What is E101?
Complete guide to understanding E101 (Riboflavin/Vitamin B2) in your food
The Quick Answer
E101 is riboflavin (also called vitamin B2 or flavin), a water-soluble B-complex vitamin essential for energy production and cellular function—used as a food colorant (providing yellow color) and nutritional fortification agent to supplement foods with essential vitamin B2.
It’s a naturally occurring coenzyme precursor that functions as a yellow food colorant while providing essential nutrition, used in breakfast cereals, bread, fortified dairy products, and numerous processed foods to both color and enrich products with vital vitamin B2.
E101 riboflavin is a natural food additive with dual function (coloring + nutrition), regulatory approval across multiple jurisdictions, and exceptional safety profile—both as food additive and as essential nutrient required for human health, with no documented adverse effects at food-use or supplementation levels.
📌 Quick Facts
- Category: Natural Vitamin, Food Colorant (Yellow), Essential Nutrient, Coenzyme Precursor
- Source: Naturally occurring vitamin; produced commercially from yeasts (fermentation), genetically modified bacteria, or chemical synthesis
- Found in: Breakfast cereals, bread, fortified milk, dairy products, instant soup, cheese, processed foods, fish fingers, margarine, sauces
- Safety: EFSA approved; FDA approved; JECFA approved; no ADI set (considered safe at any level); essential nutrient status
- Natural or Synthetic: Naturally occurring vitamin; produced both through fermentation (natural source) and chemical synthesis
- Vegan/Vegetarian: Yes (when fermented from non-milk sources; commercially not derived from milk despite capability)
- Key Advantage: Essential nutrient with dual function (coloring + nutrition); exceptional safety profile; naturally occurring in many foods; no toxicity known; photosensitizing property useful in some applications
- Key Characteristic: Poorly water-soluble (limiting coloring applications); yellow color; bitter taste; photosensitizer; water-soluble vitamin not stored in body
- Chemical Formula: C₁₇H₂₀N₄O₆ (riboflavin); E101(ii) is phosphorylated form C₁₇H₂₀N₄NaO₉P
The Critical Context—Essential Nutrient With Dual Food Additive Function
E101 riboflavin is vitamin B2—an essential nutrient required for human health that functions both as food colorant (yellow coloring) and nutritional fortification agent, with dual E-number designations (E101(i) for riboflavin, E101(ii) for riboflavin-5′-phosphate sodium phosphorylated form), approved for food use with exceptional safety profile reflecting its status as essential vitamin with no documented toxicity at food-use, supplementation, or therapeutic dose levels.
What Exactly Is It?
E101 is riboflavin (vitamin B2, 7,8-dimethyl-10-ribitylisoalloxazine), a water-soluble B-complex vitamin with molecular formula C₁₇H₂₀N₄O₆ and molecular weight of 376.36 g/mol.
Riboflavin is discovered by Richard Kuhn in 1933 and was originally identified as a component of egg white, liver, and yeast. It is a naturally occurring organic compound essential for human metabolism and energy production. The vitamin is found naturally in both plant and animal sources including dairy products, eggs, liver, meat, poultry, fish, green vegetables (broccoli, spinach), nuts, enriched grains, and mushrooms.
Physically, E101 appears as needle-shaped yellow crystals with bitter taste. The compound is practically insoluble in water (84.7 mg/L solubility at 20°C), poorly soluble in alcohol, but soluble in acidic solutions. This limited water solubility restricts its applications as food colorant compared to water-soluble alternatives.
Chemically, E101 functions through two distinct mechanisms: (1) as a coenzyme precursor—riboflavin is converted in the body to two major coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which participate in hundreds of enzymatic reactions involved in energy metabolism, antioxidant defense, and detoxification; and (2) as a yellow food colorant providing the characteristic yellow hue to foods and beverages.
Where You’ll Find It
E101 riboflavin appears in numerous foods as both colorant and nutritional fortification:
• Breakfast cereals and cereal products
• Bread and bakery products
• Fortified milk and dairy products (cheese, yogurt)
• Instant soups and soup mixes
• Peanut butter and nut butters
• Fish fingers and processed seafood
• Margarine and spreads
• Sauces and condiments
• Processed meat products
• Energy drinks and fortified beverages
• Vitamin waters
• Fruit juices (fortified)
• Fortified flour and grain products
• Infant formulas and young children formulas
• Nutritional supplements
• Sports and energy drinks
• Dried baby food products
E101 is particularly prevalent in fortified breakfast cereals, bread, and powdered products where nutritional enhancement is marketing focus. The yellow coloring from riboflavin is often visible in these products.
