The demand for natural, safe alternatives to synthetic food additives has never been higher. A groundbreaking 2025 study evidence for rosemary (Rosmarinus officinalis L.) as a dual-purpose solution: it stabilizes cooking oils and offers significant health benefits.
The Problem with Synthetic Antioxidants
Synthetic antioxidants like butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and tertiary butylhydroquinone (TBHQ) are chemicals added to oils to delay spoilage.
However, studies link these additives to severe health risks. For example, BHA breaks down into toxic byproducts like TBHQ and 2-tert-butyl-p-diquinone (TQJ), which cause DNA damage and tumor growth.
Similarly, BHT generates genotoxic compounds that disrupt energy metabolism, while TBHQ triggers oxidative stress and liver toxicity through the activation of the CYP1A1 enzyme, a protein involved in metabolizing toxins.
These risks, combined with stricter EU regulations (European Commission, 2011), have driven the search for natural alternatives.
Rosemary’s Bioactive Powerhouse
Rosemary contains over 20 bioactive compounds, with the most potent being carnosic acid, carnosol, rosmarinic acid, and 1,8-cineole. Carnosic acid, which makes up 40–50% of rosemary extract, neutralizes free radicals by donating hydrogen atoms.
Carnosol, another key compound, inhibits lipid peroxidation (the oxidative degradation of fats) three times more effectively than BHT.
Rosmarinic acid, a polyphenol, reduces inflammation by blocking COX-2 enzymes, proteins that promote inflammation.
Additionally, 1,8-cineole, a terpene found in rosemary essential oil, has antimicrobial and anti-inflammatory properties.
The method of extracting these compounds also matters. For instance, solvent-based extraction using ethanol yields 80.57 mg gallic acid per gram of total phenolic content (TPC), a measure of antioxidant-rich compounds.
Ultrasound-assisted extraction, which uses sound waves to break down plant cells, reduces processing time from 12 hours to 10 minutes while retaining 95% antioxidant activity.
Another advanced technique, encapsulation, involves enclosing rosemary extracts in protective coatings like liposomes.
Liposome-encapsulated rosemary extract retains 88% of its rosmarinic acid after six months of storage, making it ideal for long-term use.
Rosemary’s Role in Oil Stability
Frying at high temperatures (150–200°C) accelerates oil degradation through three main reactions: hydrolysis, polymerization, and oxidation.
Hydrolysis breaks down fats by water, producing free fatty acids. Polymerization forms large, sticky molecules that thicken oil, while oxidation creates harmful free radicals. Rosemary counters these processes effectively.
For example, the peroxide value (PV), which measures primary oxidation products like hydroperoxides, was significantly lower in rosemary-enriched oils.
In soybean oil, adding 1,000 ppm of rosemary extract reduced the PV from 28 meqO₂/kg in untreated oil to 16 meqO₂/kg after 10 hours of frying.
Similarly, rosemary lowered the formation of free fatty acids (FFA), which indicate hydrolysis and rancidity, by 26% in rapeseed oil. Conjugated dienes (CD), compounds formed during oxidation, also increased 50% slower in sunflower oil treated with rosemary extract.
Rosemary also reduces harmful byproducts formed during frying. For instance, it lowered 3-MCPD and glycidyl esters, toxic compounds linked to cancer, by 27% in palm oil.
Acrylamide, a carcinogen formed in starchy foods during frying, was reduced by 38% in potato chips fried in rosemary-enriched oil. Additionally, rosemary decreased polycyclic aromatic hydrocarbons (PAHs), cancer-causing chemicals, by 23.5% in soybean oil.
Impact on Oil Quality
Rosemary’s benefits extend to the physical, nutritional, and sensory qualities of oils. For example, viscosity, which measures the thickness of oil, increased by only 15.7 mPa·s in rosemary-treated hazelnut oil after six frying cycles, compared to 21.6 mPa·s in untreated oil.
Rosemary also slows the darkening of oils by stabilizing carotenoids, natural pigments responsible for color.
Control oils had twice the red and yellow values (measured via the Lovibond scale, a color grading system) compared to rosemary-enriched oils. Nutritionally, rosemary helps retain essential compounds like tocopherols (vitamin E) and omega-3 fatty acids.
Cottonseed oil with rosemary extract retained 96.61 mg/100 mL of tocopherols after 24 days, while untreated oil dropped to 62.27 mg/100 mL. Similarly, rosemary preserved 85% of α-linolenic acid, an essential omega-3 fatty acid, in flaxseed oil during storage.
