Emulsifiers in Poultry Nutrition –
An indispensable feed additive
Dr. Ibne Ali,
M.V.Sc – IVRI
Abstract: Fat
feeding in poultry is greatly overlooked in spite of having its high nutrient
value not only as a source of energy but its role in metabolic and immune
system functions. Fat provides more than twice energy than either protein or
carbohydrates on equal weight basis. Fat also provides essential fatty acids
which have crucial importance in making prostaglandins which help in combating
infections. Absorption of fat soluble vitamins is also linked to fat in diet.
If fat is reduce in diet their absorption is also get affected. Fat digestion
is done by lipase and co lipase but they cannot work unless fat is get
emulsified. This emulsification is performed by emulsifiers. Poultry produce
emulsifier in the form of bile but it is in insufficient quantity so addition
of emulsifier from outside is become obligatory in poultry feed. These
emulsifiers are phospholipids. Lecithin and lysolecithin are vastly used and
one of the most efficient emulsifier. Proper ratio of lecithin and lysolecithin
is needed for its efficient function as an emulsifier. This ratio is measured
by HLB value parameter and it should lie between 8 – 16 units, which help in
forming oil in water emulsion. It is one of the turning point innovation in
poultry feed industry to reap maximum profits.
Key words: Emulsifier, prostaglandins,
lipase, lecithin, lysolecithin, HLB, CMC, phospholipid
Introduction
Chickens
require energy and a number of essential nutrients, including amino acids,
minerals and vitamins, for maintenance, growth and egg production. Fat is
usually included in diet formulations to meet the high energy requirements of
broiler chickens, as the energy value of fat is at least twice as high as those
of carbohydrates and protein. Other benefits of adding fats include improved
palatability, improved absorption of fat-soluble vitamins, dust control in feed
mills and provides essential fatty acids for immune system potentiation.
Furthermore, fat slows down the rate of food passage through the digestive
tract, allowing more time for better digestion and absorption of nutrients.
Supply of
energy represents the major cost in feed formulations. Due to the recent
increases in the price of cereals, there is increasing interest in exploring
ways to improve the energy value of fats. Therefore, there is a need for
greater understanding of the digestion and absorption of fats in poultry.
It is accepted
that the small intestine is the major site of digestion and absorption of fat;
usually it takes place in jejunum and ileum. There is a continuous secretion of
endogenous lipids, mainly in the form of bile, into the lumen of the intestinal
tract. These endogenous emulsifiers are not much efficient in the digestion of
fat and importantly when we increase fat content in poultry diets. In that
situation these dietary lipids get partially digested and less absorption is
seen. The unabsorbed fraction passing beyond the ileum is considered a loss to
the animal. Recently, a detailed study on endogenous losses of fat and fatty
acids in chickens have been carried out at Massey University, New Zealand
(Tancharoenrat, 2102). It is well documented that the digestion and absorption of fat in newly hatched chicks is poor due
to the immaturity of physiological functions. In particular, the secretion of
lipase and bile seems to be first limiting during the first week of life. The
ability to digest and absorb dietary fat develops after the first week of life.
Further in layers where fatty acids are required to deposit into the egg yolk
it become very crucial to lose fat of the diet.
Non-starch polysaccharides, such as
arabinoxylans and β-glucans, increase the digesta viscosity and depress the digestibility of nutrients
by impeding the diffusion of digestive enzymes and substrates, and contact
between nutrients and absorption sites on the intestinal mucosa. Available data
suggest that the digestion of fat is
affected more than that of other nutrients by NSP and that the digestion of
saturated fatty acids is affected more than that of unsaturated fatty acids.
Poor digestion of saturated fatty acids was attributed to intestinal viscosity
which may lead to reduced gut motility and, decreased rate of diffusion
and transportation of emulsion droplets, lipase, mixed micelles, bile salts and
fatty acids in the gut lumen. NSP attributes to poor emulsification of fats in
the diets. Furthermore, saturated fatty acids are non-polar and do not form
mixed micelles spontaneously, and thus are poorly emulsified. While the
interaction between viscous cereals and dietary fat sources is well documented,
this gave leading insights to the poor fat digestion.
So it is
apparently clear from the discussion that we cannot afford to ignore the fat inclusion,
digestion and absorption. In this discussion we have also seen that variety of
nutrients which belongs to the chemical i.e. lipid are essential for proper
functioning of the body.
