxygen species (ROS), which activate the reactive antioxidant enzymatic and non-enzymatic responses. The nonenzymatic response is related to the synthesis of several phytochemicals (carotenoids, phenolic acids, flavonoids and others). Likewise, mycotoxins induce oxidative stress via ROS generation, stimulate inflammatory reactions, and induce molecular and cellular lesions in animals. An imbalance between ROS production and the antioxidant defense systems may cause DNA damage, lipid peroxidation, protein damage and cell death. When added to feed, natural antioxidants synthesized by plants have been shown to mitigate and/or prevent the health burden of mycotoxin exposure on animals.

Antioxidants have also been added to commercial feeds to prevent lipid peroxidation and oxidative rancidity during production, processing and storage. Exogenous antioxidants help to preserve the sensory qualities of feed and to prevent the destruction of critical nutrients as pigments and vitamins. The feed/ food industry has become increasingly interested in natural antioxidants because some synthetic antioxidants have shown potential animal and human health hazards. When directly applied to feeding stuff, plant-derived bioactive compounds may therefore improve product shelf life and safety.

Detoxification properties

Several approaches can be taken to minimize mycotoxin contamination in animal feeds, including prevention of fungal growth and mycotoxin formation. Another strategy used to reduce or eliminate mycotoxins from contaminated commodities is the inclusion of feed additives in animal diets. Detoxification seems to be the most attractive way to address the mycotoxin problem.

It may involve physical, chemical or microbiological processes that are applied to detoxify by destroying, modifying or absorbing the toxin. Nonetheless, every treatment has limitations.

The most well-known approach to reduce mycotoxin exposure is to decrease their bioavailability by adding mycotoxin-adsorbing agents to animal feed. Such compounds are able to bind and immobilize mycotoxins in the gastrointestinal tract, thus lowering bioavailability. Despite eliminating the risk of certain mycotoxins successfully, this procedure is not effective for all major mycotoxins in feed commodities. Another alternative is to degrade mycotoxins into non-toxic metabolites by using biotransforming agents such as bacteria or enzymes. Biotransformation has proven to be effective in detoxifying non-absorbable mycotoxins by altering their molecular structure and forming non-toxic metabolites which are then excreted.

Studies have shown that plant-based products with antimicrobial properties may also have decontamination effects. The potential application of plant extracts, essential oils or isolated compounds in mycotoxin detoxification has been explored over the last few years. Cinnamon bark essential oil has been reported to effectively degrade fumonisin. Lemon and grapefruit oils have induced zearalenone degradation, and lemon and palmarosa oils have promoted a reduction in deoxynivalenol content. Aqueous extracts of rosemary, oregano and Corymbia citriodora, also known as lemon eucalyptus, have demonstrated the ability to degrade aflatoxin. In some of these works, the detoxifying effect has been proven by analyzing changes in the molecular structure of mycotoxins.

Such studies evidence the great potential of chemical methods based on aqueous plant extracts and essential oils to degrade mycotoxins in contaminated food and feed products. However, they also report that effectiveness in mycotoxin degradation depends upon factors such as duration of contact between mycotoxin and detoxifying agent, temperature, pH and concentrations of both extract/essential oil and toxin. Although some investigations have demonstrated the efficacy of incorporating plant-based products as alternative food antioxidant and antimicrobial methods, their application as mycotoxin modifiers is limited to in vitro assays.

Benefits to fish health

Although several studies address the benefits of using PFAs as health and growth promoters in fish, there is a paucity of information regarding the advantages of adding these additives to mycotoxincontaminated fish feed. The few (and recent) existing studies are focused on the use of PFAs to mitigate the noxious effects of aflatoxin B1-containing diets (Table 1).

Limitations and perspectives

The future of using plant-derived products in animal feed greatly depends on the information regarding practical plants features, value and chemical structure of the different molecules. The main limitations of using such products, especially in their unprotected form, lie in the instability and the strong aroma and flavor which may restrict applications. Encapsulation technologies can be assessed to provide controlled release of the phytogenic compounds, both in the animal feeding stuffs and gastrointestinal tract, taking into account the possible interactions with foods and/or fish intestinal environments. Additionally, there is a multiplicity of plants and different molecules to be explored as mycotoxin modifiers which may be more stable as well as add less odor and flavor to food. An integrated, multi-stage approach combining myriad actions should be used to tackle the mycotoxin problem. Plant-based natural products can be applied as antifungals, antioxidants and toxin modifiers in different levels of the aquaculture value chain. The combined effects of phytogenic feed additives and other binders or modifiers must also be explored.

References available on request.

More information: Fernando J. Sutili

Researcher, Fish Health and Nutrition Eloaqua, Brazil E: consult@eloaqua.com