Why Emulsification is Needed: Role of Surfactants / Emulsifiers

Introduction:

“In poultry nutrition, emulsifiers are a type of surfactant used primarily to aid fat digestion by forming stable emulsions in the gut.”

Understanding Emulsifiers:

• Hydrophilic (polar) head: water-soluble
• Hydrophobic (non-polar) tail: oil-soluble

Mechanism of Action:

Key Points on Digestion of Lipids in Poultry:

• Initiation of Digestion: Triglyceride breakdown begins in the gizzard, where mechanical breakdown and mixing occur. Approximately 75% of fat digestion occurs in the jejunum.
• Emulsification Process: Pepsin activity in the gizzard initiates emulsification, aided by the acidic environment and churning action.
• Gut Reflexes: Reverse peristaltic movement increases feed retention time, aiding in digestion.
• Introduction of Bile Salts: Bile salts and monoglycerides from the duodenum and jejunum start the emulsification process. Bile salts are largely composed of pigments, water, sodium salts, phospholipids, cholesterol, and amino acids. Taurine is the most predominant amino acid in poultry bile, constituting 62% of its composition.
• Role of Cholecystokinin (CCK): Arrival of lipid droplets triggers the release of cholecystokinin (CCK), stimulating pancreatic and bile secretions.
• Composition of Bile: Bile contains sodium salts, phospholipids, cholesterol, and taurine (predominant at 62% in poultry). Taurine is the most predominant amino acid at 62% in poultry bile.

• Action of Bile Salts: Bile salts reduce tension at the oil-water interface, stabilizing lipid particles in the aqueous environment. Approximately 97% of bile salts passively diffuse through the small intestine and are recycled enterohepatically in the liver.
• Role of Pancreatic Lipase (PTL): Pancreatic lipase cleaves lipids into free fatty acids and monoacylglycerol at an optimal alkaline pH. This cleavage occurs below 0.1 mm at the sn1‐ and sn3‐ positions, releasing two free fatty acids and sn‐2‐ monoacylglycerol.
• Involvement of Co-lipase: Co-lipase improves lipid cleavage and restores pancreatic lipase function inhibited by bile salts.
• Location of Fat Digestion: Most fat digestion occurs in the jejunum (around 75%), with a preparative role in the duodenum (around 15%-25%) due to the faster passage time in broiler chickens.
• Absorption in Jejunum: The majority of fat absorption occurs in the jejunum

Absorption of Lipids in Poultry:

“ In poultry, unlike mammals, fatty acids are absorbed directly by enterocytes without the formation of chylomicrons”

• Transport via Portomicrons: Lipids are transported in a mammalian chylomicron-like form called portomicrons in poultry blood. Portomicrons are lined with protruding apolipoproteins and are too large to be metabolized by the liver.
• Metabolism of Portomicrons: Portomicrons are cleaved by lipoprotein lipase, producing free fatty acids and monoacylglycerols. Free fatty acids are transported to muscle tissues or reesterified and stored as triglycerides in adipose tissue.
• Factors Influencing Lipid Digestion and Absorption: Lipid digestion and absorption are influenced by bird and diet-related factors, including the supply of bile salts, pancreatic lipase, and co-lipase.

Digestive Limitation of Lipids in Young Chicks:

• Adaptive Response to Feed Transition: Young chicks undergo rapid growth during the first-week post-hatch, necessitating adaptations in the gastrointestinal tract to efficiently acquire, digest, and utilize nutrients.
• Increased Intestinal Mass and Enzyme Activity: The intestinal mass for the proventriculus, gizzard, and small intestine increases rapidly relative to body weight, accompanied by an increase in total digestive enzyme activity, including lipase, amylase, trypsin, and chymotrypsin.
• Inadequate Lipase Production: Despite the increase in lipase activity, reported increases may be insufficient to match total feed intake, and the maximal increase in pancreatic lipase secretion occurs later compared to other digestive enzymes.
• Age-Related Physiological Limitation in Lipid Utilization: Limited production of fatty acid-binding proteins (FABPs) and bile salts, essential for lipid utilization, contributes to an age-related limitation in the effective utilization of lipids, particularly saturated animal fats.
• Effects of Delayed Feed Access and Pos thatch Stress: Delayed access to feed post-hatch, common in practical settings, and stress from posthatch handling and transport exacerbate the limited fat utilization capability of young chicks.

