Hydroxytyrosol, a natural polyphenol from olives, may extend the shelf-life of fish products to the same extent as synthetic preservatives, suggests new research.
Fish is notoriously difficult to incorporate into formulations since the oil 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.
Hydroxytyrosol, thought to be the main antioxidant compound in olives, and may be a possible solution to this problem, after the oxidative stability of bulk fish oil, oil-in-water emulsions, and frozen minced fish muscle, suggests new findings published in the Journal of Agricultural and Food Chemistry.
"The results of the present work emphasize the efficiency and versatility of hydroxytyrosol to stabilize foodstuffs rich in functional omega-3 PUFAs," wrote lead author Manuel Pazos from Spain's Instituto de Investigaciones Marinas (CSIC).
"Hydroxytyrosol demonstrated an antioxidant capacity similar to that of synthetic propyl gallate in oil-in-water emulsions and frozen fish muscle."
The natural source of the polyphenol could also boost the potential in the market place. 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, such as like butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT).
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.
Pazos and co-workers tested the efficacy of different concentrations of the olive polyphenol (10, 50, and 100 ppm) to three different fish oil-rich foods: bulk cod liver oil (40 per cent omega-3), cod liver oil-in-water emulsions (four per cent omega-3), and frozen minced horse mackerel muscle.
The Spanish researchers report that hydroxytyrosol was able to inhibit lipid oxidation in all the food systems tested. The optimal concentrations depended on the food system, however, with 100 ppm performing best in bulk oil and oil-in-water emulsions, and 50 ppm producing optimal results in the frozen minced fish muscle.
Inhibition of the loss of vitamin E (R-tocopherol) and omega-3 fatty acids was also observed in minced muscle, added the researchers.
"A concentration of 50 ppm of hydroxytyrosol was best to maintain a longer initial level of R-tocopherol (approximately 300 micrograms per gram of fat), whereas both 50 and 100 ppm of hydroxytyrosol were able to preserve completely omega-3 PUFAs," wrote Pazos.
Moreover, when compared to the synthetic preservative propyl gallate, an equivalent antioxidant activity was observed for hydroxytyrosol in emulsions and frozen fish muscle.
Health benefits of olive compound
The polyphenol also brings some potential health benefits of its own. Previous research found that LDL or 'bad' cholesterol levels could be cut substantially after consuming just 25 millilitres of virgin olive oil daily for one week. Other studies have suggested that it could also boost bone health, protect against cancer, may also benefit eye health.
Source: Journal of Agricultural and Food Chemistry
Published online ahead of print, ASAP Article, 22-Apr-2008; doi: 10.1021/jf073403s
"Hydroxytyrosol Prevents Oxidative Deterioration in Foodstuffs Rich in Fish Lipids"
Authors: M. Pazos, A. Alonso, I. Sanchez, I. Medina