Abstract

Keywords

Polyphenols, Essential Oils, Tannins, antimicrobial, growth promoting, antioxidative

Co-Author

Rainer Aschenbroich and Lea Hesselmann

Introduction

Unlike most animals, plants do not have the ability to escape potential predators by running away. To secure the survival of their species, plants have evolved multiple mechanisms to defend themselves against potential threats.
Most of these mechanisms are based on the synthesis of a combination of compounds with specific biological activities, which have been recognized and used for appetizing, digestive or therapeutic purposes for many centuries in humans and animals.

In contrast to so called primary plant compounds that are of importance for growth and reproduction of a plant like carbohydrates, proteins and vitamins (Ehrlinger, 2007), secondary plant compounds are not directly involved in the general energy and nutrient metabolism but offer a benefit for the plants in the natural selection process. Some compounds, for example emit odors to attract pollinating insects or as defensive mechanism to protect against pathogens or predatory herbivores thus preserving the individual plant and the species respectively (Westendarp, 2007).

The amount and the composition of secondary plant compounds is determined by many different factors like genetic configuration and growth stage of the plant as well as external influences like climate, weather and soil conditions (Westendarp, 2007).

Between the different active substances mutual interactions can be observed. The special combinations determine the intensity of the total impact and it is assumed that substances with even very low concentrations can be significantly involved in the mode of action (Westendarp, 2007).

This leads to the conclusion that isolated or chemically synthesized single compounds cannot have the same activity as a mix of plant components acting synergistically (Heinzl, 2010). Safrol for example as single substance is very toxic for liver and kidney and furthermore is assumed to be carcinogenic. Consumed as an ingredient of black pepper or nutmeg however, such toxic effects are not observed.

Secondary plant compounds are of wide structural variety. Most of the approximately 100,000 known secondary plant compounds are believed to be involved in the plant defense and reproduction system. This diversity of ingredients also offers a multimodal use in animal nutrition.

It has to be considered that a specific and effective application can only be implemented if there is specific knowledge about their composition and mode of action (Westendarp, 2007).

Classification of secondary plant compounds:

Secondary plant compounds can be categorized in different ways. They are either distinguished based on their active groups, chemical characteristics, commonalities in biosynthesis or impact and purpose of use (Westendarp, 2007).

Phenolic or polyphenolic substances

Phenolic or polyphenolic compounds comprise a large family with over 4,000 diverse compounds widely distributed in plants and their fruits.

They are produced by the plant for coloring, growth, reproduction and as defense mechanisms. They are formed by several hydroxyls connected to one or more aromatic rings and possess a high antioxidant capacity. They can be found in fruits such as apples or cherries, in vegetables such as broccoli or onions, but are also contained in red wine, chocolate or green tea. Depending on their natural function in the plant they can act in an antimicrobial and antifungicidal or antiparasitic way in the gastrointestinal tract of the animal (Giannenas, 2008).

Essential oils

The ISO standard 9235 (1997) defines “essential oils” as products, which are extracted from plant material (one single species) by either distillation with steam (in case of e.g. menthol), by mechanical treatment at room temperature (e.g. cold pressed as orange oil or lemon oil) or by dry distillation.

They are mixtures of volatile, liquid, lipophilic compounds. They can be synthesized in each part of the plant. Some plants have the ability to build essential oils with different compositions in different parts of the plant and in practice most of them are extracted by steam distillation.

Approximately 3,000 compounds have been isolated and analysed from essential oils. Whilst in some essential oil types only a few components are present ore one compound dominates, other essential oils can be composed of up to 100 components (Wald, 2003).

Due to that diversity it is difficult to determine the proportional efficacy of single compounds in often complex mixtures (Westendarp, 2007). But more and more scientific studies demonstrate a wide antimicrobial activity of many essential oils.

Tanning agents

Tannins are special types of phenols. They can be found in variable concentrations in different parts of a plant. Since they interact with proteins on mucous membranes they are traditionally used in cases of unspecific diarrheas, inflammation of the oral cavity and the pharynx as well as to cure slight skin lesions. Additionally tanning agents are radical scavengers and act as antioxidants. Furthermore they have antimicrobial and antiparasitic effects.

Bitter substances cannot be allocated to a chemically consistent group of elements. The commonalities in this group are based on their bitter flavor. With oral administration the production of saliva and anapepsia is stimulated by the excitation of the taste buds.

Pungent substances cannot be assigned to chemical group either. Besides a stimulation of saliva and anapepsia production the oral administration causes an enhancement of gut motility. Other effects are enhancement of blood circulation, antiemetic, antimicrobial, germicidal and insecticidal (Westendarp, 2007).

Alkaloids can have a direct impact on the nervous system, by agonistic or antagonistic binding to neurotransmitter receptors. Furthermore they can inhibit metabolic enzymes or have interactions with intracellular proteins. Alkaloids are mainly used as analgesics, sedatives or against diarrhea.

Saponins can be found in about 75 % of all plants and the individual forms vary greatly. They can reduce cholesterol levels, act fungicidally and some types show an immune stimulating effect (Westendarp, 2007; Heinzl, 2010). Saponins are also used for their reducing effects on ammonia emissions in animal feeding, by inhibition of urease activity (Veit et al., 2011).

