Carnosic acid

Carnosic acid is the primary oil-soluble phenolic compound of rosemary leaf. Together with carnosol, it accounts for over 90% of the antioxidant activity of rosemary extract [3], [4]. Food producers buy rosemary extract to delay lipid oxidation in oils, meats, and frying fats [5], [6]. In the market, it is often referenced by the additive number E392. Rosmarinic acid is the water-soluble compound of the same plant. It is a separate product and acts differently.

Where is it in rosemary, and how much is there?

In the leaf, not in the essential oil. Rosemary essential oil is obtained by steam distillation and contains completely different compounds. In 12 samples from Spain, the main components were camphor (17.2 to 34.7%), alpha-pinene (10.2 to 21.6%), and 1,8-cineole (12.1 to 14.4%) [7]. Carnosic acid is non-volatile and does not transfer into the distillate.

The ratio varies by season and location. In rosemary samples collected monthly from Adana, Mersin, and Antalya, both location and harvest time significantly changed carnosic acid and carnosol levels. The richest carnosic acid sample came from Antalya in September, with 0.74% in plant material. The highest carnosol occurred at the same location in February, at 0.78% [8]. Therefore, the name "rosemary extract" alone does not promise a specific concentration.

The concentration is much higher in extracts, but depends on the method. In an extract obtained with supercritical CO₂, carnosic acid was 35.2 g/kg (3.5%) and carnosol was 0.46 g/kg [9]. In a commercial extract used in a food-contact film study, carnosic acid was 7.0% and carnosol was 0.9% [10]. A study on ethanol-water mixtures reported pure ethanol as best for carnosic acid, and 30% ethanol for rosmarinic acid [11]. Same leaf, different solvent, different product.

Carnosic acid, carnosol, rosmarinic acid: what is the difference?

Values are taken from PubChem. XLogP indicates whether a substance is lipophilic or hydrophilic. Higher values indicate higher lipophilicity. Carnosic acid is lipophilic at 4.9, while rosmarinic acid is hydrophilic at 2.4. This difference determines in which product matrix each compound works. Ursolic acid originates from the waxy leaf layer and can accompany the extract.

Carnosol is the converted form of carnosic acid. When carnosic acid loses two hydrogens and forms a cyclic lactone ring, it becomes carnosol. In formulas, this shows as a shift from 332.4 to 330.4 g/mol without changing oxygen count. When carnosic acid oxidizes, it also forms quinone derivatives [12]. In ethanol solution, degradation of all three substances increased with temperature, and light formed distinct degradation products [13]. In fish oil, carnosic acid degraded much slower. When all three were present, carnosic acid protected carnosol levels at the expense of its own degradation [13].

Carnosol is also an antioxidant, but acts differently. In corn oil, carnosic acid and rosmarinic acid were significantly more effective than carnosol. In oil-in-water emulsions, carnosic acid and carnosol outperformed rosmarinic acid [14]. A study comparing five rosemary extracts showed carnosic acid was stronger than carnosol. The same study reported that the presence of carnosol enhanced overall efficacy [2].

The ratio reflects the product history. Two types of rosemary extract added to lamb feed were compared: carnosic acid/carnosol ratio 1:1 (14 to 16%) and 2:1 (25 to 11%). The authors reported that carnosol stabilized the diterpene fraction during feed processing [15].

Rosmarinic acid acts in water. It comes from the same leaf but is a distinct product. In oil-in-water emulsions, it remained less effective than carnosic acid and carnosol. Authors attributed this to its partitioning into water rather than protecting the oil interface [14]. In distillation wastewaters of basil, rosemary, and sage, the main phenolic compound was rosmarinic acid, measured at 29 to 135 mg per 100 mL [16].

Essential oil markers carry the odor. 1,8-cineole and camphor are the main components of rosemary essential oil [7]. In an extract bought for antioxidant purposes, odor is usually undesirable. Therefore, the volatile matter row on the certificate should be checked.

What is it used for?

Oils and frying. In a study adding carnosic acid to rapeseed oil at 180 °C, oil degradation markers decreased [6]. In another study by the same group, 700 mg/kg carnosic acid gave the lowest degradation rate for polyunsaturated fatty acids during prolonged thermal treatment. As a benchmark, 200 mg/kg TBHQ was used [17].

Meat products. In pork sausage, 2,500 mg/kg rosemary extract showed equal efficacy to a BHA/BHT mixture. In frozen raw sausage, rosemary extract was more effective than BHA/BHT [5]. In liver pâté, rosemary extract reduced lipid oxidation without altering color stability. As extract dosage increased, carnosic acid concentration in the product rose [18]. In fresh pork sausage, rosemary extract alone gave an antioxidant effect comparable to chitosan [19]. In beef, 800 and 1,600 mg/kg rosemary extract delayed microbial spoilage and lipid oxidation, with best results from the encapsulated form [20].

Milk powder. In fat-filled milk powder, a mixture of carnosol, carnosic acid, and rosmarinic acid at 308 mg/kg suppressed all primary and secondary oxidation markers. In certain assays, it was less effective than a 200 mg/kg BHA/BHT mixture [21].

Common limitation of studies. Most food trials do not report the carnosic acid concentration of the extract used. Therefore, the dosage in a study belongs to that specific product and cannot be directly transferred to another extract.

Oil-soluble, water-soluble, or essential oil: which form?

Three distinct products come from rosemary, and they are not equivalent.

Oil-soluble extracts are often sold diluted in edible oil. The certificate must state whether the percentage refers to the pure extract or the diluted oil solution.

The choice depends on four questions.

