There are several factors limiting lipid digestion and absorption. One factor that affects lipid digestion is the age of the animal. These limiting factors provide potential strategies to improve lipid utilisation in monogastric diets. Here we explain what the differences are between the different fat absorbers.
Digestion and absorption of ingested lipids by monogastric animals occurs in three crucial steps (Figure 1):
There are several factors limiting lipid digestion and absorption. One factor that affects lipid digestion is the age of the animal; in young animals (newborn and weaned piglets or broiler chickens of less than 21 d of age) many of the physiological functions required for lipid digestion are immature. These limiting factors provide potential strategies to improve lipid utilisation in monogastric diets. A particular strategy that recently is attracting more attention of nutritionists is the use of exogenous surfactants or often called “emulsifiers”. Lipids need to be emulsified in order to be effectively digested by lipolytic enzymes.
The rate and efficiency of fat absorption is influenced by the average size of the emulsion, nutritional emulsifiers enhance the effect of endogenous bile salts and have the potential to improve lipid utilisation. These effects are more pronounced with less digestible fats and in young animals, whose bile salt production and lipid digestion mechanism are not fully developed.
Different products on the market
There are several exogenous emulsifiers available on the market. According to their characteristics and mode of action they can be classified into three categories: synthetic surfactants (e.g. ethoxylated ricinoleates), lecithins and lysolecithins.
Synthetic surfactants, such as ethoxylated ricinoleates contain a hydrophobic backbone formed by a triglyceride derived from castor oil. In addition the fatty acids in this backbone are ethoxylated to create hydrophylic groups. The degree of this ethoxylation determines its HLBvalue.
Lecithins are present in nature and can also be obtained with the refining of crude (vegetable) oil. In the refining process, the lecithin fraction is separated from the refined oil. Lecithin consists of roughly of 50% phospholipids and the remaining part are triglycerides. Phospholipids are composed of a hydrophilic head and two hydrophobic fatty acid tails (Figure 2). They are amphipathic molecules, having both hydrophilic and hydrophobic characteristics. Due to this property, they are widely used by the food industry as water- in-oil emulsifiers, i.e. to produce margarines.
Lysolecithins are obtained by an enzymatic treatment of lecithins. In this process, the phospholipids are converted into lysophospholipids, or lysolecithins. Lysophospholipids are composed of a hydrophilic head group and one hydrophobic fatty acid tail (Figure 2). Since lysophospholipids have only one fatty acid residue per molecule, they are more hydrophilic than phospholipids and therefore have the increased potential to serve as an oil-in-water emulsifier. Kemin has developed a unique natural biosurfactant highly enriched in lysophospholipids (Lysoforte® Booster Dry) with superior absorption enhancing properties.
The HLB or Hydrophilic-Lipophilic Balance value was developed by Griffin to formulate stable emulsions many decades ago. The HLB value of a non-ionic surfactant describes the molecular weight percentage of the hydrophilic portion of the molecule over the total molecular weight, ranging values from 0 to 20. A specific balance is needed between hydrophilic and lipophilic nature of a molecule to be able to emulsify an oil phase into a continuous water phase.
A high HLB of a given emulsifier reflects its higher hydrophilic characteristic but not necessarily its better surfactant properties under all conditions. The target HLB value depends for example on the properties of the fat used and on how much water or fat is present in the environment. Conditions for lipid digestion in the GIT are oil-in-water, where a limited amount of fat is added to a water rich environment, and most commonly used oils are from vegetable origin. An ideal surfactant to be used in such conditions should have a HLB value ranging from 8 to 12. The HBL value of lysophospholipids contained in Lysoforte (8-12) not only determines its emulsification properties, but also contributes to the stability of emulsion (Figure 3).
The HLB value of bile salts is 18.When bile salts act isolated in an oil-in-water environment they are not able to form emulsions because they are too hydrophilic and behave like detergents. On the other hand, when bile salts are mixed with biosurfactants like Lysoforte Booster Dry they are able to form much more stable emulsions.
Both synthetic surfactants and lecithin based products, when supplemented to animal feed, have the capacity to emulsify the fat of the feed in the stomach (Table 1), leading to a reduced size of fat droplets.
At the small intestine, the reduced emulsion droplet created by the highly functional lysophospholipids contained in Lysoforte® Booster Dry results in an increased available surface for bile salts and lipases to interact. Differently from lysophospholipids, due to their very high hydrophilic nature and relatively large molecular size, ricinoleate based surfactants have the tendency to enter in competition with the bile salts for the available surface of the fat droplet (steric hindrance, Figure 1). As a result, bile salts are not able to prepare the surface of the lipid droplet for the lipases to attach. Consequently, the smaller fat droplet size produced in the stomach does not result in a proportionally improved lipid hydrolysis and micelle formation. The particular shape of lysophospholipids, due to the cleaving of one of the hydrophobic fatty acid tails (Figure 2), makes them much more efficient than lecithin in the emulsification and the subsequent fat hydrolysis (Figure 4).
After lipid hydrolysis, the free fatty acids, monoglycerides, bile salts and lysophospolipids are incorporated into the micelles. Lysophospholipids reduce the size of the micelles and stabilize them to a much higher extent compared to phospholipids (lecithins). Lysophospholipids are naturally part of the micelles and thus are absorbed together with the fat hydrolysis products by the intestinal epithelium (Figure 5). On the other hand, synthetic emulsifiers, due to their shape, size and very high hydrophilic nature, cannot be incorporated in the micelles having no effect on improving the absorption of their components.
Both (lyso)phospholipids and synthetic surfactants (such as ethoxylated ricenoleates) are able to improve the emulsification of triglycerides in the stomach. Additionally Lysoforte goes three steps beyond traditional emulsifiers:
Synthetic emulsifiers are widely used for emulsifying or other surfactant properties. Synthetic emulsifiers are technological feed additives aiming to improve water retention of the feed and yields at the feed mill. They contain perfect surfactant properties, but are not able to improve the crucial steps in lipid digestion as for this lysolecithines are needed. Compared to lysolecithins, lecithins have a much more limited capacity to improve all necessary steps of lipid digestion and absorption (Table 1). The lipid digestion process occurs in oil-in-water conditions, while due to their structure, lecithins have water-in-oil emulsifying properties.
Kemin is the original pioneer in absorption enhancers and Lysoforte not only improves the digestibility of poor quality fats and oils, but also is able to improve the digestibility on the good quality lipids, high in ME fats/oils. The natural biosurfactant Lysoforte Booster Dry has been successfully tested in several animal species (broilers, layers, turkeys, pigs and fish) and conditions over the last 20 years, producing as a result a vast amount of scientific and practical information. Lysoforte is a flexible tool and can be used to achieve many different goals. It has been successfully tested and applied in monogastric nutrition to improve:
Nowadays animal nutrition requires efficient solutions and Lysoforte is the flexible tool to meet these needs.