Improving fat digestibility with emulsifiers

By Marc Rovers, Orffa/Excentials, 
the Netherlands


The terms fat, oil or lipid refer to triglycerides of several profiles of fatty acids. Fatty acids that are not bound to other organic components as glycerol are the so-called free fatty acids. Lipids constitute the main energy source for animals and they have the highest caloric value among all the nutrients. The amount of energy that an animal can obtain from the dietary fat depends on the fat digestibility. Figure 1 illustrates the fat digestion in a body. A higher digestibility will result in more available energy. The digestibility of fat by animals is related to different characteristics of the fat and the absolute amount of fat added to the diet. Factors such as animal age also influence the digestibility. Young birds have a low level of natural lipase production and a low rate of bile salt production. Fortunately, the limited fat digestion can be enhanced by adding emulsifiers to the diet.

Fat digestion occurs in a few steps.
Initially, the large fat globules are emulsified in the watery environment of the gut aided by peristaltic movement. Normally fat and water do not mix and therefore bile salts assist in this mixing process as a natural emulsifier. Smaller fat droplets are formed to increase the contact surface for the enzyme lipase. This enzyme is produced by the pancreas and breaks down the fat. Fats and oils are esters of three fatty acids and glycerol. The fatty acids are released (hydrolysed) from the glycerol by lipase. This results in two fatty acids and a monoglyceride. The next step is the formation of micelles. Micelles are water soluble aggregates of lipid molecules containing both polar and non-polar groups. Molecules are grouped in the micelles in such a way that the polar groups are on the outside in contact with the aqueous phase, while non-polar parts form the inner lipid core of the micelles. Bile salts and monoglycerides aid as emulsifiers in the formation of micelles. When the micelles come into contact with the micro 
villous membrane they are disrupted and the fatty acids can be absorbed by the lipophilic cell membrane.

Nutritional emulsifiers

Bile salts are natural emulsifiers. The monoglycerides that are formed after hydrolysis of the fat also act as emulsifiers. Nevertheless, the capacity of these natural emulsifiers can be a constraint for fat digestion. Young animals have a limited production of bile salts and therefore fat digestibility is premature in the early stage of life. On the other hand, the characteristics of dietary fat can restrict the digestibility. Fatty acid mixtures with high amounts of free fatty acids lack the formation of monoglycerides and therefore have a lower emulsifying capacity. Long chain unsaturated fatty acids and monoglycerides form micelles promptly, whereas saturated fatty acids have lower ability to form micelles because of the low polarity. These characteristics of the fat explain the difference in digestibility. In general, saturated fatty acids, mostly found in animal fat, are digested less easily compared to unsaturated fatty acids, like in vegetable fat. High levels of free fatty acids also limit the digestibility. Exogenous nutritional emulsifiers can assist in the digestibility. Obviously, the positive effect of adding such emulsifiers is more pronounced for lower digestible fats than for very high digestible fats. The effect will also be more pronounced at higher levels of added fat. Nevertheless, even with high digestible fats, positive effects have been observed.

HLB balance

An emulsifier is a molecule with a water soluble (hydrophilic) part and a fat soluble (lipophilic) part. The combination of these two characteristics in one molecule gives it the unique property that the emulsifier can dissolve as well in fat, as in water, and can aid in mixing the two fractions. Different types of emulsifiers are commercially available. When choosing an emulsifier the Hydrophilic-Lipophilic Balance (HLB) is a key indicator, showing how fat or water soluble a product is, 
ranging from 0 to 20 ( Figure 2 ). The lower the HLB, the more lipophilic or fat soluble the emulsifier becomes. On the other hand, the higher the HLB, the more water soluble or hydrophilic the emulsifier will be. Ideally, the emulsifier should be soluble in the continuous phase as the Bancroft rule states. When a small amount of water is mixed into a fat-rich environment, a lower HLB is advised (fat 
soluble). If a small amount of fat is mixed into an aqueous environment, an emulsifier with a higher HLB is advised (water soluble). In the case of a nutritional emulsifier a limited amount of fat is added to the watery environment of the gut. As birds consume 1.5 to 2 times more water than feed and the feed contains only a small amount of fat, the water amount is much higher than the fat amount in the intestine. In this case a high HLB is more suitable.

Trials with broiler diets

Several experiments were carried out to demonstrate the effect of emulsifiers on fat digestibility in broilers. In a first experiment four different nutritional emulsifiers with relatively high HLB values were added to the diet (dosing 250 g/t). All four emulsifiers increased fat and energy digestibility and this resulted in a higher AMEn value of the diet. Emulsifier B ( Excential Energy Plus ) had the highest fat digestibility and an energy increase of 137 kcal ( Figure 3 ).The second experiment tested whether it was possible to formulate a diet with a lower energy content and compensate with an effective emulsifier. Two diets with different fat composition were compared, one with a conventional fat composition, and another with a high level of saturated fatty acids and free fatty acids. The diets with reduced energy and addition of the emulsifier performed at the same level as the control diets. This indicates that the addition of an effective emulsifier was able to compensate for a 5.3% lower energy content ( Figure 4).

Save energy and cost

The addition of an effective emulsifier to a diet can compensate for a reduction in dietary energy. What does this mean for farmers in practice? If a diet can be formulated with a lower energy content, this means less addition of expensive fats and oils and as a result a lower cost price. The effect on cost price depends on nutritional constraints in the formula and on raw material prices, next to regional variation and fluctuation over time. To give an insight in the magnitude of the effect, a typical Northern European broiler diet was 
formulated with different energy levels. By lowering the basal diet from 3,100 kcal to 3,000 kcal, the oil and fat 
contents were limited, leading to a cost reduction of more than €10 per tonne (Figure 5 ).