Mode of action

Secondary plant compounds not only exert one specific mode of action. For most SPCs a broad range of efficacy has been demonstrated. In poultry production, some of the most important beneficial attributes are mentioned below.

Stimulation of digestion

Stimulation of the sensor cells in the gastrointestinal tract. This results in higher concentration of calcium ions followed by an increased release of Serotonin. This chemical messenger activates the muscles of the digestive tract and the secretion of digestive juices, which as a consequence improves resorption of nutrients (Braun et al., 2007).

Antimicrobial interaction on bacterial cell integrity

a) Through interactions with transmembrane proteins secondary plant compounds can lead to changes in the transport capacity of sodium and potassium ions, which diminishes the membrane potential across the bacterial cell membrane.

b) Through lipophilic interactions, secondary plant compounds can increase the permeability of the cell membrane, disturbing the balance of ion concentrations and thus leading to an impairment of osmotic pressure regulation.

c) Through uncoupling of the electron transport chain, secondary plant compounds can impair ATP generation and thus energy production in the bacterial cell.

Increase of antioxidative activity

The antioxidant activity is related to the capacity of polyphenols to act as metal-chelators, scavengers for superoxide or hydroxyl radicals, hydrogen donators and inhibitors of the enzymatic systems responsible for initiating oxidation reactions (Mielnik et al., 2008; Gobert et al., 2010; Sayago-Ayerdi et al., 2009). Higher oxidation is an index for lower meat quality. Numerous studies have pointed out the positive effect of secondary plant compounds on meat quality (Viuda-Martos et al., 2010; Janz et al., 2007; Viuda-Martos et al., 2010; Al-Mamary et al., 2002; Russo et al., 2000). Secondary plant compounds especially polyphenols and flavonoids generate a positive effect on meat quality and thus increase shelf-life by:

Reduction of lipid oxidation and microbial growth in meat during storage

Delayed degradation of vitamin E in meat

Improved meat color conservation during storage

Moderation of aldehydes and alcohols related to off-flavor in meat

Synergistic effects

Between the different components synergistic interactions, leading to an increase in the efficacy of the single active compounds have been observed in numerous studies (Figure 1). Therefore the type of combination determines the intensity of the total effect. In such a composition also substances present in very low concentrations can significantly contribute to the overall mode of action (Heinzl, 2010). Other important factors, influencing the efficacy of single active compounds and their combinations are determined by the uptake rate, metabolisation and their availability at the preferred site of action in the organism (Westendarp, 2007).

Trials, demonstrating the in vivo efficacy of special combinations

Animal trials were conducted with ACTIVO, a product line containing several secondary plant compounds acting in a synergistic way. The trial parameters shown below are representative for the three main modes of action.

1. Activation of digestion:

The trial was conducted on a farm in the Czech Republic with 189,300 (Control group) and 62,300 (Trial group) Ross 308 chickens of mixed sex. The control group was fed with standard feed + 150 g / ton of a competitive product, the trial group received standard feed + 100 g of ACTIVO / ton (Figure 2).



Outcome: Feed conversion rate of animals fed ACTIVO significantly improves when compared to a competitor product

2. Antimicrobial efficacy compared to antibiotic growth promoters

In this trial commonly used feeding programs in Brazil applying AGP’s were compared to a diet containing Activo based on secondary plant compounds. For this trial 1,120 Cobb male chicks were divided into 7 different groups, which were fed as mentioned in table 1. Experimental diets were formulated with requirement levels 10% lower than recommended. The parameters “Feed intake”, “Growth”, “FCR”, “Average final weight”, “Mortality” and “FEF Index” were evaluated during 45 days (Figure 3).



The trial was conducted in order to show the positive effects of secondary plant compounds in comparison to antibiotic growth promoters especially under bad hygienic conditions. At days 11, 14, 17, and 24 birds were challenged with a solution containing strained dirty (contaminated) bed litter and water in a proportion of 15 g/L. Birds were allotted to boxes containing reused wood shavings and facilities were not cleaned at the beginning or during the experimental period as well.

Outcome: Activo shows similar results as antimicrobial growth promoters in terms of animal performance, thus indicating good animal health. (Trial conducted by Federal University of Viçosa, Viçosa, Minas Gerais, Brazil)

3. Increase of antioxidative activities to extend shelf life of meat

640 male animals were divided into 4 groups, each group with 8 replicates (20 animals / pen). The animals were fed as shown in the following table.



After slaughter, breast samples were frozen at -20°C for 30 days. Samples were then thawed to examine lipid oxidation level, by measuring the Malonedialdehyde content (Figure 4). Malonedialdehyde (* MDA) is generated from reactive oxygen species (ROS), and as such is assayed in vivo as a bio-marker of oxidative stress (Stancliffe et al., 2011).

Outcome: ACTIVO significantly decreases the level of lipid oxidation during meat storage. Trial conducted by Federal University of Viçosa, Viçosa, Minas Gerais, Brazil.