Why Do Food Companies Use It?
E101 performs multiple critical commercial functions with unique advantages:
Dual function coloring + nutritional fortification: E101 riboflavin provides yellow coloring to foods while simultaneously adding essential vitamin B2 nutrition. At 0.5-5 mg/kg concentrations depending on food type, riboflavin imparts appealing yellow hue to cereals, bread, dairy products, and beverages while enriching them with vitamin B2. This dual function is unique among food colorants—most colorants (synthetic or natural) serve only aesthetic function, while riboflavin serves both aesthetic AND nutritional purposes.
Nutritional marketing advantage: Food manufacturers marketing “fortified with B vitamins” or “B-complex enriched” rely on E101 (and other B vitamins) as additives to meet nutritional claims and marketing positioning. The regulatory allowance for riboflavin use in many food categories reflects its essential nutrient status and dual function value.
Why riboflavin over synthetic colorants: E101 is selected for products emphasizing natural ingredients, nutrition, or “clean labels” because it is a naturally occurring essential vitamin, not a synthetic dye. The dual function (color + nutrition) makes it superior to pure colorants like tartrazine (E110) which provide only coloring without nutritional benefit. For health-conscious consumers and products targeting nutrition, riboflavin is the preferred choice.
Is It Safe?
E101’s safety status is EXCEPTIONAL—no Acceptable Daily Intake (ADI) is established because the compound is an essential nutrient with no documented toxicity at any exposure level from food use, supplementation, or therapeutic application.
Regulatory Status—Exceptional Safety Credentials:
• EFSA (Europe): Approved; no ADI established (considered safe at any level as essential nutrient); re-evaluated 2013 and confirmed safety
• FDA (USA): Approved as food additive and as essential nutrient supplement
• JECFA (WHO/FAO): Approved; no ADI established
• RDA (Recommended Dietary Allowance): 1.1-1.6 mg/day for adults; no toxicity at supplementation up to 400+ mg/day documented
✅ EXCEPTIONAL SAFETY PROFILE—ESSENTIAL NUTRIENT WITH NO KNOWN TOXICITY: E101 riboflavin has the most favorable safety status of virtually any food additive, reflecting its status as essential nutrient:
• No ADI established: EFSA, FDA, and JECFA do not establish ADI for riboflavin because it is an essential nutrient with no documented toxicity at any exposure level; this is the highest possible safety classification (reserved for essential nutrients and naturally safe substances)
• No toxicity documented: Decades of use as supplement (up to 400+ mg/day in some therapeutic applications) and in food fortification has yielded NO reports of adverse effects from riboflavin itself
• Water-soluble, non-accumulating: Excess riboflavin is not stored in the body; excess is excreted through urine, making accumulation toxicity impossible; users cannot “overdose” on dietary riboflavin because excess is automatically eliminated
• No genotoxicity: EFSA confirmed no genotoxic potential
• No carcinogenicity: No evidence of carcinogenic effects at any dose
• Essential nutrient status: Riboflavin is an essential nutrient—meaning humans cannot synthesize it and must obtain it from diet or supplementation; deficiency causes ariboflavinosis (recognized disease from vitamin B2 deficiency)
• Therapeutic use: Used as therapeutic agent for migraine prevention, eye health, skin conditions; medical applications at high doses support safety
• Photosensitivity characteristic: Riboflavin is a known photosensitizer; this is a property (not toxicity) that can elicit photoallergic reactions in hypersensitive individuals when combined with light exposure; occupational concern for workers handling pure powder, not typical consumer concern through food
• Safety for infants/children: Note: Some authorities recommend not using E101 in foods for infants and young children, not due to toxicity but as precautionary measure due to limited safety data in this population; however, riboflavin occurs naturally in breast milk and infant formulas
Documented safety findings:
• No toxicity at food levels: No adverse effects documented from E101 at food-use concentrations
• No toxicity at supplement levels: Supplementation at 10-400+ mg/day in humans shows no toxicity; water-soluble excess is excreted
• No accumulation: Riboflavin is not stored in tissues; excess is excreted; accumulation toxicity impossible
• Essential nutrient: Required for human health; deficiency causes disease; only concern is insufficient intake, not excessive intake
