Extracts from oregano and rosemary could extend the shelf-life of omega-3-rich fish oil, suggests new research from the US.
Fish oil is notoriously difficult to incorporate into formulations since it is highly susceptible to oxidation. The result is a fishy taste and smell which can be off-putting for consumers.
However the nutritional properties of fish oil have been much in the spotlight in recent years, especially omega-3, of which fish is recognized as the best source. In order to help people consume omega-3 in their diet - and especially those who have an aversion to fish - formulators have sought to overcome the stability issues and deliver food products that are untainted by sensory issues.
"This study provides useful information relative to natural antioxidants used in stabilizing fish oil during cooking and storage," wrote the authors in the Journal of Food Science.
"It could also be beneficial to the food industry in the development of functional foods enriched with healthy long chain unsaturated fatty acids with a longer shelf life," they added.
Researchers from Louisiana State University tested the efficacy of methanol extracts of oregano and rosemary at different concentrations to retard the oxidation of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in menhaden oil.
Extracts were added at a concentration of zero, one, 2.5 and five per cent, and the oil was subsequently subjected to an accelerated ageing study by heating at 150 degrees Celsius for 30 min or incubating at 60 degrees Celsius fro five days.
In the oil subjected to heating at 150 degrees Celsius in the absence of the herb extracts, only 15.9 per cent of DHA and 18.5 per cent of EPA remained in the fish oil. All of the EPA and DHA was found to have been oxidised in the extract-free oil incubated at 60 degrees Celsius for five days.
However, when one and five per cent oregano extract was added, the oil contained 39 and 66 per cent, respectively, of the original DHA content after heating at 150 degrees Celsius, and 45 and 69 per cent, respectively, of the original EPA content.
The highest retentions of DHA (57 per cent) and EPA (58 per cent) in fish oil with added rosemary were found for 2.5 per cent rosemary.
The same concentration of rosemary produced the best results after incubation at 60 degrees Celsius for five days, 88 per cent of the original DHA and EPA contents retained.
The Louisiana-based researchers note that, while the rosemary extract performed better at mild temperatures, the oregano extract performed better at higher temperatures.
"Thus, for food preservation purposes, rosemary extract may be more effective than oregano extract," stated the researchers.
"However, at higher cooking temperature, the antioxidants in oregano extract are more stable and stronger than those in rosemary extract in retarding fish oil oxidation," they added.
"The results in this study support the use of spicy plants as sources of natural antioxidants," concluded the researchers.
Another aspect that boosts the potential in the market place is the natural source of the seed flours. At present, 'natural' is a powerful force in the food industry, and there is increasing resistance at regulatory and consumer level - as well as from food retailers and manufacturers aiming to meet their demands - to synthetic preservatives.
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 easier consumer acceptance and legal requirements for market access.
Food manufacturers are getting increasingly adventurous with the food product categories they are adding omega-3 to. Last week Premier Foods' Branston brand in the UK announced the launch of baked beans with omega-3 - but the source of the omega-3 was not revealed.
Other categories in which omega-3 has turned up include bread, dairy products, baked goods, and chewy sweets.
Source: Journal of Food Science
Published on-line ahead of print 1st November 2007, doi: 10.1111/j.1750-3841.2007.00569.x
"Oregano and Rosemary Extracts Inhibit Oxidation of Long-Chain n-3 Fatty Acids in Menhaden Oil"
Authors: S.D. Bhale, Z. Xu, W. Prinyawiwatkul, J.M. King, and J.S. Godber