Application of Exogenous Emulsifiers:

• Definition and Properties: Exogenous emulsifiers are molecular surfactants with hydrophobic and hydrophilic properties, which inhibit coalescing of hydrolyzed lipid droplets and reduce surface tension at the oil-water interface, facilitating emulsion formation and stabilization.
• Widely Used in Food and Animal Production Industries: Emulsifiers are utilized in various food products and industries, including mayonnaise, margarine, animal feeds, and supplements.
• Natural and Synthetic Emulsifiers: Emulsifiers can be natural (e.g., bile, phospholipids) or synthetic (e.g., lysolecithin, glycerol monostearate), with efficacy dependent on their hydrophilic-lipophilic balance (HLB).
• Improvement in Fat Digestibility and Energy Efficiency: Exogenous emulsifier supplementation improves fat digestibility, and energy efficiency, and may confer gut health-promoting, neuroprotective, and antioxidative properties.
• Growth Performance Enhancement: Emulsifier supplementation in broiler diets leads to improved body weight gain, daily weight gains, and feed efficiency, attributed to enhanced nutrient digestibility and higher energy efficiency.
• Varied Effects and Considerations: Discrepancies in growth performance may arise due to differences in emulsifier efficacy, supplemental lipase use, and lipid levels and sources in basal diets. the overall improvements in nutrient digestibility may be attributed to the alteration of the phospholipid bilayer of cell membranes, potentially enhancing nutrient uptake

Blood Metabolites Effects of Dietary Emulsifiers:

• Lowered Plasma Cholesterol and Triglyceride Concentrations: Previous studies have consistently reported reductions in plasma cholesterol and triglyceride concentrations with dietary emulsifiers (Huang et al., 2007; Roy et al., 2010; Zhao & Kim, 2017). This reduction is attributed to a rapid elimination rate of chylomicrons from the blood, potentially due to improved hydrolysing action of lipoprotein lipase (Roy et al., 2010).
• Possible Mechanisms for Reduction: Emulsifiers may enhance lipoprotein lipase activity, leading to the release of free fatty acids and monoacylglycerols from triglycerides sequestered in chylomicrons. Additionally, emulsifiers may stabilize the phospholipid coating of chylomicrons, reducing the secretion rate of cholesterol and triacylglycerols into the blood (Jones et al., 1992).
• Inconsistencies and Further Studies: While reductions in cholesterol and triglyceride levels are commonly reported, some inconsistencies, including elevated total cholesterol levels, have been observed in previous publications (Bontempo et al., 2018; Saleh et al., 2020). Further studies are needed to elucidate the mechanisms behind the effects of emulsifiers on blood metabolites.
• Increased Levels of Other Blood Plasma Metabolites: Emulsifier supplementation has been associated with increased levels of globulins and lipase in blood plasma (Oketch et al., 2022; Saleh et al., 2020). Higher lipase activity may be associated with improved lipid digestibility, while increased globulin levels could indicate enhanced immune function (Guerreiro Neto et al., 2011; Ho Cho et al., 2012; Saleh et al., 2020).
• These points summarize the effects of dietary emulsifiers on blood metabolites, including cholesterol, triglycerides, globulins, and lipase, and suggest possible mechanisms underlying these effects, with references provided for further reading

Ileal Histomorphology and Gut Health Effects of Dietary Emulsifiers:

• Epithelial Changes: Emulsifiers have been shown to trigger epithelial changes in the gut that improve nutrient digestibility and overall gut health (Boontiam et al., 2017; Brautigan et al., 2017). These changes include longer villus heights (VH), deeper crypt depth (CD), and higher VH: CD ratios, indicating enhanced intestinal absorption activity (Wickramasuriya, Macelline, et al., 2020).
• Improvements in Villus Morphology: Marginal improvements in villus absorptive surface area have also been reported with emulsifier supplementation (Oketch et al., 2022). These morphological enhancements may result from synergistic interactions among feed ingredients, including dietary emulsifiers (Brautigan et al., 2017).
• Gene Expression Regulation: The addition of lysolecithin has been associated with the upregulation of genes such as carbonic anhydrase VII and interleukin 8-like 2, which are linked to better gut health (Cloft et al., 2021). However, some studies have reported no significant effects of emulsifiers on gut morphology (Tenório et al., 2022; Wickramasuriya, Cho, et al., 2020).
• Impact on Intestinal Microbiota: Emulsifiers may influence the composition of the intestinal microbiota, which is crucial for gut health. Glycerol PEGR has been shown to reduce caecal Clostridium populations in synergy with xylanase in tallow-incorporated diets (Kubiś et al., 2020). Soy lecithin supplementation has been associated with lower Firmicutes and higher Bacteroidetes levels, potentially impacting leanness and reducing abdominal fat deposition (Shen et al., 2021; Haetinger et al., 2021; Lai et al., 2018).