Fat is much more important than source of energy;
there are other issues which need to focus…
Fat is not
just a source of energy but much more than energy, it helps in digestion and
absorption of fat soluble vitamins. Poor fat digestion may lead to infection
outbreaks due to poor immunity that results from deficiency of anti-infection
vitamin A. Rickets is observed as a two prong effect, first as decreased
digestion and absorption of vitamin D and secondly, when free fatty cant able
to remain in micelles due insufficient bile secretion in concerned birds,
those free fatty acid molecules binds with ionic calcium and makes them
unavailable. Oxidative stress is also lamentable because of poor availability
and absorption of vitamin E.
Indispensable role of vitamin E in combating
free radicles.
What are
free radicle -
Highly reactive molecules containing one or more unpaired electrons and can
exist independently (e.g. superoxide, O*2 -, and hydroxyl, OH*) they try to
achieve stability by losing or gaining electron, which means it destroy other
molecules. Free radicles play an essential role in the extracellular killing
of microorganisms by activated phagocytes.
All
molecules are susceptible to be destroyed by free radicles but lipids are
more susceptible. Cell membranes are important targets as they are made of
polyunsaturated fatty acids. In the core of the issue, Lipids are the most
susceptible; oxidative destruction of polyunsaturated fatty acids can be extremely
damaging, since it proceeds as a self-perpetuating chain reaction.
The more active cells, such as muscle
cells, are at greatest risk of damage because they depend on the
utilization of lipids as energy sources.
To
maintain cell integrity the animal’s cells require protection mechanisms and
these are provided by the antioxidant system. The initial line of defense is
by the enzymes superoxide dismutase (containing copper), glutathione
peroxidases (containing selenium) and catalase.
Antioxidants
break the chain reaction by scavenging
peroxyl radicals and thus interfere with the propagation steps in the
lipid peroxidation process. Vitamin E
is the main antioxidant but the carotenoids, vitamin A and vitamin C are
also involved. In mammalian cells vitamin E is located in the mitochondria
and endothelial reticulum. Vitamin E is one of the most important antioxidant
which present in cell membrane (mostly antioxidants present in cytosol) and
prevent cell damage.
Vitamin D3
Decrease
in fat digestion also lower down immunity due decrease in inflammatory
responses against infections. Heterophils in blood releases cytokines like
prostaglandins and thomboxanes are mainly responsible for fighting against
infections through inflammation. Arachidonic acid which derived from linoleic
acid form cytokines like prostaglandins and prostacyclins together these
molecules are called as eicosanoids which mediates inflammatory reactions in
the body. Deficiency of linoleic acid in the diet compel the heterophils to
destroy their own cell membranes because phospholipids in cell membrane would
become the source of linoleic acid, this ultimately decreases the efficiency of
immune cells to invade infectious agents.
We know
poultry is remain under continues stress which is known as metabolic and
production stress. During stress adrenaline and corticosteroids secreted from
adrenal gland trigger gluconeogenesis which causes generation of glucose from
non-polysaccharide source i.e. glycogen. Its first preference is fat and if
fat is not available than protein. So, it would be much more difficult to
maintain body growth in stressful condition without having sufficient fat
because fat is not available and body forces to mobilize body protein for
glucose generation.
In
conclusion dietary inclusion of fat is very desirable to include in poultry
diet not just to add extra energy but improve overall performance of the bird
in the conditions of production stress.
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Fat digestion physiology in poultry
No fat can be
digested unless it is emulsified by an emulsifier. In a whole process of fat
digestion two main factors work in complementation i.e. lipase with colipase (lipase is non-functional without co-lipase)
and emulsifier. Emulsifiers are required to break down the fat droplets into
smaller particle so that lipase can act on triglycerides easily and
efficiently. Lipase cannot be effective on large lipid droplets. So we need
emulsification of fat prior to its digestion, which means we made fat water
soluble which is otherwise insoluble in water. To make fat soluble in water
emulsifiers are needed. Efficiency of emulsifiers is main dictating factor
which determines the proficiency of fat digestion. This efficiency is
determined by CMC value of emulsifier. CMC value is defined as the number of
emulsifier molecules required to make emulsion droplet or micelle. Lipase
activity is sufficient in the digestive tract however insufficient bile causes
decrease fat emulsification and hence fat digestion. But this mechanism is not
so easy to understand because surface tension of water is a barrier for dissolution
of fat in water. Emulsifier (also known as surfactants) decreases this surface
tension upto the value of fat so that fat start dissolving in water. Also, at
this value micelle formation starts which are the real structures for fat
absorption. Structure of these micelles is simple, it is spherical molecule and
shell of this sphere is made of hydrophilic (water loving) polar groups like
phosphate, choline or ethanolamine etc. and inner part is made of hydrophobic
(water repelling) molecules mainly fatty acid chains. Inside these micelles fat
molecules resides which will undergoes subsequent absorption. Size of micelle
is important factor in the digestion therefore, it had been identified
previously that the CMC value have marked influence on the size of the micelle,
lower CMC value leads to smaller micelle (Belitz’s - Food Chemistry 4th
edition).