• Photosensitizer property: Known to elicit photoallergic skin/eye reactions in sensitive individuals when exposed to light; occupational hazard for workers handling dry powder, not consumer food exposure
• Dietary restrictions: No dietary restrictions for any religious or ethical groups; considered universally acceptable
• Allergy/Sensitivity: Extremely rare; true IgE-mediated food allergy not documented; photosensitivity is property, not allergy
• Metabolism: Rapidly absorbed and converted to coenzyme forms (FMN, FAD); metabolized and excreted as unchanged riboflavin and metabolites
• EFSA 2013 re-evaluation conclusion: “Riboflavin (E 101(i)) and riboflavin-5′-phosphate sodium (E 101(ii)) are unlikely to be of safety concern at the currently authorised uses and use levels as food additives”
Two Forms of E101
E101 exists in two regulatory designations representing different chemical forms:
• E101(i) – Riboflavin: The base vitamin form (C₁₇H₂₀N₄O₆); poorly soluble in water; yellow crystals; primary form for food coloring and supplementation
• E101(ii) – Riboflavin-5′-Phosphate Sodium: Phosphorylated form (sodium salt C₁₇H₂₀N₄NaO₉P); more water-soluble than base form; resembles the active coenzyme form in the body; used in beverages and products requiring better water solubility; equivalent safety profile to E101(i)
Both forms are chemically identical in their riboflavin core component; the phosphorylation in E101(ii) simply improves solubility without changing the fundamental compound’s safety profile.
Production Methods
E101 riboflavin is produced through three methods, all yielding identical final product:
Fermentation from yeasts (most common commercial method):
1. Yeasts (particularly Ashbya gossypii or Bacillus subtilis) are cultured in fermentation media
2. These organisms naturally produce riboflavin as secondary metabolite
3. Fermentation conditions are optimized to maximize riboflavin production
4. Riboflavin is extracted and purified from fermentation broth
5. Product is crystallized, dried, and standardized for purity
Genetically modified bacteria (increasingly used):
1. Bacillus subtilis or other bacteria are genetically modified to enhance riboflavin production
2. Fermentation proceeds similarly to wild-type organisms but with higher yields
3. EFSA has approved genetically modified strains (DSM 23096, KCCM 10445, CGMCC 13326) for food production
4. Produced riboflavin is chemically identical to naturally produced form
5. Final product is purified and standardized
Chemical synthesis (less common for food production):
1. 3,4-dimethylaniline and other chemical precursors are chemically coupled
2. Ribose sugar is incorporated
3. Product is purified through crystallization and standard chemical methods
4. Final product is chemically identical to fermentation-derived riboflavin
All production methods yield chemically identical E101 riboflavin. The fermentation method is most common due to cost-effectiveness and natural origin positioning.
Natural vs Synthetic Version
E101 riboflavin is naturally occurring and can be produced either from natural sources (fermentation) or through chemical synthesis, with both yielding identical final product:
Riboflavin occurs naturally in many foods (dairy, eggs, liver, vegetables). Commercial production typically uses fermentation from yeasts or genetically modified bacteria (representing natural origin), though chemical synthesis is also used. All forms—whether extracted from foods, fermented from microorganisms, or chemically synthesized—are chemically identical riboflavin (C₁₇H₂₀N₄O₆). The origin (natural vs synthetic) is irrelevant to the final product’s safety or function.
Health Functions and Essential Nutrient Role
E101 riboflavin functions as essential coenzyme precursor with documented health roles far beyond its additive function:
Riboflavin is converted in the body to two major coenzymes: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These coenzymes participate in hundreds of enzymatic reactions including: energy production from carbohydrates, fats, and proteins; antioxidant defense (glutathione reductase); amino acid metabolism; DNA repair; myelin (nerve sheath) formation; red blood cell production; hormone synthesis; and detoxification of foreign compounds and reactive oxygen species.
Riboflavin deficiency causes ariboflavinosis—a recognized disease characterized by angular cheilitis (cracks at mouth corners), glossitis (inflamed tongue), dermatitis, and peripheral neuropathy. The disease is now rare in developed countries due to food fortification and diverse diet, but remains concern in developing regions with limited food diversity.
