What is E305?
Complete guide to understanding E305 (Ascorbyl Stearate) in your food
The Quick Answer
E305 is a fat-soluble form of vitamin C created by chemically binding ascorbic acid (vitamin C) to stearic acid (an 18-carbon saturated fatty acid)—functioning as an antioxidant and preservative that prevents fats and oils from becoming rancid.
It’s used in margarine, oils, baked goods, and other fatty foods where water-soluble vitamin C would be less effective.
E305 is considered safe by regulatory authorities. Like E304 (ascorbyl palmitate), E305 is assumed to completely break down into vitamin C and stearic acid during digestion. Limited toxicological data exists, but available evidence supports safety at approved food-use levels.
📌 Quick Facts
- Category: Synthetic fat-soluble antioxidant (vitamin C ester)
- Chemical Name: Ascorbyl stearate (6-O-stearyl-L-ascorbic acid)
- Chemical Formula: C₂₄H₄₀O₇
- Source: Chemically created by esterifying ascorbic acid with stearic acid (18-carbon saturated fatty acid)
- Function: Fat-soluble antioxidant; prevents rancidity in oils/fats; more effective than water-soluble E300 in fatty products
- Found in: Margarine, oils, baked goods, dairy products, nuts, prepared meals
- Safety Status: FDA GRAS; EFSA approved; approved in EU, USA, Canada, Australia, New Zealand
- Key Feature: Fat-soluble unlike water-soluble E300; similar to E304 but with longer-chain fatty acid (stearic vs palmitic)
What Exactly Is It?
E305 is ascorbyl stearate—a fat-soluble vitamin C ester produced by chemically binding ascorbic acid (vitamin C) with stearic acid (18-carbon saturated fatty acid).
Its chemical formula is C₂₄H₄₀O₇; molecular weight 442.58.
Production: Food-grade E305 is manufactured by esterifying ascorbic acid with stearic acid using chemical synthesis (acylation). The result is a fat-soluble powder that appears as white to off-white crystalline material.
Key distinction from E304: E305 uses stearic acid (18-carbon saturated fatty acid) as the ester group, whereas E304 uses palmitic acid (16-carbon saturated fatty acid). This longer carbon chain makes E305 even more lipophilic (fat-soluble) than E304.
Mechanism: E305 functions identically to E300 (ascorbic acid) as an antioxidant—donating electrons to neutralize free radicals before they can damage fats and cause rancidity. Because E305 is fat-soluble, it disperses throughout fatty/oily products more effectively than water-soluble E300.
Key functional assumption: Regulatory authorities assume that E305 completely hydrolyzes (breaks down) in the gastrointestinal tract into ascorbic acid (vitamin C) and stearic acid (a common dietary saturated fatty acid) during digestion.
Where You’ll Find It
E305 appears in fatty and oily food products, particularly margarine:
• Margarine (primary use)
• Vegetable oils
• Baked goods with added oils/fats
• Butter replacements
• Nuts and nut products
• Prepared meals with high fat content
• Dairy products with fat content
• Meat products with added fat
• Snack foods
• Cosmetics and skincare products
E305 is less common than E304 in most food applications, but appears with higher frequency in margarine specifically due to historical regulatory preference in that category.
Why Do Food Companies Use It?
E305 serves critical functions in fatty foods, particularly margarine:
Superior effectiveness in fats: Because E305 is fat-soluble, it disperses throughout margarine and fatty products effectively, whereas water-soluble E300 would separate from the fat phase.
Prevents oxidation of saturated fats: Protects margarine and other fat-based products from oxidation and rancidity development.
Longer-chain advantage (vs E304): The 18-carbon stearic acid gives E305 greater lipophilicity than E304’s 16-carbon palmitic acid, potentially improving distribution in very fatty products.
Dual benefit—preservation and vitamin fortification: E305 serves as both preservative and vitamin C source (after hydrolysis to ascorbic acid).
History of use in margarine: Established track record in margarine production with no documented safety issues over decades of use.
Regulatory approval: Globally approved with acceptance from major food safety authorities.
Is It Safe?
Yes—E305 is considered safe by regulatory authorities. Toxicological data is limited (similar to E304), but available evidence supports safety at approved food-use levels based on assumed complete hydrolysis to vitamin C and stearic acid.
The FDA classifies ascorbyl stearate as GRAS (Generally Recognized as Safe).
The EFSA has approved E305 for use in margarine and similar fat-based products.
✓ GREEN SAFETY RATING – NO DOCUMENTED CONCERNS: E305 has:
• No documented genotoxicity (DNA damage)
• No documented carcinogenicity
• No documented reproductive or developmental toxicity
• No documented organ toxicity at food-use levels
• Assumed complete hydrolysis to safe components (vitamin C + stearic acid)
• Stearic acid component: common dietary saturated fat with long history of safe food use
• Ascorbic acid component: no safety concerns at food levels
• Limited but available toxicological data support safety (similar profile to E304)
Safety is based on: (1) chemical similarity to approved E304, (2) assumed complete harmless hydrolysis to vitamin C and stearic acid, (3) extensive history of safe use of stearic acid in food fats, and (4) safety of ascorbic acid at food levels.
