Thermal stability and antioxidant activity of essential oils from aromatic plants farmed in Argentina

• Essential oils reduce formation of oxidation volatile compounds in vegetable oils.
• Essential oils have high antioxidant activity.
• Heating process modify chemical composition of the essential oils.
• Oregano, Laurel, and Rosemary essential oils can be used as food antioxidant agents.
• Essential oils prepared in organic condition can be included in organic food.

Food industries are looking for natural antioxidant to replace synthetic because these last ones are questioned due to healthy reasons. Essential oils are natural products that can have antioxidant activity, but their composition and antioxidant activity could change for thermal storage condition. The objective of this study was to evaluate the antioxidant effect and thermal stability of rosemary, oregano and laurel essential oils (EO). The major components of the essential oils were terpineol (E) Beta (55.5%), terpinen-4-ol (15.9%), and thymol (12.9%) in oregano; camphor (35.7%), verbenone (26.6%), and β-caryophyllene (15.8%) in rosemary EO; and linalool (45.0%), sabinene (31.9%), and methyl eugenol (14.3%) in laurel EO. The volatile composition of the EO changed during the thermal stability study. The antioxidant activity of the essential oils was analyzed measuring free-radical scavenging activity (FRSA) and total phenolic content; and performing a storage study of sunflower oil measuring the formation of peroxide and volatile oxidation compounds. The FRSA showed that laurel (61.74%), oregano (59.97%), and rosemary (48.23%) EOs showed better percentage inhibitions than BHT (8.76%). In the storage study of sunflower oil, samples with 0.10% oregano EO, 0.02% oregano EO, 0.02% laurel EO, and 0.10% rosemary EO showed better antioxidant properties, exhibiting less peroxide and anisidine values during storage. Also, 0.02% oregano EO in the storage study showed reduced formation of volatile compounds like hexanal, 2-heptenal, and 2,4-decadienal. The studied EOs have antioxidant activity and constitute natural potential agents that could be used as antioxidants in food products. Also, the studied EOs are compounds that change under high temperature conditions during storage, which could affect their potential antioxidant activity.