Rosemary extract beats synthetics for edible oil preservation

21-Jan-2010 - Last updated on 21-Jan-2010 at 11:45 GMT

A carnosic acid-rich extract from rosemary may extend the shelf-life of sunflower oil, and perform better than synthetic preservatives, says a new study.

Antioxidant-rich rosemary extracts were capable of inhibiting oxidation of sunflower oil, according to findings from a Chinese study published in Food Chemistry.

“Though sunflower oil is difficult to stabilise because of high linoleic acid content, [25, 60 and 98 per cent carnosic acid preparations] were proved to show strong protective effects against lipid oxidation of sunflower oil during accelerated storage,” wrote the authors, led by Ying Zhang.

“Results observed in our experiments showed that [25, 60 and 98 per cent carnosic acid preparations] could be considered as satisfactory for large scale applications,” they added.

Furthermore, the extract performed better than the more established synthetic preservatives such as like butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT), said the researchers from the Northeast Forestry University in Harbin.

According to a 2003 report by Frost and Sullivan, the synthetic antioxidant market is in decline, while natural antioxidants, such as herb extracts, tocopherols (vitamin E) and ascorbates (vitamin C) are growing, pushed by consumer desire acceptance and easier market access.

Study details

The researchers tested three rosemary extracts with different levels of carnosic acid, including 25, 60, and 98 per cent. The degree of spoilage was analysed in sunflower oil by measuring peroxide values, thiobarbituric acid-reactive substances (TBARS), and free fatty acid contents during accelerated storage. They antioxidant and preservative ability was also compared to vitamin C (ascorbic acid), and the synthetics, BHA, BHT, and tert-butyl hydroquinone (TBHQ).

In terms of the peroxide levels, only TBHQ performed better than the 98 per cent carnosic acid extract for inhibiting peroxide and hydroperoxide formation. Furthermore,

Using the TBARS assay to measure the degree of lipid oxidation, the Chinese researchers report that that the 98 per cent carnosic acid extract reduced TBARS formation by over 60 per cent, compared to under 50 per cent for BHA and BHT. Again, only TBHQ performed better, inhibiting TBARS by about 75 per cent.

The 98 per cent extract “was to a greater extent more effective than commonly-employed synthetic antioxidants BHT and BHA, but less effective than the synthetic antioxidant TBHQ”, said the researchers.

Source: Food Chemistry
Volume 118, Issue 3, Pages 656-662
“Oxidative stability of sunflower oil supplemented with carnosic acid compared with synthetic antioxidants during accelerated storage”
Authors: Y. Zhang, L. Yang, Y. Zu, X. Chen, F. Wang, F. Liu