Environmental and Sustainability
E101 production through fermentation from renewable carbohydrate sources (glucose) is highly sustainable, requiring no petroleum inputs or complex chemical synthesis. Genetically modified organisms for riboflavin production are approved based on environmental safety assessment by regulatory authorities (EFSA, FDA). The sustainability profile is excellent compared to synthetic colorants requiring energy-intensive chemical synthesis.
Comparison with Other Yellow Colorants
E101 riboflavin is unique among yellow food colorants due to its dual function and nutritional value:
• E101 (Riboflavin): Natural vitamin; dual function (color + nutrition); yellow hue; poor water solubility; essential nutrient; exceptional safety
• E110 (Tartrazine): Synthetic azo dye; yellow; water-soluble; excellent for beverages; potential allergenicity concerns; no nutritional value
• E102 (Allura Red): Synthetic; red color; different function
• E104 (Quinoline Yellow): Synthetic; yellow; water-soluble; no nutritional value
• Natural alternatives (beta-carotene, curcumin, annatto): Natural colors; variable solubility; no vitamin B2 benefit; different color profile
E101’s unique value is the dual function: it simultaneously colors and fortifies with essential vitamin. No synthetic colorant provides this dual benefit.
Consumer Actions Regarding E101
For consumers regarding E101:
• E101 is an essential nutrient with exceptional safety profile; presence in foods is beneficial for nutrition
• Yellow color in fortified cereals and bread often comes from riboflavin—indicating nutritional enhancement
• Naturally occurring in many foods; synthetic addition simply supplements natural sources
• Recommended dietary intake (RDA) is 1.1-1.6 mg/day for adults; food fortification helps meet this requirement
• Those seeking to increase B2 intake (common for migraine prevention, eye health) can rely on E101-fortified foods
• Photosensitizer property not relevant to consumers eating foods; concern is occupational for powder handlers
• Deficiency disease (ariboflavinosis) is rare in developed countries due to fortification; E101 contributes to preventing deficiency
• Universally acceptable for all religious, ethical, and dietary preferences (vegan, vegetarian, etc.)
The Bottom Line
E101 (riboflavin/vitamin B2) is an essential naturally occurring water-soluble B-complex vitamin with molecular formula C₁₇H₂₀N₄O₆, produced commercially through fermentation from yeasts or genetically modified bacteria or through chemical synthesis, approved by EFSA, FDA, and JECFA with exceptional safety status (no ADI established, reflecting essential nutrient status and zero documented toxicity at any exposure level), functioning as dual-purpose food additive providing both yellow food coloring and nutritional vitamin B2 fortification, with coenzyme precursor roles in cellular energy production, antioxidant defense, and metabolic processes essential for human health, and with safety profile superior to virtually all other food additives due to established requirement for human nutrition and inability to accumulate in body (water-soluble, excess excreted).
E101 is vitamin B2—an essential nutrient that cannot be synthesized by humans and must be obtained from dietary sources or supplementation. The compound functions as coenzyme precursor for flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), participating in hundreds of enzymatic reactions essential for energy metabolism, antioxidant defense, and cellular function.
The critical distinction of E101 is that it is the ONLY food additive that is simultaneously an essential human nutrient. Unlike other additives that serve primarily functional purposes (preservation, coloring, emulsification), E101 serves dual purpose: nutritional fortification AND food coloring. This makes it uniquely valuable—it enhances food both nutritionally and aesthetically.
The safety profile is exceptional: no ADI is established (the highest possible safety classification, reserved for essential nutrients and substances with zero toxicity concerns). No documented adverse effects exist at any exposure level from food use, supplementation, or therapeutic application. The water-soluble nature prevents accumulation—excess is automatically excreted through urine, making toxicity from overconsumption of dietary riboflavin impossible.
Riboflavin deficiency causes ariboflavinosis—a recognized disease characterized by mouth cracks, inflamed tongue, and skin problems. This disease is now rare in developed countries due to food fortification and diverse diets, but remains concern in developing regions. E101 fortification helps prevent this preventable deficiency disease.
For consumers, E101 represents a beneficial additive—improving nutritional profile while providing appealing yellow coloring. The exceptional safety profile, essential nutrient status, and dual functionality make E101 one of the most valuable and safest additives in the food supply.