Figure
shows structure of micelle which is spherical in shape however other shapes of
micelles are also seen like hexagonal, lamellar, cubic etc. it all depends upon
properties of emulsifiers.
Emulsifiers and their roles
From
above discussion it has been clear that why fat is important in poultry
nutrition and how we can make it available for growing poultry birds. Dietary
supplementation of Phospholipids (PLs) has proven to be effective in improving
fat digestion and nutrient utilization, and consequently in improving growth
performance, particularly in broilers and layers. PLs are recommended to be
supplemented into feeds for chicks, containing a higher level of feed
fats/oils, as well as a higher level of saturated fats.
Emulsifiers
are classified by their hydrophilic/lipophilic
balance (HLB). This means the balance between their activity in the two
media- water and fat. It is a scale which varies from 0 to 20. An emulsifier
has, symbolically speaking, a hydrophobic tail and hydrophilic head. The tail
can vary a lot in size and is the main parameter which influences the
molecule’s activity. Phospholipids are made of 2 parts, one part is polar group
and another is non-polar group. The balance of polarity and non-polarity
dictates its usefulness as emulsifier. To make oil in water emulsion (which is
required as it is seen in poultry intestine) we need more hydrophilicity and less
hydrophobicity. It means HLB value should be more than 8 on the scale of 0 to
20. Normal lecithin based phospholipids provides HLB value of 5 which is not
sufficient to be a good emulsifier but proper addition of lysolecithin
increases its HLB value upto needed level. Ratio of lecithin and lysolecithin
is important in determining the stability of micelles and hence its absorption.
Lysolecithin is derivative of lecithin and obtained by enzymatic digestion of
lecithin through enzyme phospholipase A₁
(same enzyme found in snake poison).
Figure showing structure of
lecithin (having 2 tails) on left and lysolecithin (having 1 tail) on right
Lecithin and Lysolecithin
Lecithin
is widely used phospholipids derived naturally from eggs or soy bean and commercially
used as emulsifiers in various fields, like cosmetics, food industry and
poultry feed. Soy lecithin is preferred due to its low price and it is
produced as by product of edible oil processing from water degumming step. Lecithin
is not a single phospholipid but mixture of various PLs. As per Wu and Wang (2009) soy lecithin
contained 18% PC, 14% PE, 9% PI, 2% PA, 2% other minor phospholipids, 11%
glycolipids, 5% sugar complex, and 37% neutral lipid. Linoleic acid was the predominant
fatty acid for PC, PE, and PA. Partial enzymatic hydrolysis of purified
lecithin led to phospholipids profile changes. After hydrolysis, even at 10
minutes hydrolysis time, lysophospholipids are produced. Increasing
hydrolysis time increased lysophospholipids (lysolecithin) content in
lecithin. Partial hydrolysis makes lecithin more hydrophilic that had higher
HLB value.
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Conclusion
In
changing scenario of poultry production technology we have to focus on
efficient utilization of resources to gain maximum profits. In poultry
industry, if look at it closely we can see that industry’s prime focus is on
reducing feed wastage by improving digestion. But at the same time absorption
of digested nutrient should also need to address properly otherwise good
digestion does not make any sense. Since inception of commercial poultry
industry many innovations have taken place which change and gives new thrust
for production system and help poultry farmers to reap higher profits, one such
innovation is use of emulsifier in poultry feed. Negligence of fat feeding, its
digestion and absorption could have serious impact on FCR and overall
production in long run. We center our efforts on this issue and formulate high
grade poultry feed emulsifier, which is having high HLB value and low CMC value
for better absorption of fat.
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