Visceral Organ Weights and Carcass Traits:

• Liver and Pancreas Weights: Dietary emulsifier supplementation has been associated with improved liver and pancreas weights, indicating increased function in terms of lipid biosynthesis and metabolism (Boontiam et al., 2017; Oketch et al., 2022; Wickramasuriya, Macelline, et al., 2020). The liver plays a vital role in cholesterol conversion to bile salts and lipid biosynthesis, while the pancreas is involved in lipid metabolism and secretion of digestive enzymes.
• Impact on Immunological Organs: Emulsifier supplementation may affect immunological organs such as the bursa of Fabricius and the spleen. Increased bursa of Fabricius weights suggests potential enhancement of humoral immune function, while reductions in spleen weight could indicate immunosuppressive effects (Ho Cho et al., 2012; Allahyari-Bake and Jahanian, 2017; Upadhaya et al., 2018).
• Carcass Traits: Dietary emulsifiers have been reported to improve breast and carcass percentages, potentially enhancing carcass quality by reducing abdominal fat percentages (Boontiam et al., 2017; Ge et al., 2019). The use of lower-energy diets with emulsifiers has shown promise in lowering abdominal fat percentages, likely due to reduced lipogenesis activity (Ge et al., 2019).
• Meat Quality: Emulsifier supplementation has been associated with improved meat quality, including increased muscle yellowness and tenderness, as well as reduced lipid peroxidation and oxidative stress (Oketch et al., 2022; An et al., 2020; Saleh et al., 2020). These improvements may be attributed to emulsifiers' involvement in lipid metabolism and antioxidative properties.

HLB value/scale:

• HLB (Hydrophilic-Lipophilic Balance):
• HLB is a measure of the balance between the hydrophilic (water-loving) and lipophilic (oil-loving) parts of an emulsifier molecule, which governs its functionality at interfaces.
• It is used as a guide for selecting emulsifiers suitable for specific applications in food formulations.
• Calculation of HLB:
• The initial proposed method for calculating HLB was HLB = L/T × 20, where L is the molecular weight of the hydrophilic part and T is the total molecular weight.
• Alternatively, HLB can be calculated by summing the contributions of various functional groups using the equation: HLB = Σ (hydrophilic values) - Σ (lipophilic values) + 7.
• Hydrophilic and lipophilic group values are listed in Table 3-2, and the sum determines the HLB value of the emulsifier.
• Guidelines for HLB Values:
• HLB values guide the functionality of emulsifier systems:
• HLB of 3–6 is suitable for water-in-oil emulsifiers.
• HLB of 7–9 is suitable as a wetting agent.
• HLB of 10–18 is suitable for oil-in-water emulsifiers.
• Experimental Determination of HLB:
• Experimentally, the optimum HLB for a particular system is determined by preparing emulsifier blends at intervals of 0.5 HLB units.
• The blends are prepared using a combination of emulsifiers, and stability is assessed through emulsion formation and thickness measurement.
• The best chemical types of emulsifiers are chosen based on stability trials and compatibility with the system's pH and other ingredients.
• Fine-tuning involves running trials at smaller HLB intervals and various concentrations to find the minimum amount required for desired emulsion stability.
• Considerations:
• HLB values are empirical and somewhat imprecise, so adjustments may be needed based on practical trials.
• Emulsifiers interact with other ingredients, necessitating reassessment of optimum HLB when formula changes are made, especially involving proteins or gums.
• Protein Structure and Behavior:
• Proteins consist of amino acid chains with hydrophobic and hydrophilic regions.
• Under appropriate conditions, proteins can unfold, allowing their hydrophobic regions to interact with oil while hydrophilic regions remain in the water.
• Protein as Emulsifying Agents:
• Proteins act as amphiphiles at interfaces, lowering surface tension and facilitating emulsification.
• Both soluble (e.g., myosin) and insoluble proteins (e.g., egg yolk lipoproteins) can emulsify oil in food systems.
• Interaction with Emulsifiers:
• Proteins can interact with emulsifier molecules through complexation and competition.
• Emulsifiers can bind to proteins, altering their conformation and affecting their emulsifying properties.
• Effect on Interfacial Properties:
• Competitive adsorption occurs when both proteins and emulsifiers compete for interfacial area.
• Displacement may happen when a more surface-active compound displaces a less active material from the interface.
• Interaction at the interface can lead to more efficient packing, decreasing interfacial tension further.