What Are The Health Concerns?
E305 has no documented health concerns at food-use levels. However, some considerations exist:
Limited specific toxicological data for E305 itself: Unlike some additives with extensive testing, specific toxicological studies on E305 are limited. However, this reflects data gaps rather than identified safety problems. Safety is inferred from chemical similarity to E304 and from the safety of component compounds (vitamin C and stearic acid).
Complete hydrolysis assumption: Regulatory authorities assume E305 completely breaks down into vitamin C and stearic acid during digestion. While this is chemically reasonable and supported by available data, comprehensive human absorption studies specifically for E305 are limited.
Stearic acid content (minimal concern): E305 contributes stearic acid to diet (~59% of E305 mass by weight). However, stearic acid is a ubiquitous dietary saturated fatty acid present in far larger amounts from butter, meats, coconut oil, and other natural foods. The additive represents only a tiny fraction of typical daily stearic acid intake.
Saturated fat considerations (general, not E305-specific): High saturated fat intake is associated with increased cardiovascular disease risk. However, E305 contributes minimal saturated fat compared to the fatty products it’s used in (margarine, oils).
No documented adverse effects: Decades of use in margarine in Europe and other regions with no documented adverse events in post-market surveillance.
Comparison: E304 vs E305
E304 and E305 are functionally very similar:
• E304 (Ascorbyl Palmitate): Vitamin C + palmitic acid (16-carbon fatty acid); C₂₂H₃₈O₇; MW 414.55
• E305 (Ascorbyl Stearate): Vitamin C + stearic acid (18-carbon fatty acid); C₂₄H₄₀O₇; MW 442.58
The difference is chain length: E305’s stearic acid is 2 carbons longer than E304’s palmitic acid. This makes E305 slightly more lipophilic (fat-soluble), potentially providing marginal advantage in very fatty products. In practice, both serve identical antioxidant functions.
Natural vs Synthetic Version
E305 is entirely synthetic—it does not occur naturally in foods.
It is created through chemical esterification of ascorbic acid (vitamin C) with stearic acid (a saturated fatty acid). While stearic acid is found naturally in foods (butter, meat, coconut oil), the ester is a synthetic combination.
However, E305 is designed to be completely hydrolyzed back into natural components (vitamin C and stearic acid) during digestion, making it functionally equivalent to consuming vitamin C and dietary fat separately.
Natural Alternatives
Want to avoid E305?
Natural antioxidant alternatives include:
• Vitamin E/Tocopherols (E306) – natural fat-soluble antioxidant
• Rosemary extract – natural fat-soluble antioxidant
• Ascorbic acid (E300) – water-soluble vitamin C (less effective in fats)
• Accept shorter shelf-life – use margarine/oils without preservation; consume quickly
The Bottom Line
E305 (Ascorbyl Stearate) is a fat-soluble form of vitamin C used primarily in margarine and other fatty foods to prevent oxidation and rancidity. It is considered safe by regulatory authorities, with safety based on assumed complete hydrolysis to vitamin C and stearic acid—both safe dietary components.
Regulatory Approval: FDA GRAS, EFSA approved, global acceptance. Decades of use in margarine with no documented safety issues.
Key Safety Assumption: E305 completely breaks down into vitamin C and stearic acid during digestion, both of which are safe dietary components. This assumption is supported by chemical stability data and has not been contradicted.
Limited but Safe Toxicological Data: Specific toxicological studies on E305 are limited, explaining conservative regulatory approach. However, available data combined with chemical similarity to approved E304 support safety at food-use levels.
Fat-Solubility Advantage: The primary functional advantage of E305 over water-soluble E300 is fat-solubility, enabling effective antioxidant protection in fats, oils, and fatty foods where water-soluble forms cannot disperse effectively.
Stearic Acid Component Safe: Stearic acid is a common dietary saturated fatty acid present in butter, meat, coconut oil, and other natural foods in far larger amounts than E305 contributes.
Primary Application—Margarine: E305 is used primarily in margarine, where its stability and fat-solubility provide preservation benefits. Margarine without E305 or similar antioxidants would develop rancid flavors within weeks of production.
Recommendation: E305 is safe for food use at approved levels. It is functionally valuable in margarine and similar fat-based products. Like other E300-E304 compounds, E305 is a form of vitamin C and is beneficial rather than concerning. For individuals preferring to avoid all synthetic additives, natural alternatives (vitamin E extract, rosemary extract) exist but may provide less effective preservation.