Emulsifiers in Poultry and Swine: Roles and Functions

In Ho Kim, Dankook University, Republic of Korea

The major cost of feed formulation in Korea stems from energy ingredients. Therefore, improving the energy efficiency of these raw materials is economically critical. Fats serve as an important energy source in animal diets due to their high energy density. The amount of energy animals can derive from dietary fats largely depends on fat digestibility. In the absence of emulsifying molecules such as bile acids, fat digestibility declines substantially.

Extensive literature has demonstrated that young animals face physiological limitations in fat absorption, owing to low endogenous lipase secretion and restricted bile acid output. Incomplete fat digestion raises the requirement for energy sources, which in turn pushes up feed costs. (Figure caption: Oil phase + aqueous phase → stirring + emulsifier → formation of oil-in-water emulsion)

This research focuses on enhancing fat digestibility to address low energy utilization efficiency in monogastric animals. Emulsifiers stabilize mixtures of two immiscible substances (oil and water) and prevent coalescence of droplets in the dispersed phase. Lipids must therefore undergo emulsification first. The formation of fine emulsified fat droplets enlarges the surface area available for pancreatic lipase, facilitating fat breakdown. Natural or synthetic emulsifiers can be applied to improve fat digestibility and boost energy efficiency, thereby reducing feed costs.

Emulsifiers promote lipid digestion and absorption by finely dispersing oil droplets within the emulsion. Emulsion types can be selected systematically based on the hydrophilic–lipophilic balance (HLB), and properly blended emulsifiers can enhance emulsion stability. Emulsifiers can penetrate tiny gaps within entangled protein layers to reach the protein-stabilized interface, exerting surface pressure and forming an emulsifier-enriched region at the interface. An emulsifier molecule consists of a hydrophilic head and a hydrophobic tail. The hydrophobic tail orients toward the oil phase, while the hydrophilic head faces the aqueous phase.

Effects of Emulsifiers on Production Performance and Nutrient Digestibility in Poultry and Pigs

Natural emulsifiers are produced endogenously in animals (e.g., bile acids and phospholipids) or derived from plants (e.g., soybean lecithin). A wide range of emulsifiers are currently applied in diets for poultry and pigs. In an early study, Jin et al. (1998) reported that weaned piglets fed a basal diet with tallow as the energy source and supplemented with lecithin exhibited greater average daily gain (ADG), average daily feed intake (ADFI), and gain-to-feed ratio (G:F) than those fed the unsupplemented basal diet. In addition, Jones et al. (1992) found that adding emulsifiers such as lecithin or lysophosphatidylcholine to nursery pig diets containing soybean oil or tallow as energy sources improved fat digestibility, whereas no such effect was observed in diets with lard. Furthermore, Kim et al. (2008) demonstrated that lecithin supplementation for finishing pigs increased ADG and reduced feed conversion ratio (FCR). Xing et al. (2004) reported that lysophospholipid (LPL) supplementation in diets containing 5% lard improved ADG from day 15 to 35 and over the whole experimental period (day 0 to 35). The positive effects on growth performance may arise from improved palatability by dietary LPL or lecithin supplementation, which increases feed intake and energy intake (Overland and Sundstol, 1995). For sows, supplementation with 3% LPL in the diet reduced body weight loss and backfat loss, while improving apparent nutrient digestibility and nutrient concentrations in milk (Zhao et al., 2017). Emulsifiers may also facilitate the absorption of other nutrients such as protein. According to Zhao et al. (2015), pigs fed LPL-supplemented diets had higher total tract apparent digestibility (ATTD) of dry matter (DM), gross energy (GE), and ether extract in the first two weeks and the subsequent three weeks post-weaning. Jin et al. (1998) also concluded that dietary lecithin emulsifier improved the ATTD of DM, GE and nitrogen (N) in weaned piglets. Similar results were observed in growing pigs supplemented with LPL (Dierick and Decuypere, 2004). Overland et al. (1993a) noted that soybean oil supplementation improved the ATTD of DM, GE, ether extract and crude protein (CP). Conversely, in weaned piglets, supplementation with lecithin (Overland and Sundstol, 1995) or LPL (Xing et al., 2004) resulted in a linear decrease in ATTD of DM, CP or GE. Soares and Lopez-Bote (2002) found no evidence that dietary LPL supplementation affected the digestibility of DM, CP or crude fiber in weaned piglets during the first two weeks or the following two weeks after weaning. Moreover, according to Jones et al. (1992), ADG increased significantly from day 0 to 7 post-weaning when tallow and lecithin were used, but the beneficial effects appeared to gradually diminish as pigs approached day 35 post-weaning. This trend indicates that the growth-promoting benefits weaken as pigs grow older. Therefore, the efficacy of emulsifiers is affected by animal age and the type of fat included in the diet.

Tenderness is the most important quality attribute of meat. Hence, improving pork tenderness is critical to enhancing consumer satisfaction. It has been reported that dietary lecithin supplementation (0, 0.4%, 2% and 8%) improved chewiness and dressing percentage and reduced pork color values (Akit et al., 2014). The improved chewiness is attributed to lower collagen content induced by dietary emulsifier supplementation. In addition, the 1.5% and 7.5% lecithin treatments reduced hardness and chewiness of longissimus thoracis muscle, while no effect was seen in the 0.3% lecithin group. Furthermore, weaned piglets fed lecithin-supplemented basal diets with lard as the energy source had lower serum cholesterol concentrations than those fed diets based on tallow. On the other hand, pigs fed lard plus lysophosphatidylcholine had higher cholesterol levels than those fed tallow plus lysophosphatidylcholine (Jones et al., 1992). This indicates an interaction between emulsifiers and energy sources on total cholesterol concentration. Concentrations of high-density lipoprotein (HDL) or triglycerides were not affected by dietary fat sources (soybean oil, poultry fat, a 50:50 blend of soybean oil and poultry fat) or emulsifier addition (Guerreiro Neto et al., 2011). Zhao et al. (2015) found that supplementation with 0.05% and 0.10% LPL exerted no obvious effects on LDL cholesterol. Fat source and emulsifier type may play important roles in modulating serum lipid profiles in animals.