Sensory quality is another area where rosemary shines. It reduces off-flavors like hexanal, a compound responsible for rancid odors, by 38% and heptanal by 17% in fried foods.
In blind tests, panelists rated rosemary-enriched oils 20% higher for freshness and aroma compared to untreated oils.
Health Benefits of Rosemary-Enriched Oils
Beyond stabilizing oils, rosemary offers numerous health benefits. For instance, its anti-inflammatory properties are well-documented.
Rats fed rosemary extract showed 40% less joint swelling due to reduced levels of TNF-α and IL-6 cytokines, proteins that drive inflammation.
Rosemary also reduced gastric acid secretion by 30% in animal models, making it a potential remedy for ulcers.
Rosemary’s antimicrobial activity is equally impressive. Rosemary essential oil (REO) at a 0.05% concentration inhibited the growth of foodborne pathogens like E. coli and Salmonella by 90%.
It also prevented mold growth in stored oils for up to six months, extending shelf life naturally. Metabolic and cognitive benefits further highlight rosemary’s versatility.
In hyperglycemic rats, rosemary extract improved insulin sensitivity by 25%, offering hope for diabetes management. Carnosic acid, a key compound in rosemary, reduced amyloid-beta plaques, protein clumps linked to Alzheimer’s disease, by 50% in lab studies.
Methods of Incorporating Rosemary into Oils
There are several ways to add rosemary to oils, each with its own advantages. Direct addition involves mixing rosemary extract directly into the oil.
For example, adding 0.08% rosemary extract to sunflower-palm oil blends extended frying life by 38%. Infusion techniques, such as traditional maceration, involve soaking dried rosemary in oil for 48 hours, which doubles the total phenolic content (TPC).
Microwave-assisted infusion reduces processing time to just 10 minutes while preserving 95% of volatile compounds.
Encapsulation is another effective method. Liposome-encapsulated rosemary extract retains 88% of its antioxidant activity after six months, compared to 50% in free extracts.
This technique is particularly useful in products like mayonnaise, where it reduces oxidation by 4.6 times.
Case Studies: Real-World Performance
Real-world applications demonstrate rosemary’s effectiveness. For instance, soybean oil treated with 1,000 ppm of rosemary extract allowed 40 frying cycles without replacement, compared to 20 cycles for untreated oil.
The induction period, which measures how long oil resists oxidation, increased from 2.22 hours in control oils to 3.4 hours with rosemary extract.
In palm oil, rosemary lowered 3-MCPD esters, toxic compounds formed during frying, by 27%. This not only improved safety but also reduced costs by $1.50 per liter in industrial settings.
Similarly, rosemary preserved 85% of α-linolenic acid in flaxseed oil during storage, compared to 60% in untreated oil.
Challenges and Solutions
Despite its benefits, rosemary faces challenges. High concentrations (>1,500 ppm) can cause bitterness, but blending it with thyme or oregano extracts can balance the flavor. The green tint from chlorophyll can be addressed using activated charcoal filtration.
Cost is another hurdle. Rosemary extract costs 50–100 per kilogram, compared to 10–20 for synthetic antioxidants. However, bulk purchasing and optimized extraction methods, like ultrasound, can reduce costs by 30%.
Regulatory hurdles also exist. The European Food Safety Authority (EFSA) requires batch-specific safety data for rosemary extract, but its clean-label appeal satisfies 85% of consumer surveys.
Future Directions
Future research could explore synergistic blends of rosemary with vitamin E or ascorbic acid, which boost antioxidant effects by 50%.
Long-term human trials are needed to confirm rosemary’s anti-diabetic and neuroprotective benefits. Additionally, using rosemary agro-waste (stems and spent leaves) could reduce extraction costs by 40%, making it more accessible.
Conclusion: A Greener, Healthier Future
Rosemary is a scientifically validated, multi-functional solution for the food industry. Replacing synthetic additives, it enhances oil stability, reduces toxic byproducts, and offers health benefits.
For example, it extends soybean oil shelf life by 53% and reduces acrylamide in fried foods by 38%. Rosemary-enriched oils may also lower inflammation and diabetes risk.
With the potential to save the food industry $2 billion annually, rosemary is poised to revolutionize food preservation and wellness as a powerful natural antioxidant.
Reference: Singh, P. K., Singh, N., Chopra, R., Garg, M., Chand, M., Dhiman, A., Homroy, S., & Talwar, B. (2025). Rosemary bioactives as antioxidant agents: A bidirectional approach to improving human health and vegetable oil stability. Food Chemistry Advances, 7, 100952. https://doi.org/10.1016/j.focha.2025.100952
