Emulsifiers in Poultry Nutrition – An indispensable feed additive
Dr. Ibne Ali, M.V.Sc – IVRI
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.
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 thedigestion 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. |
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. lipasewith 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. |
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.
