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Introduction
E492, also known as sorbitan tristearate (STS), is a non-ionic emulsifier produced by the complete esterification of sorbitan (dehydrated sorbitol) with three molecules of stearic acid. Unlike E491 (sorbitan monostearate, which has three free hydroxyl groups), E492 has all three hydroxyl groups esterified, leaving no free hydroxyls. The molecule is therefore extremely lipophilic with an HLB value of approximately 2.1-3.0. E492 is primarily used as a co-emulsifier and crystallization modifier in margarine, confectionery fats, and chocolate. It is also used as a defoaming agent (anti-foaming) and as a texturizer in some bakery products. E492 is approved in EU, USA (21 CFR 172.842), Japan, and Codex. It is often used in combination with more hydrophilic emulsifiers (like polysorbates) to fine-tune emulsion properties.
CAS Number
26658-19-5 (sorbitan tristearate). Also 9007-43-6 (sorbitan stearate mixture, which includes mono, di, and tri).
Synonyms
Sorbitan tristearate, STS, Sorbitan trioctadecanoate, E492, Span 65 (trade name).
Topic Headings
1. Chemical structure and role as a crystallization modifier (detailed paragraph form)
Sorbitan tristearate has three stearic acid chains esterified to the sorbitan ring, with no remaining free hydroxyl groups. This complete esterification makes the molecule non-polar and extremely lipophilic. The three long saturated chains (each C18:0) can pack tightly together in the solid state, forming crystals with high melting points (55-65°C). In food systems, E492 does not function primarily as an emulsion stabilizer (despite being an emulsifier) but rather as a crystal habit modifier. When added to fats and oils, E492 adsorbs onto the surface of growing fat crystals (e.g., cocoa butter, palm oil, milk fat) and modifies their growth pattern. It can promote the formation of desirable crystal polymorphs (e.g., beta-prime in margarine) and inhibit the formation of undesirable ones (e.g., beta crystals that cause graininess). This is particularly important in margarine, where E492 prevents the formation of large, gritty crystals that give a sandy texture. In chocolate, E492 (often in combination with E476) helps stabilize the beta V polymorph of cocoa butter, preventing fat bloom. At usage levels of 0.2-0.5% in fat systems, E492 reduces crystal size by 50-70% and produces a smoother, more uniform texture. Because it has no hydrophilic groups, E492 does not stabilize water-in-oil emulsions on its own but works as a co-emulsifier by strengthening the interfacial film formed by other emulsifiers.
2. Physical and chemical properties (list form)
• Appearance — White to cream-colored waxy beads, flakes, or powder.
• Odor — Very faint, characteristic fatty odor.
• Melting range — 55-65°C (higher than E491 due to complete esterification and three stearic chains).
• Solubility — Soluble in fats and oils (>60°C); insoluble in water; soluble in hot ethanol and hot isopropanol; insoluble in cold ethanol and propylene glycol.
• HLB value — 2.1-3.0 (very lipophilic; only suitable for water-in-oil emulsions).
• Acid value — Maximum 15 mg KOH/g (slightly higher than E491 due to potential free stearic acid).
• Saponification value — 175-190 mg KOH/g (higher than E491 because of three ester bonds per molecule).
• Hydroxyl value — 15-40 mg KOH/g (very low, indicating minimal free hydroxyl groups; ideally near zero for pure tristearate).
• Iodine value — Typically <5 (from stearic acid, which is fully saturated).
• Water content — Maximum 2% (Karl Fischer titration).
• Sorbitan content — 20-25% (by weight; lower than E491 because of three stearic acids).
• Stearic acid content — 75-80%.
• Triester content — Typically 60-80% (rest is monoester and diester).
• Bulk density — 0.5-0.7 g/cm³.
• Contact angle with water — Very high (>90°), indicating strong lipophilicity (water does not wet the powder).
3. Manufacturing process (paragraph form)
E492 is produced similarly to E491 but with an excess of stearic acid to drive the reaction toward triester formation. First, sorbitol is dehydrated to sorbitan at 200-250°C under vacuum. Second, the sorbitan is reacted with a large excess of stearic acid (typically 3.5-5.0 moles of stearic acid per mole of sorbitan) at 200-250°C under vacuum for 6-10 hours, with an alkaline catalyst (sodium hydroxide or potassium carbonate). The long reaction time and high temperature favor complete esterification, converting most of the free hydroxyl groups to esters. After the reaction, excess stearic acid is removed by steam distillation or wiped-film evaporation under vacuum (or left in the product as a processing aid, which is acceptable up to certain limits). The product is then neutralized, cooled, and formed into beads or flakes. Quality control parameters include free stearic acid (<5-10%, which acts as a processing aid but is not considered harmful), monoester/diester/triester ratio (by HPLC), acid value, and hydroxyl value (low hydroxyl value confirms high triester content). Unlike E491, some free stearic acid is allowed in E492 because it does not negatively affect functionality; in fact, it can improve dispersion in fat systems.
4. Applications and typical usage levels (list form)
• Margarine and low-fat spreads — 0.2-0.5% modifies fat crystallization; prevents formation of large, gritty beta crystals; produces smooth, spreadable texture; works synergistically with lecithin or E471.
• Chocolate and chocolate coatings — 0.1-0.3% (often with E476) stabilizes beta V polymorph; reduces fat bloom (white discoloration) by 50-70%; improves gloss and snap.