When proteins interact with emulsifiers, several phenomena occur:

Carbohydrate and emulsifier:

• Emulsifiers such as diacetyl tartrate ester of monoglyceride (DATEM), glycerol monostearate (GMS), and sodium stearoyl lactylate (SSL) modify starch gelatinization.
• They raise the swelling temperature of starch granules, influencing the onset of gelatinization.
• Emulsifiers like GMS significantly increase paste viscosity after gelatinization, impacting the texture and consistency of the final product.
• SSL inhibits swelling to a lesser extent but increases paste viscosity comparably to GMS.
• Emulsifiers interact with starch granules, forming starch-emulsion complexes that stabilize the granules, retard water penetration, and slow swelling during heating.
• These interactions primarily involve amylose, leading to the formation of amylose-emulsion complexes, which play a role in controlling starch solubility and texture.
• Temperature plays a crucial role in starch gelatinization, and emulsifiers influence this process by altering temperature-dependent properties.
• Higher temperatures accelerate starch gelatinization, leading to increased swelling of starch granules and solubilization of amylose and amylopectin molecules.
• Emulsifiers can elevate the gelatinization temperature of starch, requiring more energy input to initiate the process.
• This elevated temperature threshold helps ensure proper gelatinization occurs during baking or cooking, leading to improved texture, structure, and moisture retention in the final product.
• At elevated temperatures, emulsifiers facilitate the formation of stable complexes between starch and emulsion droplets, enhancing the stability of starch-based systems and reducing retrogradation (re-crystallization) upon cooling.
• However, excessively high temperatures can lead to over-gelatinization or degradation of starch, resulting in undesirable changes in product texture and quality.

• Blend the mixture of oil, water, and emulsifier in an emulsion until homogenous.
• Collect a sample of the colloidal mixture.
• Use the WHO/M/13.R4 protocol (1999) for visual assessment of emulsion stability.

• Calculate electricity consumption (kW/(T/h)) using the formula: Electricity consumption, Electricity consumption, kW/(T/h) = (Amp × Vol × √3 × power factor)/(T/h ×1000) Where T/h = pelleting production rate tonne p/hour Amp = average pellet mill motor ampere Vol = feed mill voltage Power factor 0.93)

• Measure temperatures of hot mash and hot pellet feed samples using a digital thermometer.
• Calculate the temperature difference between hot mash and hot pellet feed samples

• Follow the AOAC (2005) method for moisture content determination.
• Calculate moisture content using the formula: Moisture Content (%)=Initial weight−Dry weightInitial weight×100Moisture Content (%)=Initial weightInitial weight−Dry weight×100

• Measure water activity directly using an Aqua Lab Water Activity Meter (Decagon, Series 3TE).

• Follow the Luff-Schoorl method (ISI, 2002) for starch gelatinization determination.

• Determine the acid value and peroxide value using AOCS (1999) methods.
• Conduct tests at intervals over 14 days.

• Perform mould count analysis based on AOAC (2005) standards.

• Determine bulk density using ASAE (1998) standards.
• Calculate pellet durability index using ASAE S269.4 (1998) guidelines.
• Screen feed samples through wire sieves with specific opening sizes to quantify powdery feed percentage.

Which is Best?

Key Points: Impact of High Calcium Conditions on Fatty Acid Absorption

• Calcium and Fatty Acid Absorption: High dietary calcium can negatively impact fatty acid absorption.
• Insoluble Complexes Formation: Excess calcium forms insoluble complexes with magnesium and phosphate, reducing the availability of bile acids.
• Bile Acids: Essential for emulsifying fats; when bound by calcium complexes, their effectiveness is diminished.
• Reduced Fat Digestion: Impaired interaction between bile acids and fats leads to decreased fatty acid absorption.
• Increased Bile Acid Excretion: Binding of bile acids to complexes results in higher excretion in feces and limits reabsorption.
• Bile Salts vs. Emulsifiers:
• Bile Salts: Natural surfactants that emulsify fats but may be hindered by high calcium.
• Emulsifiers: Can be added to diets to improve fat digestion and absorption in high-calcium situations.
• Mitigation Strategy: Using emulsifiers can enhance fat digestion and absorption, compensating for the negative effects of excess calcium.

Conclusion