Effect of Drying on Herbal Antioxidants

DUBLIN, IrelandHeightened demand in natural products is stimulating interest in antioxidant content of herbal ingredients. To determine how processing affects antioxidants levels, Irish researchers investigated the effect of common drying processes on Lamiaceae herbs (rosemary, oregano, marjoram, sage, basil and thyme).

On a fresh-weight basis, certain herbs have a higher antioxidant activity than fruits and vegetables. Three types of oreganoMexican (Poliomintha longiflora), Italian (Origanum x majoricum) and Greek mountain (Origanum vulgare ssp.hirtum)have the highest antioxidant activity of a number of culinary herbs.

The food industry has been using the antioxidant properties of some of these herbs to slow down or prevent food-product oxidation and extend shelf life. One of the most widely used, rosemary extracts derived from Rosmarinus officinalis, contains several compounds, including rosmarinic acid and phenolic diterpenes carsonol and carnosic acid. These extracts have free-radical scavenging activity that provides antioxidant power in many applications including snacks, baked goods, meat and other products.

To determine how the antioxidant content of oregano, rosemary and the other herbs might change with processing, the scientists investigated changes in their total phenols, rosmarinic acid content and antioxidant capacity after three drying treatments: air-, freeze- and vacuum oven-drying. The dried herbs were stored for 60 days at -20°C and compared to fresh samples. The air-dried herbs had significantly higher total phenols, rosmarinic acid content and antioxidant capacity than the freeze-dried and vacuum oven-dried samples throughout the storage period. Vacuum oven-drying had better results than freeze-drying, with higher total phenol content and ferric-reducing antioxidant property (FRAP) values in rosemary and thyme during the storage period. However, the ORAC assay only showed a significantly higher difference in thyme antioxidants. The fresh samples had the lowest antioxidant values by weight for all the factors tested.