• Confectionery fats (compound coatings, filling fats) — 0.2-0.5% controls crystallization of palm oil, shea butter, and lauric fats; prevents graininess and oil separation.
• Ice cream — 0.1-0.2% improves overrun and reduces ice crystal growth; often used with E433 (polysorbate 80) for synergistic stabilization.
• Shortenings for baking — 0.2-0.4% improves creaming properties; gives finer fat crystal structure; results in more uniform baked goods.
• Defoaming agent in fermentation and food processing — 0.01-0.05% controls foam in yeast production, beer brewing, and juice processing; more effective than E491 because it has no hydrophilic groups.
• Pan release agents (non-stick sprays for baking) — 0.3-0.7% in oil-based sprays; provides excellent release properties; reduces smoke point depression.
• Salad dressings (water-in-oil types) — 0.1-0.3% stabilizes water droplets in continuous oil phase; prevents phase separation.
• Pharmaceutical and cosmetic applications (non-food) — Used as a tablet lubricant, emulsion stabilizer, and thickening agent.
5. Stability, compatibility, and storage (paragraph form)
E492 is extremely stable due to its fully saturated nature. It has a shelf life of 24 months or more when stored in sealed, dry containers below 30°C, away from light and moisture. Unlike unsaturated emulsifiers, it does not oxidize or become rancid (iodine value <5). E492 is heat-stable up to 200°C; above 220°C, it begins to decompose and release free fatty acids, causing darkening and off-odors. It is stable at pH 3-9; at pH <3, slow hydrolysis occurs (but much slower than for monoesters because triesters have no free hydroxyl groups to initiate hydrolysis). At pH >9, saponification occurs rapidly, especially at high temperatures. E492 is compatible with all common food ingredients, including other emulsifiers, fats, oils, proteins, and carbohydrates. It is particularly compatible with E491 (sorbitan monostearate) and E433 (polysorbate 80); these three are often used together as a "emulsifier system" because E491 and E492 have different HLB values and complement each other. E492 is not compatible with strong oxidizing agents. For best dispersion, E492 should be melted with the fat phase at 65-75°C before incorporation. Do not add directly to cold water or cold oil — it will not dissolve. In dry powder form, E492 may be dusty; use appropriate dust control measures during handling.
6. Regulatory status, safety, and toxicology (paragraph form)
JECFA has established an ADI of 0-25 mg/kg body weight for sorbitan tristearate (as a group with sorbitan monostearate and sorbitan trioleate). The same ADI as E491 applies. Toxicological studies show that E492 is even less absorbed than E491 because it has no free hydroxyl groups and cannot form hydrogen bonds with water. Over 95% of ingested E492 passes through the gastrointestinal tract unchanged and is excreted in feces. The small amount that is hydrolyzed (by pancreatic lipase) produces sorbitan and stearic acid, both of which are low-toxicity compounds. No genotoxicity, carcinogenicity, or reproductive toxicity has been observed in animal studies. A 2-year rat feeding study at 5% of the diet (approximately 2500 mg/kg/day) showed no adverse effects. EU maximum levels: 10 g/kg in margarine and spreads, 5 g/kg in chocolate, 5 g/kg in fine bakery wares, 5 g/kg in ice cream. USA: GRAS under 21 CFR 172.842 with no specific limits when used as an emulsifier, stabilizer, or defoaming agent. E492 is permitted in organic foods in some jurisdictions (non-organic allowed under restricted conditions). Allergic reactions are extremely rare. E492 is dairy-free, gluten-free, and vegan (when sourced from vegetable stearic acid, which is typical). Unlike E491, E492 does not contain sorbitol residues that could trigger sorbitol sensitivity; it is completely safe for individuals with sorbitol intolerance.
7. Analytical methods for identification and quantification (list form)
• Thin layer chromatography (TLC) — Silica gel plate with chloroform:methanol:water (80:20:2) as mobile phase; E492 has much lower Rf (more lipophilic) than E491; visualization with sulfuric acid spray and charring.
• High performance liquid chromatography (HPLC) — Reverse-phase C18 column with acetonitrile:tetrahydrofuran gradient and evaporative light scattering detection (ELSD); separates monoester, diester, and triester; E492 shows dominant triester peak (>60%).
• Gas chromatography (GC) — After hydrolysis and derivatization (methylation for stearic acid; silylation for sorbitan), quantifies sorbitan:stearic acid ratio; E492 has 1:3 ratio (sorbitan to stearic acid) compared to E491's 1:1 ratio.
• Infrared spectroscopy (FTIR) — Characteristic peaks: carbonyl ester at 1735 cm⁻¹ (strong); no significant O-H peak at 3400-3500 cm⁻¹ (indicating complete esterification); C-H at 2850-2950 cm⁻¹.
• Hydroxyl value titration — Very low (15-40 mg KOH/g) compared to E491 (235-260); confirms triester-rich composition.
• Acid value titration — Measures free stearic acid (typically 5-15 mg KOH/g).
• Saponification value titration — Higher than E491 (175-190 vs 145-160) because of three ester bonds.
• Water content (Karl Fischer titration) — Maximum 2%.
• Melting point determination — Capillary method; typical range 55-65°C (higher and sharper than E491).
• HLB calculation — From saponification and hydroxyl values: HLB = 20 × (1 - S/HV). For E492, HV is very small, so HLB approaches 0 (calculated HLB 2-3).
• Hydrophilic-lipophilic balance (experimental) — Emulsion inversion temperature method; confirms HLB <3.