• Is the product oily or aqueous? Carnosic acid works in the lipid phase. Behavior changes in emulsions (see "Behavior in formulation").
• Is odor acceptable? Residual essential oils carry a rosemary scent [7]. If odor is undesirable, check the volatile matter row on the specification.
• How much is needed? Dosages vary by product matrix. Sausage studies used 2,500 mg/kg extract [5], beef used 800 to 1,600 mg/kg [20], milk powder used 308 mg/kg active blend [21], and thermally treated rapeseed oil used 200 to 700 mg/kg carnosic acid [17]. Regulatory limits depend on product category and apply to the sum of carnosol and carnosic acid [23].
• Price. Compare the price per kilogram of carnosic acid, not per kilogram of extract. If aiming for 500 mg/kg carnosic acid in 1 ton of oil, a 3.5% extract requires 14.3 kg, while a 7.0% extract requires 7.1 kg [9], [10]. These figures are examples.

Why rosemary when synthetics exist? In a laboratory test comparing eight antioxidants, all five tested rosemary extracts outperformed synthetics [2]. In pork sausage, rosemary extract matched a BHA/BHT mixture and led in frozen raw sausage [5]. Three key differences remain.

First is regulatory scope. Permitted food categories for each antioxidant are defined by law. Rosemary extracts are authorized as food additives with limits set per category [23]. Synthetic antioxidants have narrower category permissions. Therefore, the first question is usually which antioxidant is permitted in the specific product category. Check the specific category rules and current regulations.

Second is thermal stability. Carnosic acid maintained protection at 180 °C [6]. In frying and prolonged heating, this remains a distinct technical advantage.

Third is synergy. Carnosol enhances efficacy [2], and combined use with alpha-tocopherol extended shelf life [24]. Synthetic antioxidants lack these natural synergies.

Clean labeling is another factor. Rosemary extract appears on the ingredient label under a plant name consumers recognize. The final decision depends on these four factors.

How to read the Certificate of Analysis?

Method. Carnosic acid and carnosol are quantified using high-performance liquid chromatography (HPLC) [25]. The certificate should state the analytical method.

Analytical sensitivity. Pure carnosol in solution degrades within hours, whereas pure carnosic acid persists for days depending on the solvent. Carnosol purity dropped from 95% to 70% within 30 hours in solution. In contrast, these compounds remained stable within whole rosemary extract [25]. A low test result can stem from sample preparation rather than product quality.

Carnosic acid and carnosol must be listed separately. The total is needed for regulatory compliance, but individual values reveal more about the product. Because carnosol is an oxidation product of carnosic acid, their ratio reflects thermal and oxygen exposure [13].

"E392" is not a single compound. It is a European food additive code for "extracts of rosemary." The code does not specify extract type, carnosic acid content, or extraction solvent. These details appear on the certificate.

Regulations measure the sum, not the ratio. Regulatory limits for E392 apply to the sum of carnosol and carnosic acid [23]. Analytical testing methods in food matrices target this sum [26]. The two rows on the certificate answer two distinct questions. The sum covers regulatory and labeling compliance. The ratio reflects processing history and antioxidant performance. Rosemary extracts were evaluated in Europe in 2008 [27]. In 2016, JECFA set a temporary ADI of 0 to 0.3 mg/kg body weight for carnosic acid plus carnosol [23]. Confirm specific status via manufacturer documentation.

Carrier oil ratio. Does the percentage refer to the final solution or the pure extract? The certificate should identify the carrier and its proportion.

Rosmarinic acid row. Rosmarinic acid should not appear in oil-soluble extracts. It is the main compound in water-soluble extracts [11]. If listed in an oil-soluble product, verify product identity.

Specification vs result. A specification is the manufacturer standard. The measured value is the specific lot result. The Technical Data Sheet (TDS) is a general document. The Certificate of Analysis (CoA) belongs to the specific lot.

What indicates quality?

Solvent residues. Residues depend on the extraction solvent. If ethanol, hexane, acetone, or CO₂ was used, check the solvent type and residue limits.

Pigments. Rosemary leaves contain chlorophyll and carotenoids. These pass into the extract and darken its color. Selective extraction can separate these pigments [22].

Raw material testing. Request test results for pesticides, mycotoxins, and heavy metals in the botanical raw material.

Behavior in formulation

Bulk oil vs emulsion. Carnosic acid is strong in lipid phases. In oil-in-water emulsions, all rosemary compounds performed lower than in bulk oil. Carnosic acid and carnosol weakened as emulsion pH approached neutrality [14]. In emulsions, evaluate dosage and pH together. For aqueous systems, carnosic acid requires a carrier or emulsifier.

Heat. Carnosic acid maintained protection at 180 °C [6]. It acts sacrificially: degradation in ethanol increased with temperature, and in mixtures, carnosic acid preserved carnosol levels while degrading itself [13]. For high-heat processes, calculate starting dosage considering this consumption rate.

Storage. Degradation accelerates with temperature, and light creates distinct breakdown products [13]. Store opened extract cool, sealed, and protected from light. Carnosol content will naturally increase over time.

Synergies. In sardine oil, rosemary extract (0.02%) combined with alpha-tocopherol (0.05%) extended protection by 5 days compared to individual use, matching BHA performance [24].

Pro-oxidant risks. In specific in vitro models, these compounds showed pro-oxidant behavior. Carnosol and carnosic acid increased DNA damage in one assay, while acting as radical scavengers in another [3]. These are experimental model findings, not food matrix outcomes.

Safety and labeling. Follow the Safety Data Sheet (SDS) during handling. Label naming and additive numbers depend on food category and local regulations.